Storing solar energy in battery systems is crucial to achieving a green and sustainable society.However,the efficient development of photo-enhanced zinc-air batteries(ZABs)is limited by the rapid recombination of phot...Storing solar energy in battery systems is crucial to achieving a green and sustainable society.However,the efficient development of photo-enhanced zinc-air batteries(ZABs)is limited by the rapid recombination of photogenerated carriers on the photocathode.In this work,the visible-light-driven CoS_(2)/CuS@CNT-C_(3)N_(4)photocatalyst with unique petal-like layer structure was designed and developed,which can be used as air electrode for visible-light-driven ZABs.The superior performance of ZABs assembled by CoS_(2)/CuS@CNT-C_(3)N_(4)was mainly attributed to the successful construction of Schottky heterojunction between g-C_(3)N_(4)and carbon nanotubes(CNTs),which accelerates the transfer of electrons from g-C_(3)N_(4)to CoS_(2)/CuS cocatalysts,improves the carrier separation ability,and extends the carrier lifetime.Thereinto,the visible-driven ZABs assembled by CoS_(2)/CuS@CNT-C_(3)N_(4)photocatalyst has a power density of 588.90 mW cm-2 and a charge-discharge cycle of 643 h under visible light irradiation,which is the highest performance ever reported for photo-enhanced ZABs.More importantly,the charge-discharge voltage drop of ZABs was only 0.54 V under visible light irradiation,which is significantly lower than the voltage drop(0.94 V)in the dark.This study provides a new idea for designing efficient and stable visible-light-driven ZABs cathode catalysts.展开更多
The effect of preparation routes on the physical characteristics and activity of the Ag-MnOx/C composites toward the oxygen reduction reaction （ORR） in alkaline media were studied by X-ray diffraction （XRD）, X-ray...The effect of preparation routes on the physical characteristics and activity of the Ag-MnOx/C composites toward the oxygen reduction reaction （ORR） in alkaline media were studied by X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, transmission electron microscopy （TEM）, energy-dispersion spectroscopy （EDS） as well as scanning electron microscopy （SEM） and electrochemical techniques. The results show that more Ag and Mn species present on the surface of the Ag-MnOx/C composite prepared by two-step route （Ag-MnOx/C-2） compared to the one prepared by one-step route （Ag-MnOx/C-1）, which contributes to its superior activity toward the ORR. The higher electron transfer number involved in the ORR can be observed on the Ag-MnOx/C-2 composite and its specific mass kinetic current at -0.6 V （vs Hg/HgO） is 46 mA/μg, which is 23 times that on the Ag/C. The peak power density of zinc-air battery with the Ag-MnOx/C-2 air electrode reaches up to 117 mW/cm^2.展开更多
The development of highly active and stable reversible oxygen electrocatalysts is crucial for improving the efficiency of metal‐air battery devices.Herein,an efficient liquid exfoliation strategy was designed for pro...The development of highly active and stable reversible oxygen electrocatalysts is crucial for improving the efficiency of metal‐air battery devices.Herein,an efficient liquid exfoliation strategy was designed for producing silk‐like FeS2/NiS2 hybrid nanocrystals with enhanced reversible oxygen catalytic performance that displayed excellent properties for Zn‐air batteries.Because of the unique silk‐like morphology and interface nanocrystal structure,they can catalyze the oxygen evolution reaction(OER)efficiently with a low overpotential of 233 mV at j=10 mA cm?2.This is an improvement from the recently reported catalysts in 1.0 M KOH.Meanwhile,the oxygen reduction reaction(ORR)activity of the silk‐like FeS2/NiS2 hybrid nanocrystals showed an onset potential of 911 mV and a half‐wave potential of 640 mV.In addition,the reversible oxygen electrode activity of the silk‐like FeS2/NiS2 hybrid nanocrystals was calculated to be 0.823 V,based on the potential of the OER and ORR.Further,the homemade rechargeable Zn‐air batteries using FeS2/NiS2 hybrid nanocrystals as the air‐cathode displayed a high open‐circuit voltage of 1.25 V for more than 17 h and an excellent rechargeable performance for 25 h.The solid Zn‐air batteries exhibited an excellent rechargeable performance for 15 h.This study provided a new method for designing interface nanocrystals with a unique morphology for efficient multifunctional electrocatalysts in electrochemical reactions and renewable energy devices.展开更多
