Introducing amorphous and ultrathin nanosheets of transition bimetal phosphate arrays that are hi... more Introducing amorphous and ultrathin nanosheets of transition bimetal phosphate arrays that are highly active in the oxygen evolution reaction (OER) as shells over an electronically modulated crystalline core with low hydrogen absorption energy for an excellent hydrogen evolution reaction (HER) can boost the sluggish kinetics of the OER and HER in alkaline electrolytes. Therefore, in this study, ultrathin and amorphous cobalt‐nickel‐phosphate (CoNiPOx) nanosheet arrays are deposited over vanadium (V)‐doped cobalt‐nitride (V3%‐Co4N) crystalline core nanowires to obtain amorphous‐shell@crystalline‐core mesoporous 3D‐heterostructures (CoNiPOx@V‐Co4N/NF) as bifunctional electrocatalysts. The optimized electrocatalyst shows extremely low HER and OER overpotentials of 53 and 270 mV at 10 mA cm−2, respectively. The CoNiPOx@V3%‐Co4N/NF (+/−) electrolyzer utilizing the electrocatalyst as both anode and cathode demonstrates remarkable overall water‐splitting activity, requiring a cell potential of only 1.52 V at 10 mA cm−2, 30 mV lower than that of the RuO2/NF (+)/20%‐Pt/C/NF (−) electrolyzer. Such impressive bifunctional activities can be attributed to abundant active sites, adjusted electronic structure, lower charge‐transfer resistance, enhanced electrochemically active surface area (ECSA), and surface‐ and volume‐confined electrocatalysis resulting from the synergistic effects of the crystalline V3%‐Co4N core and amorphous CoNiPOx shells boosting water splitting in alkaline media.
Heteroatom‐doped transition metal‐oxides of high oxygen evolution reaction (OER) activities inter... more Heteroatom‐doped transition metal‐oxides of high oxygen evolution reaction (OER) activities interfaced with metals of low hydrogen adsorption energy barrier for efficient hydrogen evolution reaction (HER) when uniformly embedded in a conductive nitrogen‐doped carbon (NC) matrix, can mitigate the low‐conductivity and high‐agglomeration of metal‐nanoparticles in carbon matrix and enhances their bifunctional activities. Thus, a 3D mesoporous heterostructure of boron (B)‐doped cobalt‐oxide/cobalt‐metal nanohybrids embedded in NC and grown on a Ni foam substrate (B‐CoO/Co@NC/NF) is developed as a binder‐free bifunctional electrocatalyst for alkaline water‐splitting via a post‐synthetic modification of the metal–organic framework and subsequent annealing in different Ar/H2 gas ratios. B‐CoO/Co@NC/NF prepared using 10% H2 gas (B‐CoO/Co@NC/NF [10% H2]) shows the lowest HER overpotential (196 mV) and B‐CoO/Co@NC/NF (Ar), developed in Ar, shows an OER overpotential of 307 mV at 10 mA cm−2 with excellent long‐term durability for 100 h. The best anode and cathode electrocatalyst‐based electrolyzer (B‐CoO/Co@NC/NF (Ar)(+)//B‐CoO/Co@NC/NF (10% H2)(−)) generates a current density of 10 mA cm−2 with only 1.62 V with long‐term stability. Further, density functional theory investigations demonstrate the effect of B‐doping on electronic structure and reaction mechanism of the electrocatalysts for optimal interaction with reaction intermediates for efficient alkaline water‐splitting which corroborates the experimental results.
