As a choke point in water electrolysis,the oxygen evolution reaction(OER)suffers from the severe electrode polarization and large overpotential.Herein,the porous hierarchical hetero-(Nis Fe)FeN/Ni catalysts are in sit...As a choke point in water electrolysis,the oxygen evolution reaction(OER)suffers from the severe electrode polarization and large overpotential.Herein,the porous hierarchical hetero-(Nis Fe)FeN/Ni catalysts are in situ constructed for the eficient electrocatalytic OER.X-ray absorption fine structure characterizations reveal the strong Ni-Fe bimetallic interaction in(Niz Fex)FeN/Ni.Theoretical study indicates the heterojunction and bimetallic interaction decrease the free-energy change for the rate-limiting step of the OER and the overpotential thereof.In addition,the high conductivity and porous hierarchical morphology favor the electron transfer,electrolyte access and O2 release.Consequently,the optimized catalyst achieves a low overpotential of 223 mV at 10 mA.cm^-2,a small Tafel slope of 68 mV:dec^-1,and a high stability.The excellent performance of the optimized catalyst is also demonstrated by the overall water electrolysis with a low working voltage and high Faradaic efficiency.Moreover,the correlation between the structure and performance is well established by the experimental characterizations and theoretical calculations,which confirms the origin of the OER activity from the surface metal oxyhydroxide in situ generated upon applying the current.This study suggests a promising approach to the advanced OER electrocatalysts for practical applications by constructing the porous hierarchical metal-compound/metal heterojunctions.展开更多
The investigation of earth-abundant electrocatalysts for efficient water electrolysis is of central importance in renewable energy system, which is currently impeded by the large overpotential of oxygen evolution reac...The investigation of earth-abundant electrocatalysts for efficient water electrolysis is of central importance in renewable energy system, which is currently impeded by the large overpotential of oxygen evolution reaction (OER). NiFe sulfides show promising OER activity but are troubled by their low intrinsic conductivities. Herein, we demonstrate the construction of the porous core-shell heterojunctions of FeNi3@(Fe,Ni)S_(2) with tunable shell thickness via the reduction of hierarchical NiFe(OH)x nanosheets followed by a partial sulfidization. The conductive FeNi3 core provides the highway for electron transport, and the (Fe,Ni)S_(2) shell offers the exposed surface for in situ generation of S-doped NiFe-oxyhydroxides with high intrinsic OER activity, which is supported by the combined experimental and theoretical studies. In addition, the porous hierarchical morphology favors the electrolyte access and O_(2) liberation. Consequently, the optimized catalyst achieves an excellent OER performance with a low overpotential of 288 mV at 100 mA·cm^(−2), a small Tafel slope of 48 mV·dec^(−1), and a high OER durability for at least 1,200 h at 200 mA·cm^(−2). This study provides an effective way to explore the advanced earth-abundant OER electrocatalysts by constructing the heterojunctions between metal and corresponding metal-compounds via the convenient post treatment, such as nitridation and sulfidization.展开更多
Cobalt-based oxygenic compounds Co(OH)2,CoO and Co3 O4 are attractive for electrochemical energy storage owing to their high theoretical capacities and pseudocapacitive properties.Despite the great efforts to their co...Cobalt-based oxygenic compounds Co(OH)2,CoO and Co3 O4 are attractive for electrochemical energy storage owing to their high theoretical capacities and pseudocapacitive properties.Despite the great efforts to their compositional and morphological regulations,the performances to date are still quite limited owing to the low active surface area and sluggish charge transfer kinetics.Herein,different Co-based nanocrystals(Co-NCs)were conveniently anchored on the hierarchical nitrogen-doped carbon nanocages(hNCNCs)with high specific surface area and coexisting micro-meso-macropores to decrease the size and facilitate the charge transfer.Accordingly,a high specific capacity