The sluggish kinetics of oxygen reduction reaction(ORR)hinders the commercialization of Zn‐air batteries(ZABs).Manipulating the electronic structure of electrocatalysts to optimize the adsorption energy of oxygen‐co...The sluggish kinetics of oxygen reduction reaction(ORR)hinders the commercialization of Zn‐air batteries(ZABs).Manipulating the electronic structure of electrocatalysts to optimize the adsorption energy of oxygen‐containing intermediates during the 4e–ORR offers a practical route toward improving ORR kinetics.Herein,we designed a novel ORR electrocatalyst containing Co single atoms and nanoparticles supported by carbon dots‐derived carbon nanoflowers(Co SAs/NPs CNF).Co SAs/NPs CNF possessed a very high ORR activity(E_(1/2) of the Co SAs/NPs CNF catalyst is 0.83 V(vs.RHE)),and outstanding catalytic performance and stability when used as the air‐electrode catalyst in rechargeable ZABs(152.32 mW cm^(-2),1000.58 mWh gZn^(–1),and over 1300 cycles at a current density of 5 mA cm^(-2)).The Co SAs and Co NPs cooperated to improve electron and proton transfer processes during ORR.Theoretical calculations revealed that the presence of adjacent Co NPs optimized the electronic structure of the isolated Co‐N_(4) sites,significantly lowering the energy barriers for the rate‐determining step in ORR(adsorption of*OOH)and thereby delivering outstanding ORR performance.This work reveals that the combination of supported single‐atom sites and metal nanoparticles can be highly beneficial for ORR electrocatalysis,outperforming catalysts containing only Co SAs or Co NPs.展开更多
Zn-air batteries have attracted extensive attention for their unique features including high energy density,safety,low cost and environmental friendliness.However,due to their poor chargeability and low efficiency,the...Zn-air batteries have attracted extensive attention for their unique features including high energy density,safety,low cost and environmental friendliness.However,due to their poor chargeability and low efficiency,the practical application remains a challenge.The main obstacles are the intrinsic slow reaction kinetics on air cathodes,including oxygen reduction reaction during the discharging process and oxygen evolution reaction during the recharging process.Searching for efficient bifunctional oxygen electrocatalysts is key to solve these problems.In this review,the configuration and fundamental oxygen electrochemical reactions on air cathodes are briefly introduced for Zn-air batteries first.Then,the latest bifunctional oxygen electrocatalysts are summarized in detail.Finally,the perspectives are provided for the future investigations on bifunctional oxygen electrocatalysts.展开更多
The application of electrocatalysts for the oxygen reduction reaction(ORR) is vital in a variety of energy conversion technologies. Exploring low-cost ORR catalysts with high activity and long-term stability is highly...The application of electrocatalysts for the oxygen reduction reaction(ORR) is vital in a variety of energy conversion technologies. Exploring low-cost ORR catalysts with high activity and long-term stability is highly desirable, although it still remains challenging. Herein, we report a facile and reliable route to convert ZIF-8 modified by Fe-phenanthroline into Fe-incorporated and N-doped carbon dodecahedron nanoarchitecture(Fe-NCDNA), in which carbon nanosheets are formed in situ as the building blocks with uniform Fe-N-C species decoration. Systematic electrochemical studies demonstrate that the as-synthesized Fe-NCDNA electrocatalyst possesses highly attractive catalytic features toward the ORR in terms of activity and durability in both alkaline and neutral media. The Zn-air battery with the optimal Fe-NCDNA catalyst as the cathode performs impressively, delivering a power density of 184 m W cm^–2 and a specific capacity of 801 m Ah g^–1;thus, it exhibits great competitive advantages over those of the Zn-air devices employing a Pt-based cathode electrocatalyst.展开更多
A series of transition metal nitrides(MxNy,M=Fe,Co,Ni)nanoparticle(NP)composites caged in N-doped hollow porous carbon sphere(NHPCS)were prepared by impregnation and heat treatment methods.These composites combine the...A series of transition metal nitrides(MxNy,M=Fe,Co,Ni)nanoparticle(NP)composites caged in N-doped hollow porous carbon sphere(NHPCS)were prepared by impregnation and heat treatment methods.These composites combine the high catalytic activity of nitrides and the high-efficiency mass transfer characteristics of NHPCS.The oxygen reduction reaction results indicate that Fe2N/NHPCS has the synergistic catalytic performance of higher onset potential(0.96 V),higher electron transfer number(~4)and higher limited current density(1.4 times as high as that of commercial Pt/C).In addition,this material is implemented as the air catalyst for zinc−air battery that exhibits considerable specific capacity(795.1 mA·h/g)comparable to that of Pt/C,higher durability and maximum power density(173.1 mW/cm2).展开更多
