I joined the Kohl Research Group in the middle of February, 2017 as a postdoctoral fellow after completing my Ph.D. at the Indian Institute of Technology, Patna. My doctoral work focused on the synthesis and characterization of organometallic catalysts for the ring opening polymerization of cyclic esters and polymerization of ethylene. In addition, I worked on the synthesis of polycarbonates and cyclic carbonate from epoxides and CO2 using transition metals. I was awarded Erasmus Mundus fellowship (a program funded by the European Union) in 2014 and visited Johannes Kepler University at Linz, Austria as a Ph.D. exchange student for 11 months during my Ph.D studies. I am working here on the synthesis and characterization of the state-of-the-art anion conducting polymers based on all carbon backbones for electrochemical devices (fuel cells, electrolyzers, and dialysis). Supervisors: Prof. Paul A. KOhl, Prof. Debashis Chakraborty, and Prof. Uwe Monkowius
Role of Water Molecules in Enabling Site Hopping and Vehicular Transport Mechanisms in Polynorbor... more Role of Water Molecules in Enabling Site Hopping and Vehicular Transport Mechanisms in Polynorbornene-based Anion Exchange Membrane Zhongyang Wang, ⸹ Ge Sun ， ⸹ Mrinmay Mandal, ‡, Paul A. Kohl, ‡, Juan de Pablo, ⸹ Shrayesh N. Patel, ⸹ and Paul F. Nealey ⸹ ‡ School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, 30332-0100, United States ⸹ Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA Ion exchange membranes are at the heart of electrochemical conversion and storage devices such as fuel cells 1, water electrolyzers 2, CO2 electrolyzers 3. redox flow batteries 4, and reverse electrodialysis 5. Anion exchange membrane fuel cells (AEMFCs) have attracted enormous attention as alternatives to replace perfluorinated, sulfonic acid-based proton exchange membrane fuel cells (PEMFCs) 6 because alkaline membrane electrode assemblies (MEAs) composed of anion exchange ionomers (AEIs) and AEMs that allow the use of Ni 7, 8, Fe 9, and Ag 10 based precious-group-metal (PGM) free catalysts in alkaline environments for hydrogen oxidation reactions (HORs) and oxygen reduction reactions (ORRs). However, the lack of understanding of ion transport mechanisms at different hydration levels of an anion exchange membrane hinders the rational design of the MEAs in an AEMFC. Here we investigate site hopping and vehicular transport mechanisms using anion exchange thin films, interdigitated electrodes, and atomistic molecular dynamics simulations. Halide ion (Br-, Cl- and I-) conductivities in polynorbornene-based thin films are measured as a function of temperature and relative humidity using electrochemical impedance spectroscopy. Halide ions show Arrhenius behaviors, and activation energy (Ea) is for the first time used as an indicator for detecting the transition of site hopping and vehicular transport mechanisms. Using atomistic molecular dynamics simulation, we quantitatively demonstrate that the transition of site hopping and vehicular mechanisms is aided by better solvation environments of anions and more percolated water pathways. References Z. Wang, J. Parrondo, C. He, S. Sankarasubramanian and V. Ramani, Nature Energy, 2019, 4, 281-289. S. Z. Oener, M. J. Foster and S. W. Boettcher, Science, 2020, 369, 1099-1103. D. A. Salvatore, C. M. Gabardo, A. Reyes, C. P. O’Brien, S. Holdcroft, P. Pintauro, B. Bahar, M. Hickner, C. Bae, D. Sinton, E. H. Sargent and C. P. Berlinguette, Nature Energy, 2021, 6, 339-348. K. Lin, Q. Chen, M. R. Gerhardt, L. Tong, S. B. Kim, L. Eisenach, A. W. Valle, D. Hardee, R. G. Gordon, M. J. Aziz and M. P. Marshak, Science, 2015, 349, 1529-1532. R. D. Cusick, Y. Kim and B. E. Logan, Science, 2012, 335, 1474-1477. J. Wang, Y. Zhao, B. P. Setzler, S. Rojas-Carbonell, C. Ben Yehuda, A. Amel, M. Page, L. Wang, K. Hu, L. Shi, S. Gottesfeld, B. Xu and Y. Yan, Nature Energy, 2019, 4, 392-398. G. Braesch, Z. Wang, S. Sankarasubramanian, A. G. Oshchepkov, A. Bonnefont, E. R. Savinova, V. Ramani and M. Chatenet, Journal of Materials Chemistry A, 2020, 8, 20543-20552. S. Kabir, K. Lemire, K. Artyushkova, A. Roy, M. Odgaard, D. Schlueter, A. Oshchepkov, A. Bonnefont, E. Savinova, D. C. Sabarirajan, P. Mandal, E. J. Crumlin, Iryna V. Zenyuk, P. Atanassov and A. Serov, Journal of Materials Chemistry A, 2017, 5, 24433-24443. H. Adabi, A. Shakouri, N. Ul Hassan, J. R. Varcoe, B. Zulevi, A. Serov, J. R. Regalbuto and W. E. Mustain, Nature Energy, 2021, 6, 834-843. H. Erikson, A. Sarapuu and K. Tammeveski, ChemElectroChem, 2019, 6, 73-86.