of1170 Fg^-1 is achieved at 2 Ag^-1 for the Co(OH)2/hNCNCs hybrid,in which the capacitance of Co(OH)2(2214 F gco(OH)2)is approaching to its theoretical maximum(2595 Fg^-1),demonstrating the high utilization of active materials by the hybridization with N-doped nanocarbons.This study also reveals that these Co-NCs store/release electrical energy via the same reversible redox reaction despite their different pristine compositions.This insight on the energy storage of Co-based nanomaterials suggests that the commonly-employed transformation of the Co-NCs from Co(OH)2 to CoO and Co3 O4 on carbon supports is unnecessary and even could be harmful to the energy storage performance.The result is instructive to develop high-energy-density electrodes from transition metal compounds.展开更多
The lithium-oxygen(Li-O_(2))battery is highly promising but suffers from poor cycling life,especially at high rates;hence,the need for high-efficient accelerating agents is crucial.Recently macrocyclic Fe-based redox ...The lithium-oxygen(Li-O_(2))battery is highly promising but suffers from poor cycling life,especially at high rates;hence,the need for high-efficient accelerating agents is crucial.Recently macrocyclic Fe-based redox mediators,such as iron(II)phthalocyanine(FePc)and heme,have been developed and anticipated to be ideal due to their bifunctional charge and superoxide shuttling capabilities.However,they still operate far below expectations,which could result from the low concentrations in electrolyte due to the strongπ-πinteraction at carbon cathode.Herein,the authors report a new type of nonmacrocyclic Fe-based redox mediators,iron(II)acetylacetonate[Fe(acac)2]and iron(II)glycinate[Fe(gly)2],which have weakπ-πinteraction with the carbon cathode,thus,remain at high concentrations in the electrolyte.The Fe(gly)2@Li-O_(2)battery reaches a long life of 321 cycles at 0.5 A g^(−1),which is much superior to the counterpart with the typical macrocyclic FePc,and particularly exhibits a long life of 167 cycles at 2.0 A g^(−1)and 136 cycles at ultrahigh 5.0 A g^(−1).This study demonstrates an efficient strategy to achieve a high-rate performance of Li-O_(2)batteries by developing nonmacrocyclic Fe-based redox mediators with high-efficient electron and superoxide shuttling.展开更多
Efficient,durable and economic electrocatalysts are crucial for commercializing water electrolysis technology.Herein,we report an advanced bifunctional electrocatalyst for alkaline water splitting by growing NiFe-laye...Efficient,durable and economic electrocatalysts are crucial for commercializing water electrolysis technology.Herein,we report an advanced bifunctional electrocatalyst for alkaline water splitting by growing NiFe-layered double hydroxide(NiFe-LDH)nanosheet arrays on the conductive NiMo-based nanorods deposited on Ni foam to form a three-dimensional(3D)architecture,which exhibits exceptional performances for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).In overall water splitting,only the low operation voltages of 1.45/1.61 V are required to reach the current density of 10/500 mA·cm^(-2),and the continuous water splitting at an industrial-level current density of 500 mA·cm^(-2) shows a negligible degradation(1.8%)of the cell voltage over 1000 h.The outstanding performance is ascribed to the synergism of the HER-active NiMo-based nanorods and the OER-active NiFe-LDH nanosheet arrays of the hybridized 3D architecture.Specifically,the dense NiFe-LDH nanosheet arrays enhance the local pH on cathode by retarding OH-diffusion and enlarge the electrochemically active surface area on anode,while the conductive NiMo-based nanorods on Ni foam much decrease the charge-transfer resistances of both electrodes.This study provides an efficient strategy to explore advanced bifunctional electrocatalysts for overall water splitting by rationally hybridizing HER-and OER-active components.展开更多
基金This work was jointly supported by the National Key Research and Development Program of China(Nos.2017YFA0206500 and 2018YFA0209103)the National Natural Science Foundation of China(Nos.21832003,21773111,51571110,and 21573107)the Fundamental Research Funds for the Central Universities(No.020514380126).