The judicious design of highly electrochemically active materials on 1D fiber substrate to form a... more The judicious design of highly electrochemically active materials on 1D fiber substrate to form a hierarchical integrated hybrid structure is an efficient technique to improve the limited cylindrical space and volumetric energy density of fiber‐shaped supercapacitors (FSCs). Herein, a 3D negative electrode, consisting of vertically aligned interconnected mesoporous Co‐N/C leaf‐like structure on 1D MXene‐carbon fiber (Co‐N/C@MX/CF) is prepared by controlling the composition and morphology. At the same time, a 3D positive electrode is also prepared by introducing Mo in NiCo‐LDH anchored on Co‐N/C@MX/CF (Mo‐NiCo‐LDH@Co‐N/C@MX/CF) by electrodeposition method. Benefitting from the systematic hierarchical structures with highly accessible surface area, adequate pore size and easy permeation of electrolyte, both positive and negative electrodes demonstrate highly improved electrochemical performance with areal capacity/capacitance of 0.96 mAh cm−2/4.55 mF cm−2 at a current density of 3.86 ...
Heteroatom‐doped transition metal‐oxides of high oxygen evolution reaction (OER) activities inter... more Heteroatom‐doped transition metal‐oxides of high oxygen evolution reaction (OER) activities interfaced with metals of low hydrogen adsorption energy barrier for efficient hydrogen evolution reaction (HER) when uniformly embedded in a conductive nitrogen‐doped carbon (NC) matrix, can mitigate the low‐conductivity and high‐agglomeration of metal‐nanoparticles in carbon matrix and enhances their bifunctional activities. Thus, a 3D mesoporous heterostructure of boron (B)‐doped cobalt‐oxide/cobalt‐metal nanohybrids embedded in NC and grown on a Ni foam substrate (B‐CoO/Co@NC/NF) is developed as a binder‐free bifunctional electrocatalyst for alkaline water‐splitting via a post‐synthetic modification of the metal–organic framework and subsequent annealing in different Ar/H2 gas ratios. B‐CoO/Co@NC/NF prepared using 10% H2 gas (B‐CoO/Co@NC/NF [10% H2]) shows the lowest HER overpotential (196 mV) and B‐CoO/Co@NC/NF (Ar), developed in Ar, shows an OER overpotential of 307 mV at 10 mA cm−2 wit...
This review presents comprehensive details on recent developments in the fabrication of different... more This review presents comprehensive details on recent developments in the fabrication of different amorphous–crystalline heterostructures, their compositions, and the resulting physicochemical properties for OER, HER, and overall water splitting.
Additional file 1: Table. S1 Amount of ascorbic acid and hydroquinone used when mixing reducing a... more Additional file 1: Table. S1 Amount of ascorbic acid and hydroquinone used when mixing reducing agent. Fig. S1 (a–c) TEM images and average of (d) length, (e) diameter, and (f) aspect ratio when the volume of ascorbic acid is 30, 70, 90 uL. Fig. S2 (a–c) TEM images and average of (d) length, (e) diameter, and (f) aspect ratio when the volume of hydroquinone is 300, 700, 1500 uL.
The seed-mediated method is a general procedure for the synthesis of gold nanorods (Au NRs), and ... more The seed-mediated method is a general procedure for the synthesis of gold nanorods (Au NRs), and reducing agents such as ascorbic acid (AA) and hydroquinone (HQ) are widely used for the growth process. Further, they are mild reducing agents; however, when AA is used, controlling the size of Au NRs with a higher aspect ratio (localized surface plasmon resonance (LSPR) peak, λLmax > 900 nm) is challenging because it results in a faster growth rate of Au NRs. In contrast, when HQ is used, Au NRs with a higher aspect ratio can be synthesized as it slows down the growth rate of the Au NRs and greatly enhanced the λLmax. However, the increase in λLmax is still needs not satisfactory due to the limited enhancement in the aspect ratio of Au NRs due to utilization of single reducing agent. The growth kinetics of the Au NRs can be modulated by controlling the reducing power of the reducing agents. In such scenario, judicious use of two reducing agents such as AA and HQ simultaneously can h...