Integrating two different catalytic active sites into one composite is a useful 2-in-1 strategy for designing high-efficient bifunctional catalysts,which can easily tailor the activity of each reaction.Hence,we adopt ...Integrating two different catalytic active sites into one composite is a useful 2-in-1 strategy for designing high-efficient bifunctional catalysts,which can easily tailor the activity of each reaction.Hence,we adopt the 2-in-1 strategy to design the metal oxyhydroxide supported on N-doped porous carbons(PA-CoFe@NPC)as the oxygen bifunctional catalyst,where NPC provides the activity for oxygen reduction reaction(ORR)while the metal oxyhydroxide is responsible for oxygen evolution reaction(OER).Results demonstrate that the PA-CoFe@NPC indeed exhibits both super ORR and OER activities.Impressively,using bifunctional PA-CoFe@NPC as the oxygen electrode,the resulting Zn-air battery exhibits outstanding charge and discharge performance with the peak power density of 156.3 mW cm^(-2),and also exhibits a long-term cycle stability with continuous cyclic charge and discharge of 170 hours that is obviously better than the 20%Pt/C+IrO_(2)based one.The 2-in-1 strategy in this work can be efficiently extended to design other bi-or multi-functional electrocatalysts.展开更多
The rational design of efficient and stable carbon-based electrocatalysts for oxygen reduction and oxygen evolution reactions is crucial for improving energy density and long-term stability of rechargeable zinc-air ba...The rational design of efficient and stable carbon-based electrocatalysts for oxygen reduction and oxygen evolution reactions is crucial for improving energy density and long-term stability of rechargeable zinc-air batteries(ZABs).Herein,a general and controllable synthesis method was developed to prepare three-dimensional(3D)porous carbon composites embedded with diverse metal phosphide nanocrystallites by interfacial coordination of transition metal ions with phytic acid-doped polyaniline networks and subsequent pyrolysis.Phytic acid as the dopant of polyaniline provides favorable anchoring sites for metal ions owing to the coordination interaction.Specifically,adjusting the concentration of adsorbed cobalt ions can achieve the phase regulation of transition metal phosphides.Thus,with abundant cobalt phosphide nanoparticles and nitrogen-and phosphorus-doping sites,the obtained carbon-based electrocatalysts exhibited efficient electrocatalytic activities toward oxygen reduction and evolution reactions.Consequently,the fabricated ZABs exhibited a high energy density,high power density of 368 mW cm^(-2),and good cycling/mechanical stability,which could power water splitting for integrated device fabrication with high gas yields.展开更多
Efficient and affordable electrocatalysts for reversible oxygen reduction and oxygen evolution reactions(ORR and OER,respectively)are highly sought-after for use in rechargeable metal-air batteries.However,the constru...Efficient and affordable electrocatalysts for reversible oxygen reduction and oxygen evolution reactions(ORR and OER,respectively)are highly sought-after for use in rechargeable metal-air batteries.However,the construction of high-performance electrocatalysts that possess both largely accessible active sites and superior ORR/OER intrinsic activities is challenging.Herein,we report the design and successful preparation of a 3D hierarchically porous graphene framework with interconnected interlayer macropores and in-plane mesopores,enriched with pyridinic-nitrogen-cobalt(pyri-N-Co)active sites,namely,CoFe/3D-NLG.The pyri-N-Co bonding significantly accelerates sluggish oxygen electrocatalysis kinetics,in turn substantially improving the intrinsic ORR/OER activities per active site,while copious interlayer macropores and in-plane mesopores enable ultra-efficient mass transfer throughout the graphene architecture,thus ensuring sufficient exposure of accessible pyri-N-Co active sites to the reagents.Such a robust catalyst structure endows CoFe/3D-NLG with a remarkably enhanced reversible oxygen electrocatalysis performance,with the ORR half-wave potential identical to that of the benchmark Pt/C catalyst,and OER activity far surpassing that of the noble-metal-based RuO2 catalyst.Moreover,when employed as an air electrode for a rechargeable Zn-air battery,CoFe/3D-NLG manifests an exceedingly high open-circuit voltage(1.56 V),high peak power density(213 mW cm^(–2)),ultra-low charge/discharge voltage(0.63 V),and excellent charge/discharge cycling stability,outperforming state-of-the-art noble-metal electrocatalysts.展开更多