文摘As a choke point in water electrolysis,the oxygen evolution reaction(OER)suffers from the severe electrode polarization and large overpotential.Herein,the porous hierarchical hetero-(Nis Fe)FeN/Ni catalysts are in situ constructed for the eficient electrocatalytic OER.X-ray absorption fine structure characterizations reveal the strong Ni-Fe bimetallic interaction in(Niz Fex)FeN/Ni.Theoretical study indicates the heterojunction and bimetallic interaction decrease the free-energy change for the rate-limiting step of the OER and the overpotential thereof.In addition,the high conductivity and porous hierarchical morphology favor the electron transfer,electrolyte access and O2 release.Consequently,the optimized catalyst achieves a low overpotential of 223 mV at 10 mA.cm^-2,a small Tafel slope of 68 mV:dec^-1,and a high stability.The excellent performance of the optimized catalyst is also demonstrated by the overall water electrolysis with a low working voltage and high Faradaic efficiency.Moreover,the correlation between the structure and performance is well established by the experimental characterizations and theoretical calculations,which confirms the origin of the OER activity from the surface metal oxyhydroxide in situ generated upon applying the current.This study suggests a promising approach to the advanced OER electrocatalysts for practical applications by constructing the porous hierarchical metal-compound/metal heterojunctions.
基金This work was jointly supported by the National Key Research and Development Program of China (Nos. 2017YFA0206500 and 2018YFA0209103)the National Natural Science Foundation of China (Nos. 52071174, 21832003, 21773111, and 21972061)+1 种基金the Fundamental Research Funds for the Central Universities (No. 020514380126)The numerical calculations have been done on the computing facilities in the High Performance Computing Center (HPCC) of Nanjing University. We thank the staff of the BL14W1 beamline at Shanghai Synchrotron Radiation Facility for assistance with the X-ray absorption measurements.
文摘The investigation of earth-abundant electrocatalysts for efficient water electrolysis is of central importance in renewable energy system, which is currently impeded by the large overpotential of oxygen evolution reaction (OER). NiFe sulfides show promising OER activity but are troubled by their low intrinsic conductivities. Herein, we demonstrate the construction of the porous core-shell heterojunctions of FeNi3@(Fe,Ni)S_(2) with tunable shell thickness via the reduction of hierarchical NiFe(OH)x nanosheets followed by a partial sulfidization. The conductive FeNi3 core provides the highway for electron transport, and the (Fe,Ni)S_(2) shell offers the exposed surface for in situ generation of S-doped NiFe-oxyhydroxides with high intrinsic OER activity, which is supported by the combined experimental and theoretical studies. In addition, the porous hierarchical morphology favors the electrolyte access and O_(2) liberation. Consequently, the optimized catalyst achieves an excellent OER performance with a low overpotential of 288 mV at 100 mA·cm^(−2), a small Tafel slope of 48 mV·dec^(−1), and a high OER durability for at least 1,200 h at 200 mA·cm^(−2). This study provides an effective way to explore the advanced earth-abundant OER electrocatalysts by constructing the heterojunctions between metal and corresponding metal-compounds via the convenient post treatment, such as nitridation and sulfidization.
基金jointly supported by the National Key Research and Development Program of China(2017YFA0206500and 2018YFA0209103)the National Natural Science Foundation of China(21832003,21773111,51571110 and 21573107)the Fundamental Research Funds for the Central Universities(020514380126)
文摘Cobalt-based oxygenic compounds Co(OH)2,CoO and Co3 O4 are attractive for electrochemical energy storage owing to their high theoretical capacities and pseudocapacitive properties.Despite the great efforts to their compositional and morphological regulations,the performances to date are still quite limited owing to the low active surface area and sluggish charge transfer kinetics.Herein,different Co-based nanocrystals(Co-NCs)were conveniently anchored on the hierarchical nitrogen-doped carbon nanocages(hNCNCs)with high specific surface area and coexisting micro-meso-macropores to decrease the size and facilitate the charge transfer.Accordingly,a high specific capacity of1170 Fg^-1 is achieved at 2 Ag^-1 for the Co(OH)2/hNCNCs hybrid,in which the capacitance of Co(OH)2(2214 F gco(OH)2)is approaching to its theoretical maximum(2595 Fg^-1),demonstrating the high utilization of active materials by the hybridization with N-doped nanocarbons.This study also reveals that these Co-NCs store/release electrical energy via the same reversible redox reaction despite their different pristine compositions.This insight on the energy storage of Co-based nanomaterials suggests that the commonly-employed transformation of the Co-NCs from Co(OH)2 to CoO and Co3 O4 on carbon supports is unnecessary and even could be harmful to the energy storage performance.The result is instructive to develop high-energy-density electrodes from transition metal compounds.