Introducing defects and in situ topotactic transformation of the electrocatalysts generating hete... more Introducing defects and in situ topotactic transformation of the electrocatalysts generating heterostructures of mixed-metal oxides(hydroxides) that are highly active for oxygen evolution reaction (OER) in tandem with metals of low hydrogen adsorption barrier for efficient hydrogen evolution reaction (HER) is urgently demanded for boosting the sluggish OER and HER kinetics in alkaline media. Ascertaining that, metal-organic-framework-derived freestanding, defect-rich, and in situ oxidized Fe-Co-O/Co metal@N-doped carbon (Co@NC) mesoporous nanosheet (mNS) heterostructure on Ni foam (Fe-Co-O/Co@NC-mNS/NF) is developed from the in situ oxidation of micropillar-like heterostructured Fe-Co-O/Co@NC/NF precatalyst. The in situ oxidized Fe-Co-O/Co@NC-mNS/NF exhibits excellent bifunctional properties by demanding only low overpotentials of 257 and 112 mV, respectively, for OER and HER at the current density of 10 mA cm-2 , with long-term durability, attributed to the existence of oxygen vacancies, higher specific surface area, increased electrochemical active surface area, and in situ generated new metal (oxyhydr)oxide phases. Further, Fe-Co-O/Co@NC-mNS/NF (+/-) electrolyzer requires only a low cell potential of 1.58 V to derive a current density of 10 mA cm-2 . Thus, the present work opens a new window for boosting the overall alkaline water splitting.
Hollow-structured Fex Co2-x P, Fex Co3-x O4 , and Prussian blue analogue (FeCo-PBA) microbuilding... more Hollow-structured Fex Co2-x P, Fex Co3-x O4 , and Prussian blue analogue (FeCo-PBA) microbuilding arrays on Ni foam (NF) are derived from Co-based metal-organic frameworks (Co-MOF) using a simple room temperature and post-heat-treatment route. Among them, Fex Co2-x P/NF shows excellent bifunctional catalytic activities by demonstrating very low oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) overpotentials of 255/114 mV at a current density of 20/10 mA cm-2 respectively, whereas Fex Co3-x O4 /NF and FeCo-PBA/NF demand higher overpotentials. Remarkably, for water electrolysis, Fex Co2-x P/NF requires only 1.61 V to obtain 10 mA cm-2 . In contrast to water electrolysis, urea electrolysis reduces overpotential and simultaneously purifies the urea-rich wastewater. The urea oxidation reaction at the Fex Co2-x P/NF anode needs just 1.345 V to achieve 20 mA cm-2 , which is 140 mV less than the 1.48 V potential required for OER. Moreover, the generation of H2 through urea electrolysis needs only 1.42 V to drive 10 mA cm-2 .
Transparent and flexible energy-storage devices have currently gained a lot of attention as weara... more Transparent and flexible energy-storage devices have currently gained a lot of attention as wearable and portable electronics. Herein, we develop a one-step electrodeposited MoS2 nanosheet@Ni-mesh core–shell network nanostructure as a transparent negative electrode for the flexible and transparent asymmetric solid-state supercapacitor (FT-ASSc). In the fabricated core–shell nanosheet network architecture, the junctionless interconnected Ni-mesh network with excellent conductivity contributes to superior electron transport pathways, and the nanostructure of the MoS2 over the Ni-mesh provides effective interface contact between the active material and current collector. As a result, the MoS2@Ni-mesh network negative electrode provides an areal capacitance of 7.31 mF cm−2 at the scan rate of 10 mV s−1 with an 80% capacity retention rate after 5000 GCD cycles. Moreover, the fabricated FT-ASSc with a transmittance of 51% can operate up to a maximum working potential window of 1.6 V and also provide a maximum volumetric capacitance of 48.32 mF cm−3 at 0.4 mA cm−3 current density. This work might provide a new strategy for improving the electrochemical performance of transparent and flexible energy-storage devices for next-generation integrated electronic gadgets.
Fabrication of 1T-Ni0.2Mo0.8S1.8P0.2 nanoflowers and 1T-Ni0.2Mo0.8S1.8P0.2 freestanding nanosheet... more Fabrication of 1T-Ni0.2Mo0.8S1.8P0.2 nanoflowers and 1T-Ni0.2Mo0.8S1.8P0.2 freestanding nanosheets with active basal planes and expanded interlayers as superior bifunctional electrocatalysts for water splitting.