Anion exchange membrane fuel cells (AEMFCs) have recently shown excellent progress in terms of th... more Anion exchange membrane fuel cells (AEMFCs) have recently shown excellent progress in terms of their performance − e.g., achievable power and current density. However, very few AEMFCs have been demonstrated with the ability to operate for a long duration (>1000 h). In addition, it is unknown whether performance losses observed during operation are reversible, irreversible, or a combination of the two. In this study, a high-performance AEMFC operated continuously at 600 mA/cm 2 for 3600 h (150 days) at 80°C with H 2 /O 2 reacting gases was demonstrated. Throughout testing, the electrochemical properties of the AEMFC were probed to provide information about performance degradation pathways and their degree of reversibility. It was found that a portion of the performance loss that occurs during AEMFC operation was due to suboptimal reaction conditions and can be recovered. At the end of the experiment, the cell was disassembled, and its structure and composition were evaluated at the nanoscale by aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. The structure and composition of the electrode were compared to cells at the beginning of their operational life. It was found that the primary mechanism for long-term AEMFC performance loss was catalyst agglomeration. During the operational time, there was no evidence of significant polymer degradation, likely due to the high hydration state of the cell. By documenting the long-term changes in high-performing AEMFCs, this work provides important information for the systematic design of cell components and demonstrates the importance of controlling cell operation, which can aid in the commercialization and widespread deployment of low-cost, long-life AEMFCs.
Low-temperature water electrolysis using an anion conductive polymer electrolyte has several pote... more Low-temperature water electrolysis using an anion conductive polymer electrolyte has several potential advantages over other technologies, however, the fabrication of durable alkaline electrodes remains a challenge. Detachment of catalysts results in the loss of electrochemical surface area. Simple mixtures of ionomer and catalyst can suffer from poor catalyst adhesion because only physical adhesion is used to bind the components together. A family of chemically bonded, self-adherent, hydroxide conducting ionomers were synthesized and tested under alkaline electrolysis conditions with nickel ferrite anode electrocatalysts and platinum-nickel cathode catalyst. The ionomers are based on hydroxide conducting poly(norbornene) polymers used as the solid polymer electrolyte in alkaline fuel cells and electrolyzers. The synthesized terpolymer ionomers have been functionalized to provide pendant sites for covalent chemical bonding of bis(phenyl)-A-diglycidyl ether to the ionomer, catalyst, and porous transport layer. The electrodes show excellent adhesion between the catalyst particles, porous transport layer and ionomer, as determined by adhesion measurements and electrolysis performance. The AEM electrolyzer had stable voltage performance under high current density (1 A/ cm 2 at 1.83 V (67% voltage efficiency)) for extended time periods (>600 h) without degradation.
The behavior of the oxygen-evolving positive electrode (i.e. anode) in the anion exchange membran... more The behavior of the oxygen-evolving positive electrode (i.e. anode) in the anion exchange membrane water electrolyzer (AEMEL) is complex and influenced by several factors. Very few studies have been performed to understand oxygen evolution reaction (OER) behavior by optimizing the individual factors that influence performance. This study highlights the effects of catalyst loading, catalyst selection, porous transport layer (PTL) type and conductive additive content. The influence of each factor is elucidated through a design of experiments (DoE) approach with a full statistical analysis. Electrochemical data, alongside Pareto charts, parametric trends and their mutual interactions are discussed. This DoE approach is also helpful in making useful predictions and discovering new combinations to be tested. The end result was a high-performance AEMEL able to operate at a current density of 1.0 A/cm 2 at 1.80 V with IrOx OER and PtNi hydrogen evolution reaction (HER) catalysts using 0.3 M KOH fed to the anode. Even lower operating voltage was observed with PbRuOx catalyst at the anode, 1.64 V @ 1.0 A/cm 2 , though the cell decay rate was higher. Lastly, a IrOx/PtNi cell was stably operated continuously for 30 days (720 h) at 1.0 A/cm 2. This study can serve as a guide for optimal electrode design with insights into component-performance compromises, which can aid in making design choices and performing techno-economic analyses.
