Naoshad Islam

The development of low-Platinum content polymer electrolyte fuel cells (PEFCs) has been hindered by inexplicable reduction of oxygen reduction reaction (ORR) activity and unexpected O2 mass transport resistance when catalysts have been interfaced with ionomer in a cathode catalyst layer. In this study, we introduce a bottom-up designed spherical carbon support with intrinsic Nitrogen-doping that permits uniform dispersion of Pt catalyst, which reproducibly exhibits high ORR mass activity of 638 ± 68 mA mgPt−1 at 0.9 V and 100% relative humidity (RH) in a membrane electrode assembly. The uniformly distributed Nitrogen-functional surface groups on the carbon support surface promote high ionomer coverage directly evidenced by high-resolution electron microscopy and nearly humidity-independent double layer capacitance. The hydrophilic nature of the carbon surface appears to ensure high activity and performance for operation over a broad range of RH. The paradigm challenging large carbon...

The widespread adoption of polymer electrolyte fuel cell (PEFC) technology is currently limited by the challenges including catalyst activity, local O2-transport, catalyst durability, and water transport pertinent to high current density operation, specially at low Pt loaded electrodes. In addition to the development of new materials, meticulous understanding of the cathode components such as the catalyst layer (CL) and its constituent materials, and microporous layer (MPL) is required, which is difficult to achieve with the random and uncontrolled microstructure of conventional CL and MPL. This dissertation explores alternative cathode CL and MPL architectures guided by the known technical challenges limiting the wider commercialization of the PEFC technology on one hand and transport processes related scientific questions on the other hand. We introduced a new bottom-up designed spherical carbon support with intrinsic N-doping that permits uniform dispersion of Pt catalyst, which reproducibly exhibits record-high ORR mass activity at 0.9 V of ~ 0.6 A mgPt-1 at 100% relative humidity (RH) and ~ 1.0 A mgPt-1 at 60% RH, higher than any reported Pt catalyst in a membrane electrode assembly (MEA). The uniformly distributed N-functional surface groups on the carbon support surface promotes high ionomer coverage directly evidenced from high-resolution electron microscopy and nearly humidity-independent double layer capacitance. The hydrophilic nature of the carbon surface appears to ensure high activity and performance over a broad RH operation. The paradigm challenging large carbon support (~ 135 nm) combined with favorable ionomer film structure, hypothesized recently to arise from the interactions of ionic moiety of ionomer and N-functional group of the catalyst support, results in an unprecedented low oxygen transport resistance for ultra-low Pt loading (36 gPt cm-2). This thesis also introduced a model PEFC CL architecture by incorporating an electrocatalyst and an ionomer into nanoporous carbon scaffold (NCS – [...]

We introduce a novel self-standing, nanoporous carbon scaffold (NCS, 25 μm thick), with ordered inverse opal pore structure (~ 85 nm pore) as a microporous layer (MPL) in a polymer electrolyte membrane fuel cell (PEFC). Unlike previous studies, through chemical functionalization of the pore surfaces, the wettability of the MPL is controllably modified without altering the pore structure. Ex-situ environmental scanning electron microscopy experiments revealed water sorption in hydrophilic NCS at moderate relative humidity (RH) conditions but not in hydrophobic NCS, wherein water condensation on the surface was noted only at high RH. The influence of structure and wettability of different MPLs on cell performance was gleaned from steady-state cell polarization behavior. For cells operated at dry conditions (≤ 80% RH), the limiting current for cells with hydrophilic NCS MPL was the highest while that for cells with hydrophobic NCS MPL was lowest regardless of the level of water saturation (RH). Hydrophilic NCS pore surface enabled effective water removal via wicking like behavior while leaving pores open for gaseous transport at moderate RH (60-80%), whereas the hydrophobic NCS prevented facile liquid water transport, leading to water buildup in the catalyst layer (CL) and at the CL/MPL interface.