Introducing amorphous and ultrathin nanosheets of transition bimetal phosphate arrays that are hi... more Introducing amorphous and ultrathin nanosheets of transition bimetal phosphate arrays that are highly active in the oxygen evolution reaction (OER) as shells over an electronically modulated crystalline core with low hydrogen absorption energy for an excellent hydrogen evolution reaction (HER) can boost the sluggish kinetics of the OER and HER in alkaline electrolytes. Therefore, in this study, ultrathin and amorphous cobalt‐nickel‐phosphate (CoNiPOx) nanosheet arrays are deposited over vanadium (V)‐doped cobalt‐nitride (V3%‐Co4N) crystalline core nanowires to obtain amorphous‐shell@crystalline‐core mesoporous 3D‐heterostructures (CoNiPOx@V‐Co4N/NF) as bifunctional electrocatalysts. The optimized electrocatalyst shows extremely low HER and OER overpotentials of 53 and 270 mV at 10 mA cm−2, respectively. The CoNiPOx@V3%‐Co4N/NF (+/−) electrolyzer utilizing the electrocatalyst as both anode and cathode demonstrates remarkable overall water‐splitting activity, requiring a cell potential of only 1.52 V at 10 mA cm−2, 30 mV lower than that of the RuO2/NF (+)/20%‐Pt/C/NF (−) electrolyzer. Such impressive bifunctional activities can be attributed to abundant active sites, adjusted electronic structure, lower charge‐transfer resistance, enhanced electrochemically active surface area (ECSA), and surface‐ and volume‐confined electrocatalysis resulting from the synergistic effects of the crystalline V3%‐Co4N core and amorphous CoNiPOx shells boosting water splitting in alkaline media.
Heteroatom‐doped transition metal‐oxides of high oxygen evolution reaction (OER) activities inter... more Heteroatom‐doped transition metal‐oxides of high oxygen evolution reaction (OER) activities interfaced with metals of low hydrogen adsorption energy barrier for efficient hydrogen evolution reaction (HER) when uniformly embedded in a conductive nitrogen‐doped carbon (NC) matrix, can mitigate the low‐conductivity and high‐agglomeration of metal‐nanoparticles in carbon matrix and enhances their bifunctional activities. Thus, a 3D mesoporous heterostructure of boron (B)‐doped cobalt‐oxide/cobalt‐metal nanohybrids embedded in NC and grown on a Ni foam substrate (B‐CoO/Co@NC/NF) is developed as a binder‐free bifunctional electrocatalyst for alkaline water‐splitting via a post‐synthetic modification of the metal–organic framework and subsequent annealing in different Ar/H2 gas ratios. B‐CoO/Co@NC/NF prepared using 10% H2 gas (B‐CoO/Co@NC/NF [10% H2]) shows the lowest HER overpotential (196 mV) and B‐CoO/Co@NC/NF (Ar), developed in Ar, shows an OER overpotential of 307 mV at 10 mA cm−2 with excellent long‐term durability for 100 h. The best anode and cathode electrocatalyst‐based electrolyzer (B‐CoO/Co@NC/NF (Ar)(+)//B‐CoO/Co@NC/NF (10% H2)(−)) generates a current density of 10 mA cm−2 with only 1.62 V with long‐term stability. Further, density functional theory investigations demonstrate the effect of B‐doping on electronic structure and reaction mechanism of the electrocatalysts for optimal interaction with reaction intermediates for efficient alkaline water‐splitting which corroborates the experimental results.