The cheaper and easy to handle catalysts are particularly important for catalytic studies. Herein... more The cheaper and easy to handle catalysts are particularly important for catalytic studies. Herein, inexpensive Co 2 O 3 and MnO 2 were used as catalysts for the ring-opening polymerization (ROP) of rac -lactide ( rac -LA) and ε- caprolactone ( ε -CL). The polymerization proceeded in a controlled manner with the formation of high molecular weight ( M n ) and narrow dispersity (Ð). Heterotactically enriched ( P r up to 0.7) poly(lactic acid) (PLA) was formed during the polymerization process. MALDI-TOF and 1 H NMR analyses of low M n oligomer from rac -LA indicated that the polymerization followed an activated monomer mechanism. The data on the polymerization kinetics showed that the polymerization followed first order kinetics.
CO 2 reduction reaction (CO 2 RR) is a promising way to convert CO 2 into value-added products. M... more CO 2 reduction reaction (CO 2 RR) is a promising way to convert CO 2 into value-added products. Membrane-based gas-phase CO 2 RR offers several advantages like high selectivity and energy efficiency. However, high product crossover and poor CO 2 utilization in anion exchange membranes (AEMs) prevents the utilization of AEMs for CO 2 RR. The acidic environment of the cation exchange membrane can negatively influence the CO 2 reduction reaction (CO 2 RR) activity by favoring the competing hydrogen evolution reaction (HER). Hence, it is necessary to manipulate the local pH environment of the electrodes to yield maximum productivity. Bipolar membranes (BPMs) with a cation exchange layer (CEL) and an anion exchange layer (AEL) help in maintaining different local pH environments at each electrode. Now, a bipolar membrane fabrication with a weak-acid cation exchange layer removes the possibility of competing HER without affecting CO 2 RR. The increasing demand for energy due to population growth and rapid industrialization results in extensive CO 2 emissions in the atmosphere. Renewable energy sources (such as solar cells and wind power) powered production of value-added chem-icals/fuels and storage of emission-free renewable energy by the electrocatalytic CO 2 reduction reaction (CO 2 RR) is a promising approach to mitigate the increased risk associated with the increase in CO 2 concentration in the atmosphere. [1,2] Aqueous-phase CO 2 RR offers low current density because of the low solubility and slow diffusion of CO 2 in aqueous media. [3] Gas-phase membrane-based CO 2 RR by constructing electrochemical cells consisting of a membrane electrode assembly (MEA) has shown higher product selectivity and energy efficiency. [3-6] In anion exchange membrane (AEM), the problems with high product crossover, poor CO 2 utilization, and low ionic conductivity in comparison to CEM prevent the widespread adoption of AEMs for CO 2 RR. [7] However, the problems with low ionic conductivity and poor alkaline stability are systematically addressed with the development of recent AEMs. [8-10] In cation exchange membrane (CEM), the acidic environment increases the rate of competing hydrogen evolution reaction (HER) over the formation of desired products by CO 2 RR. [11] Hence, it is necessary to maintain significantly different local pH environments at each electrode. The construction of bipolar membranes (BPM) with a cation exchange layer (CEL) and an anion exchange layer (AEL) is an approach to maintain different local pH environments at each electrode. [12] A modeling study addresses the issues of species transport, heat transfer, and the kinetics of all electrode and electrolyte reactions during CO 2 RR. [4] BPM design also eliminates the CO 2 "pump" effect which is obvious for AEMs. [6] In a reverse-biased (where ions are generated) BPM-based electrolyzer, the anionic and neutral products crossover is mitigated by the outward flux of H + and OH À ions towards the cathode and anode, respectively. [7] This crossover occurs by the electromigration of anionic products or via diffusion and electroosmosis of the neutral products. [7] Now, writing in the journal Nature Chemistry, [13] Thomas E. Mallouk and colleagues fabricated BPMs with a weak-acid cation exchange layer to suppress the evolution of H 2 by competing HER without hampering the desired product formation by CO 2 RR. The researchers fabricated a cell with a transparent quartz window at the cathode with a hole in the center of the gas diffusion layer (GDL) to see the physical changes on the membrane surface that can result in low Faradaic efficiency (FE) in the BPM-based CO 2 electrolyzer (Figure 1A). Although the overall cell current density of~80 mA/cm 2 was achieved, the FE of CO 2 electroreduction to CO was low because of the H 2 evolution by competing HER during cell operation (Figure 1B). The evolution of H 2 gas at the CEL surface of BPM was noticed in the optical images (Figure 1C). The formation of mild gas bubbles was identified at low cell potential (-2.5 V) whereas, at higher potential (-3.0 V) gas bubbles evolved vigorously (Fig-ure 1C). The gas bubbles were generated due to the low solubility of CO 2 in the aqueous microphase of the acidic CEL (Figure 1D). Under reverse bias, the H + produced at the AEL/ CEL interface of the BPM by the splitting of water migrates towards the cathode, and acids are generated. The acidic environment at the CEL/GDL region resulted in the formation of insoluble CO 2 species and bubbles are formed (Figure 1D). The authors adopted a novel strategy to fabricate BPM with layer-by-layer (LBL) assembly of polyelectrolytes to generate a weak-acid layer on strongly acidic CEL by exposing CEL to solutions of poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH). The BPM thus fabricated helped in suppressed HER without hampering CO 2 RR. The CO FE of LBL BPM was higher than that of the Nafion BPM, although CO current…
Anion exchange membrane fuel cells (AEMFCs) have been widely touted as a low-cost alternative to ... more Anion exchange membrane fuel cells (AEMFCs) have been widely touted as a low-cost alternative to existing proton exchange membrane fuel cells. However, AEMFCs operating on air suffer from a severe performance penalty caused by carbonation from exposure to CO2. Many approaches to removing CO2 from the cathode inlet would consume valuable energy and complicate the systems-level balance-of-plant. Therefore, this work focuses on an electrochemical solution where CO2 removal would still generate power, but not expose an entire AEMFC stack to carbonation conditions. Such a system consists of two AEMFCs in series. The first AEMFC, which acts as an anion exchange CO2 separator (AECS), is relatively small and serves to scrub CO2 from the air. The AECS is powered by the hydrogen bleed from the second (i.e., main) AEMFC. A small amount of hydrogen is bled from the recycled hydrogen used in the main AEMFC to mitigate impurity build-up, including nitrogen gas from diffusion across its membrane. ...