文摘Storing solar energy in battery systems is crucial to achieving a green and sustainable society.However,the efficient development of photo-enhanced zinc-air batteries(ZABs)is limited by the rapid recombination of photogenerated carriers on the photocathode.In this work,the visible-light-driven CoS_(2)/CuS@CNT-C_(3)N_(4)photocatalyst with unique petal-like layer structure was designed and developed,which can be used as air electrode for visible-light-driven ZABs.The superior performance of ZABs assembled by CoS_(2)/CuS@CNT-C_(3)N_(4)was mainly attributed to the successful construction of Schottky heterojunction between g-C_(3)N_(4)and carbon nanotubes(CNTs),which accelerates the transfer of electrons from g-C_(3)N_(4)to CoS_(2)/CuS cocatalysts,improves the carrier separation ability,and extends the carrier lifetime.Thereinto,the visible-driven ZABs assembled by CoS_(2)/CuS@CNT-C_(3)N_(4)photocatalyst has a power density of 588.90 mW cm-2 and a charge-discharge cycle of 643 h under visible light irradiation,which is the highest performance ever reported for photo-enhanced ZABs.More importantly,the charge-discharge voltage drop of ZABs was only 0.54 V under visible light irradiation,which is significantly lower than the voltage drop(0.94 V)in the dark.This study provides a new idea for designing efficient and stable visible-light-driven ZABs cathode catalysts.
基金Project(21406273)supported by the National Natural Science Foundation of China
文摘The effect of preparation routes on the physical characteristics and activity of the Ag-MnOx/C composites toward the oxygen reduction reaction （ORR） in alkaline media were studied by X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, transmission electron microscopy （TEM）, energy-dispersion spectroscopy （EDS） as well as scanning electron microscopy （SEM） and electrochemical techniques. The results show that more Ag and Mn species present on the surface of the Ag-MnOx/C composite prepared by two-step route （Ag-MnOx/C-2） compared to the one prepared by one-step route （Ag-MnOx/C-1）, which contributes to its superior activity toward the ORR. The higher electron transfer number involved in the ORR can be observed on the Ag-MnOx/C-2 composite and its specific mass kinetic current at -0.6 V （vs Hg/HgO） is 46 mA/μg, which is 23 times that on the Ag/C. The peak power density of zinc-air battery with the Ag-MnOx/C-2 air electrode reaches up to 117 mW/cm^2.
基金supported by the National Basic Research Program of China(21571089,21503102,51571125)the Fundamental Research Funds for the Central Universities(lzujbky-2016-k02,lzujbky-2018-k08,lzujbky-2017-it42)~~
文摘The development of highly active and stable reversible oxygen electrocatalysts is crucial for improving the efficiency of metal‐air battery devices.Herein,an efficient liquid exfoliation strategy was designed for producing silk‐like FeS2/NiS2 hybrid nanocrystals with enhanced reversible oxygen catalytic performance that displayed excellent properties for Zn‐air batteries.Because of the unique silk‐like morphology and interface nanocrystal structure,they can catalyze the oxygen evolution reaction(OER)efficiently with a low overpotential of 233 mV at j=10 mA cm?2.This is an improvement from the recently reported catalysts in 1.0 M KOH.Meanwhile,the oxygen reduction reaction(ORR)activity of the silk‐like FeS2/NiS2 hybrid nanocrystals showed an onset potential of 911 mV and a half‐wave potential of 640 mV.In addition,the reversible oxygen electrode activity of the silk‐like FeS2/NiS2 hybrid nanocrystals was calculated to be 0.823 V,based on the potential of the OER and ORR.Further,the homemade rechargeable Zn‐air batteries using FeS2/NiS2 hybrid nanocrystals as the air‐cathode displayed a high open‐circuit voltage of 1.25 V for more than 17 h and an excellent rechargeable performance for 25 h.The solid Zn‐air batteries exhibited an excellent rechargeable performance for 15 h.This study provided a new method for designing interface nanocrystals with a unique morphology for efficient multifunctional electrocatalysts in electrochemical reactions and renewable energy devices.