The judicious design of highly electrochemically active materials on 1D fiber substrate to form a... more The judicious design of highly electrochemically active materials on 1D fiber substrate to form a hierarchical integrated hybrid structure is an efficient technique to improve the limited cylindrical space and volumetric energy density of fiber‐shaped supercapacitors (FSCs). Herein, a 3D negative electrode, consisting of vertically aligned interconnected mesoporous Co‐N/C leaf‐like structure on 1D MXene‐carbon fiber (Co‐N/C@MX/CF) is prepared by controlling the composition and morphology. At the same time, a 3D positive electrode is also prepared by introducing Mo in NiCo‐LDH anchored on Co‐N/C@MX/CF (Mo‐NiCo‐LDH@Co‐N/C@MX/CF) by electrodeposition method. Benefitting from the systematic hierarchical structures with highly accessible surface area, adequate pore size and easy permeation of electrolyte, both positive and negative electrodes demonstrate highly improved electrochemical performance with areal capacity/capacitance of 0.96 mAh cm−2/4.55 mF cm−2 at a current density of 3.86 ...
Heteroatom‐doped transition metal‐oxides of high oxygen evolution reaction (OER) activities inter... more Heteroatom‐doped transition metal‐oxides of high oxygen evolution reaction (OER) activities interfaced with metals of low hydrogen adsorption energy barrier for efficient hydrogen evolution reaction (HER) when uniformly embedded in a conductive nitrogen‐doped carbon (NC) matrix, can mitigate the low‐conductivity and high‐agglomeration of metal‐nanoparticles in carbon matrix and enhances their bifunctional activities. Thus, a 3D mesoporous heterostructure of boron (B)‐doped cobalt‐oxide/cobalt‐metal nanohybrids embedded in NC and grown on a Ni foam substrate (B‐CoO/Co@NC/NF) is developed as a binder‐free bifunctional electrocatalyst for alkaline water‐splitting via a post‐synthetic modification of the metal–organic framework and subsequent annealing in different Ar/H2 gas ratios. B‐CoO/Co@NC/NF prepared using 10% H2 gas (B‐CoO/Co@NC/NF [10% H2]) shows the lowest HER overpotential (196 mV) and B‐CoO/Co@NC/NF (Ar), developed in Ar, shows an OER overpotential of 307 mV at 10 mA cm−2 wit...
This review presents comprehensive details on recent developments in the fabrication of different... more This review presents comprehensive details on recent developments in the fabrication of different amorphous–crystalline heterostructures, their compositions, and the resulting physicochemical properties for OER, HER, and overall water splitting.
Additional file 1: Table. S1 Amount of ascorbic acid and hydroquinone used when mixing reducing a... more Additional file 1: Table. S1 Amount of ascorbic acid and hydroquinone used when mixing reducing agent. Fig. S1 (a–c) TEM images and average of (d) length, (e) diameter, and (f) aspect ratio when the volume of ascorbic acid is 30, 70, 90 uL. Fig. S2 (a–c) TEM images and average of (d) length, (e) diameter, and (f) aspect ratio when the volume of hydroquinone is 300, 700, 1500 uL.
The seed-mediated method is a general procedure for the synthesis of gold nanorods (Au NRs), and ... more The seed-mediated method is a general procedure for the synthesis of gold nanorods (Au NRs), and reducing agents such as ascorbic acid (AA) and hydroquinone (HQ) are widely used for the growth process. Further, they are mild reducing agents; however, when AA is used, controlling the size of Au NRs with a higher aspect ratio (localized surface plasmon resonance (LSPR) peak, λLmax > 900 nm) is challenging because it results in a faster growth rate of Au NRs. In contrast, when HQ is used, Au NRs with a higher aspect ratio can be synthesized as it slows down the growth rate of the Au NRs and greatly enhanced the λLmax. However, the increase in λLmax is still needs not satisfactory due to the limited enhancement in the aspect ratio of Au NRs due to utilization of single reducing agent. The growth kinetics of the Au NRs can be modulated by controlling the reducing power of the reducing agents. In such scenario, judicious use of two reducing agents such as AA and HQ simultaneously can h...