The production of H 2 has aroused considerable attention worldwide as a renewable and sustainable... more The production of H 2 has aroused considerable attention worldwide as a renewable and sustainable energy source for domestic, industrial, and automotive purposes. Currently, about 95 % of H 2 is produced from the steam reforming of methane. However, this process leads to the burning of fossil fuels and emits greenhouse gases into the atmosphere. Water electrolysis is an effective strategy to produce H 2 in high purity. Alkaline anion exchange membrane water electrolysis (AAEMWE) is preferred to proton exchange membrane water electrolysis (PEMWE) because of the flexibility to be able to use cheaper membranes as separators and non-noble electrocatalysts. However, the sluggish oxygen evolution reaction (OER) kinetics in AAEMWE is a bottleneck for water splitting efficiency and decreases the overall performances. Now, a novel nickel and iron graphene-nanoplatelets-supported metal-organic framework based electrocatalyst has been developed that shows excellent durability and record-high current density for alkaline electrolysis that outperforms the state-of-the-art OER electro-catalysts.
A series of previously synthesized homoleptic and heteroleptic complexes of zirconium and hafnium... more A series of previously synthesized homoleptic and heteroleptic complexes of zirconium and hafnium were used for the polymerization of ethylene. Upon activation with methylaluminoxane, all the complexes serve as pre-catalysts for the polymerization of ethylene. The effects of polymerization time, reaction temperature, solvents, and methylaluminoxane to catalyst ratio on the polyethylene yield were investigated. The catalyst activity depends on the coordination environment of the metals. The highest activity obtained was 5.91 × 104 g of polyethylene/[(mol of catalyst) h] under the optimized conditions of hexane as a solvent, reaction time and temperature of 30 min and 50°C respectively, and MAO to catalyst ratio of 1000 : 1.
The synthesis and characterization of novel homoleptic Ti and Zr complexes with tridentate ONO-ty... more The synthesis and characterization of novel homoleptic Ti and Zr complexes with tridentate ONO-type Schiff base ligands and their catalytic activities towards the ring-opening polymerization (ROP) of lactide are reported.
Green hydrogen produced through anion exchange membrane water electrolysis is a promising, low-co... more Green hydrogen produced through anion exchange membrane water electrolysis is a promising, low-cost chemical storage solution for intermittent renewable energy sources. Low-temperature electrolysis using anion exchange membranes (AEM) combines the benefits of established water electrolysis technologies based on alkaline electrolysis and proton exchange membrane electrolysis. The anion conductive ionomers (ACI) used in the AEM electrolyzer (AEMEL) electrodes has been investigated. The ACI serves two primary purposes: (i) facilitate hydroxide conduction between the catalyst and bulk electrolyte and (ii) bind the catalyst to the porous transport layer and membrane. High ion exchange capacity (IEC) ACIs are desired, however, high IEC can cause excessive water uptake (WU) and detrimental ACI swelling. Proper water management is a key factor in obtaining maximum performance in AEM-based devices. In this study, a series of poly(norbornene)-based ACIs were synthesized and deployed in hydrog...
A systematic comparison between random and block copolymer membrane properties showed the suitabi... more A systematic comparison between random and block copolymer membrane properties showed the suitability of random copolymer membranes.