The microporous layer (MPL) is a key component of the membrane electrode assembly (MEA) of a polymer electrolyte membrane fuel cell (PEMFC). Historically, the MPL has been prepared by applying a slurry of carbon particles and Teflon onto the carbon paper. Together, the carbon paper with the MPL on it is known as the gas diffusion layer. The MPL fabricated by the aforementioned method results in a random pore structure varying both in pore size (ranging 20-200 nm) and wettability (hydrophobic and hydrophilic). Although the primary role of the MPL is thought to improve water management, delineation of the effect of pore size from wettability becomes difficult in a physically and chemically heterogenous porous structure of a conventional MPL. Recently, the Birss group has developed nanoporous carbon scaffolds (NCS) with an inverse opal structure that has well-defined and tunable pore sizes. The wettability of the internal surface of the NCS films can also be altered by functionalizatio...

ABSTRACT Atom transfer radical polymerization of vinyl pivalate was carried out in supercritical carbon dioxide using CuBr or CuCl/terpyridine (tpy) complex system and ethyl 2-bromoisobutyrate as an initiator. The reaction kinetics of the two different catalytic systems (CuBr/tpy and CuCl/tpy) was investigated. In addition, the effects of temperature, pressure, and catalyst/ligand concentration were examined systematically to obtain an acceptable rate of polymerization and control over the number-average molecular weight (Mn) and polydispersity index (PDI). The result showed that relatively low PDIs were obtained and polymerization rates were enhanced at higher pressures. The CuCl/tpy complex exhibited the maximum conversion of 90% with a Mn and PDI of 60.2 kg/mol and 1.29, respectively. The CuCl/tpy catalyst system showed better agreement between theoretical and experimental Mn compared to the CuBr/tpy. The living character of poly(vinyl pivalate) (PVPi) was proven by 1H NMR spectrum and chain extension reaction. The formation of poly(vinyl alcohol) via saponification of the resulting PVPi was also carried out. The structures of both PVPi and PVA were examined by 1H NMR and FTIR spectra.

Catalyst layer (CL) ionomers control several transport and interfacial phenomena including long-range transport of protons, local transport of oxygen to Pt catalyst, effective utilization of Pt catalyst, electrochemical reaction kinetics and double-layer capacitance. In this work, the variation of these properties, as a function of humidity, for CLs made with two ionomers differing in side-chain length and equivalent weight, Nafion-1100 and Aquivion-825, was investigated. This is the first study to examine humidity-dependent oxygen reduction reaction (ORR) kinetics in-situ for CLs with different ionomers. A significant finding is the observation of higher ORR kinetic activity (A/cm2Pt) for the Aquivion-825 CL than for the Nafion-1100 CL. This is attributed to differences in the interfacial protonic concentrations at Pt/ionomer interface in the two CLs. The differences in Pt/ionomer interface is also noted in a higher local oxygen transport resistance for Aquivion-825 CLs compared to...

Atom transfer radical polymerization of vinyl pivalate was carried out in supercritical carbon dioxide using CuBr or CuCl/terpyridine (tpy) complex system and ethyl 2-bromoisobutyrate as an initiator. The reaction kinetics of the two different catalytic systems (CuBr/tpy and CuCl/tpy) was investigated. In addition, the effects of temperature, pressure, and catalyst/ligand concentration were examined systematically to obtain an acceptable rate of polymerization and control over the number-average molecular weight (Mn) and polydispersity index (PDI). The result showed that relatively low PDIs were obtained and polymerization rates were enhanced at higher pressures. The CuCl/tpy complex exhibited the maximum conversion of 90% with a Mn and PDI of 60.2 kg/mol and 1.29, respectively. The CuCl/tpy catalyst system showed better agreement between theoretical and experimental Mn compared to the CuBr/tpy. The living character of poly(vinyl pivalate) (PVPi) was proven by 1H NMR spectrum and chain extension reaction. The formation of poly(vinyl alcohol) via saponification of the resulting PVPi was also carried out. The structures of both PVPi and PVA were examined by 1H NMR and FTIR spectra.