Introducing defects and in situ topotactic transformation of the electrocatalysts generating hete... more Introducing defects and in situ topotactic transformation of the electrocatalysts generating heterostructures of mixed-metal oxides(hydroxides) that are highly active for oxygen evolution reaction (OER) in tandem with metals of low hydrogen adsorption barrier for efficient hydrogen evolution reaction (HER) is urgently demanded for boosting the sluggish OER and HER kinetics in alkaline media. Ascertaining that, metal-organic-framework-derived freestanding, defect-rich, and in situ oxidized Fe-Co-O/Co metal@N-doped carbon (Co@NC) mesoporous nanosheet (mNS) heterostructure on Ni foam (Fe-Co-O/Co@NC-mNS/NF) is developed from the in situ oxidation of micropillar-like heterostructured Fe-Co-O/Co@NC/NF precatalyst. The in situ oxidized Fe-Co-O/Co@NC-mNS/NF exhibits excellent bifunctional properties by demanding only low overpotentials of 257 and 112 mV, respectively, for OER and HER at the current density of 10 mA cm-2 , with long-term durability, attributed to the existence of oxygen vacancies, higher specific surface area, increased electrochemical active surface area, and in situ generated new metal (oxyhydr)oxide phases. Further, Fe-Co-O/Co@NC-mNS/NF (+/-) electrolyzer requires only a low cell potential of 1.58 V to derive a current density of 10 mA cm-2 . Thus, the present work opens a new window for boosting the overall alkaline water splitting.
Hollow-structured Fex Co2-x P, Fex Co3-x O4 , and Prussian blue analogue (FeCo-PBA) microbuilding... more Hollow-structured Fex Co2-x P, Fex Co3-x O4 , and Prussian blue analogue (FeCo-PBA) microbuilding arrays on Ni foam (NF) are derived from Co-based metal-organic frameworks (Co-MOF) using a simple room temperature and post-heat-treatment route. Among them, Fex Co2-x P/NF shows excellent bifunctional catalytic activities by demonstrating very low oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) overpotentials of 255/114 mV at a current density of 20/10 mA cm-2 respectively, whereas Fex Co3-x O4 /NF and FeCo-PBA/NF demand higher overpotentials. Remarkably, for water electrolysis, Fex Co2-x P/NF requires only 1.61 V to obtain 10 mA cm-2 . In contrast to water electrolysis, urea electrolysis reduces overpotential and simultaneously purifies the urea-rich wastewater. The urea oxidation reaction at the Fex Co2-x P/NF anode needs just 1.345 V to achieve 20 mA cm-2 , which is 140 mV less than the 1.48 V potential required for OER. Moreover, the generation of H2 through urea electrolysis needs only 1.42 V to drive 10 mA cm-2 .
Transparent and flexible energy-storage devices have currently gained a lot of attention as weara... more Transparent and flexible energy-storage devices have currently gained a lot of attention as wearable and portable electronics. Herein, we develop a one-step electrodeposited MoS2 nanosheet@Ni-mesh core–shell network nanostructure as a transparent negative electrode for the flexible and transparent asymmetric solid-state supercapacitor (FT-ASSc). In the fabricated core–shell nanosheet network architecture, the junctionless interconnected Ni-mesh network with excellent conductivity contributes to superior electron transport pathways, and the nanostructure of the MoS2 over the Ni-mesh provides effective interface contact between the active material and current collector. As a result, the MoS2@Ni-mesh network negative electrode provides an areal capacitance of 7.31 mF cm−2 at the scan rate of 10 mV s−1 with an 80% capacity retention rate after 5000 GCD cycles. Moreover, the fabricated FT-ASSc with a transmittance of 51% can operate up to a maximum working potential window of 1.6 V and also provide a maximum volumetric capacitance of 48.32 mF cm−3 at 0.4 mA cm−3 current density. This work might provide a new strategy for improving the electrochemical performance of transparent and flexible energy-storage devices for next-generation integrated electronic gadgets.
Fabrication of 1T-Ni0.2Mo0.8S1.8P0.2 nanoflowers and 1T-Ni0.2Mo0.8S1.8P0.2 freestanding nanosheet... more Fabrication of 1T-Ni0.2Mo0.8S1.8P0.2 nanoflowers and 1T-Ni0.2Mo0.8S1.8P0.2 freestanding nanosheets with active basal planes and expanded interlayers as superior bifunctional electrocatalysts for water splitting.
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