Role of Water Molecules in Enabling Site Hopping and Vehicular Transport Mechanisms in Polynorbor... more Role of Water Molecules in Enabling Site Hopping and Vehicular Transport Mechanisms in Polynorbornene-based Anion Exchange Membrane Zhongyang Wang, ⸹ Ge Sun ， ⸹ Mrinmay Mandal, ‡, Paul A. Kohl, ‡, Juan de Pablo, ⸹ Shrayesh N. Patel, ⸹ and Paul F. Nealey ⸹ ‡ School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, 30332-0100, United States ⸹ Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA Ion exchange membranes are at the heart of electrochemical conversion and storage devices such as fuel cells 1, water electrolyzers 2, CO2 electrolyzers 3. redox flow batteries 4, and reverse electrodialysis 5. Anion exchange membrane fuel cells (AEMFCs) have attracted enormous attention as alternatives to replace perfluorinated, sulfonic acid-based proton exchange membrane fuel cells (PEMFCs) 6 because alkaline membrane electrode assemblies (MEAs) composed of anion exchange ionomers (AEIs) and AEMs that allow the use of Ni 7, 8, Fe 9, and Ag 10 based precious-group-metal (PGM) free catalysts in alkaline environments for hydrogen oxidation reactions (HORs) and oxygen reduction reactions (ORRs). However, the lack of understanding of ion transport mechanisms at different hydration levels of an anion exchange membrane hinders the rational design of the MEAs in an AEMFC. Here we investigate site hopping and vehicular transport mechanisms using anion exchange thin films, interdigitated electrodes, and atomistic molecular dynamics simulations. Halide ion (Br-, Cl- and I-) conductivities in polynorbornene-based thin films are measured as a function of temperature and relative humidity using electrochemical impedance spectroscopy. Halide ions show Arrhenius behaviors, and activation energy (Ea) is for the first time used as an indicator for detecting the transition of site hopping and vehicular transport mechanisms. Using atomistic molecular dynamics simulation, we quantitatively demonstrate that the transition of site hopping and vehicular mechanisms is aided by better solvation environments of anions and more percolated water pathways. References Z. Wang, J. Parrondo, C. He, S. Sankarasubramanian and V. Ramani, Nature Energy, 2019, 4, 281-289. S. Z. Oener, M. J. Foster and S. W. Boettcher, Science, 2020, 369, 1099-1103. D. A. Salvatore, C. M. Gabardo, A. Reyes, C. P. O’Brien, S. Holdcroft, P. Pintauro, B. Bahar, M. Hickner, C. Bae, D. Sinton, E. H. Sargent and C. P. Berlinguette, Nature Energy, 2021, 6, 339-348. K. Lin, Q. Chen, M. R. Gerhardt, L. Tong, S. B. Kim, L. Eisenach, A. W. Valle, D. Hardee, R. G. Gordon, M. J. Aziz and M. P. Marshak, Science, 2015, 349, 1529-1532. R. D. Cusick, Y. Kim and B. E. Logan, Science, 2012, 335, 1474-1477. J. Wang, Y. Zhao, B. P. Setzler, S. Rojas-Carbonell, C. Ben Yehuda, A. Amel, M. Page, L. Wang, K. Hu, L. Shi, S. Gottesfeld, B. Xu and Y. Yan, Nature Energy, 2019, 4, 392-398. G. Braesch, Z. Wang, S. Sankarasubramanian, A. G. Oshchepkov, A. Bonnefont, E. R. Savinova, V. Ramani and M. Chatenet, Journal of Materials Chemistry A, 2020, 8, 20543-20552. S. Kabir, K. Lemire, K. Artyushkova, A. Roy, M. Odgaard, D. Schlueter, A. Oshchepkov, A. Bonnefont, E. Savinova, D. C. Sabarirajan, P. Mandal, E. J. Crumlin, Iryna V. Zenyuk, P. Atanassov and A. Serov, Journal of Materials Chemistry A, 2017, 5, 24433-24443. H. Adabi, A. Shakouri, N. Ul Hassan, J. R. Varcoe, B. Zulevi, A. Serov, J. R. Regalbuto and W. E. Mustain, Nature Energy, 2021, 6, 834-843. H. Erikson, A. Sarapuu and K. Tammeveski, ChemElectroChem, 2019, 6, 73-86.