基金This study was jointly financed by the National Key Research and Development Program of China(nos.2018YFA0209100 and 2017YFA0206500)the NSFC(nos.21832003,21972061,21773111,51571110,and 21573107)the Fundamental Research Funds for the Central Universities(no.14380237).
文摘The lithium-oxygen(Li-O_(2))battery is highly promising but suffers from poor cycling life,especially at high rates;hence,the need for high-efficient accelerating agents is crucial.Recently macrocyclic Fe-based redox mediators,such as iron(II)phthalocyanine(FePc)and heme,have been developed and anticipated to be ideal due to their bifunctional charge and superoxide shuttling capabilities.However,they still operate far below expectations,which could result from the low concentrations in electrolyte due to the strongπ-πinteraction at carbon cathode.Herein,the authors report a new type of nonmacrocyclic Fe-based redox mediators,iron(II)acetylacetonate[Fe(acac)2]and iron(II)glycinate[Fe(gly)2],which have weakπ-πinteraction with the carbon cathode,thus,remain at high concentrations in the electrolyte.The Fe(gly)2@Li-O_(2)battery reaches a long life of 321 cycles at 0.5 A g^(−1),which is much superior to the counterpart with the typical macrocyclic FePc,and particularly exhibits a long life of 167 cycles at 2.0 A g^(−1)and 136 cycles at ultrahigh 5.0 A g^(−1).This study demonstrates an efficient strategy to achieve a high-rate performance of Li-O_(2)batteries by developing nonmacrocyclic Fe-based redox mediators with high-efficient electron and superoxide shuttling.
基金supported by the National Key Research and Development Program of China(No.2021YFA1500900)the National Natural Science Foundation of China(Nos.52071174,21832003,21972061)+1 种基金the Natural Science Foundation of Jiangsu Province,Major Project(No.BK20212005)the Foundation of Science and Technology of Suzhou(No.SYC2022102).
文摘Efficient,durable and economic electrocatalysts are crucial for commercializing water electrolysis technology.Herein,we report an advanced bifunctional electrocatalyst for alkaline water splitting by growing NiFe-layered double hydroxide(NiFe-LDH)nanosheet arrays on the conductive NiMo-based nanorods deposited on Ni foam to form a three-dimensional(3D)architecture,which exhibits exceptional performances for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).In overall water splitting,only the low operation voltages of 1.45/1.61 V are required to reach the current density of 10/500 mA·cm^(-2),and the continuous water splitting at an industrial-level current density of 500 mA·cm^(-2) shows a negligible degradation(1.8%)of the cell voltage over 1000 h.The outstanding performance is ascribed to the synergism of the HER-active NiMo-based nanorods and the OER-active NiFe-LDH nanosheet arrays of the hybridized 3D architecture.Specifically,the dense NiFe-LDH nanosheet arrays enhance the local pH on cathode by retarding OH-diffusion and enlarge the electrochemically active surface area on anode,while the conductive NiMo-based nanorods on Ni foam much decrease the charge-transfer resistances of both electrodes.This study provides an efficient strategy to explore advanced bifunctional electrocatalysts for overall water splitting by rationally hybridizing HER-and OER-active components.