Anion exchange membrane fuel cells (AEMFCs) have recently shown excellent progress in terms of th... more Anion exchange membrane fuel cells (AEMFCs) have recently shown excellent progress in terms of their performance − e.g., achievable power and current density. However, very few AEMFCs have been demonstrated with the ability to operate for a long duration (>1000 h). In addition, it is unknown whether performance losses observed during operation are reversible, irreversible, or a combination of the two. In this study, a high-performance AEMFC operated continuously at 600 mA/cm 2 for 3600 h (150 days) at 80°C with H 2 /O 2 reacting gases was demonstrated. Throughout testing, the electrochemical properties of the AEMFC were probed to provide information about performance degradation pathways and their degree of reversibility. It was found that a portion of the performance loss that occurs during AEMFC operation was due to suboptimal reaction conditions and can be recovered. At the end of the experiment, the cell was disassembled, and its structure and composition were evaluated at the nanoscale by aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. The structure and composition of the electrode were compared to cells at the beginning of their operational life. It was found that the primary mechanism for long-term AEMFC performance loss was catalyst agglomeration. During the operational time, there was no evidence of significant polymer degradation, likely due to the high hydration state of the cell. By documenting the long-term changes in high-performing AEMFCs, this work provides important information for the systematic design of cell components and demonstrates the importance of controlling cell operation, which can aid in the commercialization and widespread deployment of low-cost, long-life AEMFCs.
Low-temperature water electrolysis using an anion conductive polymer electrolyte has several pote... more Low-temperature water electrolysis using an anion conductive polymer electrolyte has several potential advantages over other technologies, however, the fabrication of durable alkaline electrodes remains a challenge. Detachment of catalysts results in the loss of electrochemical surface area. Simple mixtures of ionomer and catalyst can suffer from poor catalyst adhesion because only physical adhesion is used to bind the components together. A family of chemically bonded, self-adherent, hydroxide conducting ionomers were synthesized and tested under alkaline electrolysis conditions with nickel ferrite anode electrocatalysts and platinum-nickel cathode catalyst. The ionomers are based on hydroxide conducting poly(norbornene) polymers used as the solid polymer electrolyte in alkaline fuel cells and electrolyzers. The synthesized terpolymer ionomers have been functionalized to provide pendant sites for covalent chemical bonding of bis(phenyl)-A-diglycidyl ether to the ionomer, catalyst, and porous transport layer. The electrodes show excellent adhesion between the catalyst particles, porous transport layer and ionomer, as determined by adhesion measurements and electrolysis performance. The AEM electrolyzer had stable voltage performance under high current density (1 A/ cm 2 at 1.83 V (67% voltage efficiency)) for extended time periods (>600 h) without degradation.
The behavior of the oxygen-evolving positive electrode (i.e. anode) in the anion exchange membran... more The behavior of the oxygen-evolving positive electrode (i.e. anode) in the anion exchange membrane water electrolyzer (AEMEL) is complex and influenced by several factors. Very few studies have been performed to understand oxygen evolution reaction (OER) behavior by optimizing the individual factors that influence performance. This study highlights the effects of catalyst loading, catalyst selection, porous transport layer (PTL) type and conductive additive content. The influence of each factor is elucidated through a design of experiments (DoE) approach with a full statistical analysis. Electrochemical data, alongside Pareto charts, parametric trends and their mutual interactions are discussed. This DoE approach is also helpful in making useful predictions and discovering new combinations to be tested. The end result was a high-performance AEMEL able to operate at a current density of 1.0 A/cm 2 at 1.80 V with IrOx OER and PtNi hydrogen evolution reaction (HER) catalysts using 0.3 M KOH fed to the anode. Even lower operating voltage was observed with PbRuOx catalyst at the anode, 1.64 V @ 1.0 A/cm 2 , though the cell decay rate was higher. Lastly, a IrOx/PtNi cell was stably operated continuously for 30 days (720 h) at 1.0 A/cm 2. This study can serve as a guide for optimal electrode design with insights into component-performance compromises, which can aid in making design choices and performing techno-economic analyses.
The cheaper and easy to handle catalysts are particularly important for catalytic studies. Herein... more The cheaper and easy to handle catalysts are particularly important for catalytic studies. Herein, inexpensive Co 2 O 3 and MnO 2 were used as catalysts for the ring-opening polymerization (ROP) of rac -lactide ( rac -LA) and ε- caprolactone ( ε -CL). The polymerization proceeded in a controlled manner with the formation of high molecular weight ( M n ) and narrow dispersity (Ð). Heterotactically enriched ( P r up to 0.7) poly(lactic acid) (PLA) was formed during the polymerization process. MALDI-TOF and 1 H NMR analyses of low M n oligomer from rac -LA indicated that the polymerization followed an activated monomer mechanism. The data on the polymerization kinetics showed that the polymerization followed first order kinetics.
CO 2 reduction reaction (CO 2 RR) is a promising way to convert CO 2 into value-added products. M... more CO 2 reduction reaction (CO 2 RR) is a promising way to convert CO 2 into value-added products. Membrane-based gas-phase CO 2 RR offers several advantages like high selectivity and energy efficiency. However, high product crossover and poor CO 2 utilization in anion exchange membranes (AEMs) prevents the utilization of AEMs for CO 2 RR. The acidic environment of the cation exchange membrane can negatively influence the CO 2 reduction reaction (CO 2 RR) activity by favoring the competing hydrogen evolution reaction (HER). Hence, it is necessary to manipulate the local pH environment of the electrodes to yield maximum productivity. Bipolar membranes (BPMs) with a cation exchange layer (CEL) and an anion exchange layer (AEL) help in maintaining different local pH environments at each electrode. Now, a bipolar membrane fabrication with a weak-acid cation exchange layer removes the possibility of competing HER without affecting CO 2 RR. The increasing demand for energy due to population growth and rapid industrialization results in extensive CO 2 emissions in the atmosphere. Renewable energy sources (such as solar cells and wind power) powered production of value-added chem-icals/fuels and storage of emission-free renewable energy by the electrocatalytic CO 2 reduction reaction (CO 2 RR) is a promising approach to mitigate the increased risk associated with the increase in CO 2 concentration in the atmosphere. [1,2] Aqueous-phase CO 2 RR offers low current density because of the low solubility and slow diffusion of CO 2 in aqueous media. [3] Gas-phase membrane-based CO 2 RR by constructing electrochemical cells consisting of a membrane electrode assembly (MEA) has shown higher product selectivity and energy efficiency. [3-6] In anion exchange membrane (AEM), the problems with high product crossover, poor CO 2 utilization, and low ionic conductivity in comparison to CEM prevent the widespread adoption of AEMs for CO 2 RR. [7] However, the problems with low ionic conductivity and poor alkaline stability are systematically addressed with the development of recent AEMs. [8-10] In cation exchange membrane (CEM), the acidic environment increases the rate of competing hydrogen evolution reaction (HER) over the formation of desired products by CO 2 RR. [11] Hence, it is necessary to maintain significantly different local pH environments at each electrode. The construction of bipolar membranes (BPM) with a cation exchange layer (CEL) and an anion exchange layer (AEL) is an approach to maintain different local pH environments at each electrode. [12] A modeling study addresses the issues of species transport, heat transfer, and the kinetics of all electrode and electrolyte reactions during CO 2 RR. [4] BPM design also eliminates the CO 2 "pump" effect which is obvious for AEMs. [6] In a reverse-biased (where ions are generated) BPM-based electrolyzer, the anionic and neutral products crossover is mitigated by the outward flux of H + and OH À ions towards the cathode and anode, respectively. [7] This crossover occurs by the electromigration of anionic products or via diffusion and electroosmosis of the neutral products. [7] Now, writing in the journal Nature Chemistry, [13] Thomas E. Mallouk and colleagues fabricated BPMs with a weak-acid cation exchange layer to suppress the evolution of H 2 by competing HER without hampering the desired product formation by CO 2 RR. The researchers fabricated a cell with a transparent quartz window at the cathode with a hole in the center of the gas diffusion layer (GDL) to see the physical changes on the membrane surface that can result in low Faradaic efficiency (FE) in the BPM-based CO 2 electrolyzer (Figure 1A). Although the overall cell current density of~80 mA/cm 2 was achieved, the FE of CO 2 electroreduction to CO was low because of the H 2 evolution by competing HER during cell operation (Figure 1B). The evolution of H 2 gas at the CEL surface of BPM was noticed in the optical images (Figure 1C). The formation of mild gas bubbles was identified at low cell potential (-2.5 V) whereas, at higher potential (-3.0 V) gas bubbles evolved vigorously (Fig-ure 1C). The gas bubbles were generated due to the low solubility of CO 2 in the aqueous microphase of the acidic CEL (Figure 1D). Under reverse bias, the H + produced at the AEL/ CEL interface of the BPM by the splitting of water migrates towards the cathode, and acids are generated. The acidic environment at the CEL/GDL region resulted in the formation of insoluble CO 2 species and bubbles are formed (Figure 1D). The authors adopted a novel strategy to fabricate BPM with layer-by-layer (LBL) assembly of polyelectrolytes to generate a weak-acid layer on strongly acidic CEL by exposing CEL to solutions of poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH). The BPM thus fabricated helped in suppressed HER without hampering CO 2 RR. The CO FE of LBL BPM was higher than that of the Nafion BPM, although CO current…
Anion exchange membrane fuel cells (AEMFCs) have been widely touted as a low-cost alternative to ... more Anion exchange membrane fuel cells (AEMFCs) have been widely touted as a low-cost alternative to existing proton exchange membrane fuel cells. However, AEMFCs operating on air suffer from a severe performance penalty caused by carbonation from exposure to CO2. Many approaches to removing CO2 from the cathode inlet would consume valuable energy and complicate the systems-level balance-of-plant. Therefore, this work focuses on an electrochemical solution where CO2 removal would still generate power, but not expose an entire AEMFC stack to carbonation conditions. Such a system consists of two AEMFCs in series. The first AEMFC, which acts as an anion exchange CO2 separator (AECS), is relatively small and serves to scrub CO2 from the air. The AECS is powered by the hydrogen bleed from the second (i.e., main) AEMFC. A small amount of hydrogen is bled from the recycled hydrogen used in the main AEMFC to mitigate impurity build-up, including nitrogen gas from diffusion across its membrane. ...
The production of H 2 has aroused considerable attention worldwide as a renewable and sustainable... more The production of H 2 has aroused considerable attention worldwide as a renewable and sustainable energy source for domestic, industrial, and automotive purposes. Currently, about 95 % of H 2 is produced from the steam reforming of methane. However, this process leads to the burning of fossil fuels and emits greenhouse gases into the atmosphere. Water electrolysis is an effective strategy to produce H 2 in high purity. Alkaline anion exchange membrane water electrolysis (AAEMWE) is preferred to proton exchange membrane water electrolysis (PEMWE) because of the flexibility to be able to use cheaper membranes as separators and non-noble electrocatalysts. However, the sluggish oxygen evolution reaction (OER) kinetics in AAEMWE is a bottleneck for water splitting efficiency and decreases the overall performances. Now, a novel nickel and iron graphene-nanoplatelets-supported metal-organic framework based electrocatalyst has been developed that shows excellent durability and record-high current density for alkaline electrolysis that outperforms the state-of-the-art OER electro-catalysts.
A series of previously synthesized homoleptic and heteroleptic complexes of zirconium and hafnium... more A series of previously synthesized homoleptic and heteroleptic complexes of zirconium and hafnium were used for the polymerization of ethylene. Upon activation with methylaluminoxane, all the complexes serve as pre-catalysts for the polymerization of ethylene. The effects of polymerization time, reaction temperature, solvents, and methylaluminoxane to catalyst ratio on the polyethylene yield were investigated. The catalyst activity depends on the coordination environment of the metals. The highest activity obtained was 5.91 × 104 g of polyethylene/[(mol of catalyst) h] under the optimized conditions of hexane as a solvent, reaction time and temperature of 30 min and 50°C respectively, and MAO to catalyst ratio of 1000 : 1.
The synthesis and characterization of novel homoleptic Ti and Zr complexes with tridentate ONO-ty... more The synthesis and characterization of novel homoleptic Ti and Zr complexes with tridentate ONO-type Schiff base ligands and their catalytic activities towards the ring-opening polymerization (ROP) of lactide are reported.
Green hydrogen produced through anion exchange membrane water electrolysis is a promising, low-co... more Green hydrogen produced through anion exchange membrane water electrolysis is a promising, low-cost chemical storage solution for intermittent renewable energy sources. Low-temperature electrolysis using anion exchange membranes (AEM) combines the benefits of established water electrolysis technologies based on alkaline electrolysis and proton exchange membrane electrolysis. The anion conductive ionomers (ACI) used in the AEM electrolyzer (AEMEL) electrodes has been investigated. The ACI serves two primary purposes: (i) facilitate hydroxide conduction between the catalyst and bulk electrolyte and (ii) bind the catalyst to the porous transport layer and membrane. High ion exchange capacity (IEC) ACIs are desired, however, high IEC can cause excessive water uptake (WU) and detrimental ACI swelling. Proper water management is a key factor in obtaining maximum performance in AEM-based devices. In this study, a series of poly(norbornene)-based ACIs were synthesized and deployed in hydrog...
A systematic comparison between random and block copolymer membrane properties showed the suitabi... more A systematic comparison between random and block copolymer membrane properties showed the suitability of random copolymer membranes.
Anion Exchange Membranes (AEM) can be used in fuel cells and electrolyzers. The benefits include ... more Anion Exchange Membranes (AEM) can be used in fuel cells and electrolyzers. The benefits include lowering the amount of platinum catalysts, simplifying water management, and improving electrochemical kinetics at the air cathode. However, the performance of AEMs has not as high as that of proton exchange membranes partially because of factors such as low ionic conductivity, poor stability at high pH, and high water uptake. A series of multiblock copolymers including poly(arylene ether)s and poly(norbornenes) with long head-group tether were synthesized for use in AEM fuel cells and electrolyzers. In this study, the number of head-groups per block and resulting conductivity, domain size and water uptake was studied. The improvement in performance (increased conductivity and reduced water uptake) was correlated with domain size, bound and unbound water content, and ion channel configuration.
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Papers by mrinmay mandal
A series of multiblock copolymers including poly(arylene ether)s and poly(norbornenes) with long head-group tether were synthesized for use in AEM fuel cells and electrolyzers. In this study, the number of head-groups per block and resulting conductivity, domain size and water uptake was studied. The improvement in performance (increased conductivity and reduced water uptake) was correlated with domain size, bound and unbound water content, and ion channel configuration.