文摘The sluggish kinetics of oxygen reduction reaction(ORR)hinders the commercialization of Zn‐air batteries(ZABs).Manipulating the electronic structure of electrocatalysts to optimize the adsorption energy of oxygen‐containing intermediates during the 4e–ORR offers a practical route toward improving ORR kinetics.Herein,we designed a novel ORR electrocatalyst containing Co single atoms and nanoparticles supported by carbon dots‐derived carbon nanoflowers(Co SAs/NPs CNF).Co SAs/NPs CNF possessed a very high ORR activity(E_(1/2) of the Co SAs/NPs CNF catalyst is 0.83 V(vs.RHE)),and outstanding catalytic performance and stability when used as the air‐electrode catalyst in rechargeable ZABs(152.32 mW cm^(-2),1000.58 mWh gZn^(–1),and over 1300 cycles at a current density of 5 mA cm^(-2)).The Co SAs and Co NPs cooperated to improve electron and proton transfer processes during ORR.Theoretical calculations revealed that the presence of adjacent Co NPs optimized the electronic structure of the isolated Co‐N_(4) sites,significantly lowering the energy barriers for the rate‐determining step in ORR(adsorption of*OOH)and thereby delivering outstanding ORR performance.This work reveals that the combination of supported single‐atom sites and metal nanoparticles can be highly beneficial for ORR electrocatalysis,outperforming catalysts containing only Co SAs or Co NPs.
基金supported by the National Natural Science Foundation of China NSFC(51702166)Tianjin Municipal Science and Technology Bureau(17JCZDJC37100)~~
文摘Zn-air batteries have attracted extensive attention for their unique features including high energy density,safety,low cost and environmental friendliness.However,due to their poor chargeability and low efficiency,the practical application remains a challenge.The main obstacles are the intrinsic slow reaction kinetics on air cathodes,including oxygen reduction reaction during the discharging process and oxygen evolution reaction during the recharging process.Searching for efficient bifunctional oxygen electrocatalysts is key to solve these problems.In this review,the configuration and fundamental oxygen electrochemical reactions on air cathodes are briefly introduced for Zn-air batteries first.Then,the latest bifunctional oxygen electrocatalysts are summarized in detail.Finally,the perspectives are provided for the future investigations on bifunctional oxygen electrocatalysts.
文摘The application of electrocatalysts for the oxygen reduction reaction(ORR) is vital in a variety of energy conversion technologies. Exploring low-cost ORR catalysts with high activity and long-term stability is highly desirable, although it still remains challenging. Herein, we report a facile and reliable route to convert ZIF-8 modified by Fe-phenanthroline into Fe-incorporated and N-doped carbon dodecahedron nanoarchitecture(Fe-NCDNA), in which carbon nanosheets are formed in situ as the building blocks with uniform Fe-N-C species decoration. Systematic electrochemical studies demonstrate that the as-synthesized Fe-NCDNA electrocatalyst possesses highly attractive catalytic features toward the ORR in terms of activity and durability in both alkaline and neutral media. The Zn-air battery with the optimal Fe-NCDNA catalyst as the cathode performs impressively, delivering a power density of 184 m W cm^–2 and a specific capacity of 801 m Ah g^–1;thus, it exhibits great competitive advantages over those of the Zn-air devices employing a Pt-based cathode electrocatalyst.
基金the National Natural Science Foundation of China(Nos.51702137,51802128)the Natural Science Foundation of Jiangsu Province,China(No.BK20181013)+1 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutions,China(No.18KJB430013)the Foundation of State Key Laboratory of High-Efficiency Utilization of Coal and Green Chemical Engineering,China(No.2020-KF-20).
文摘A series of transition metal nitrides(MxNy,M=Fe,Co,Ni)nanoparticle(NP)composites caged in N-doped hollow porous carbon sphere(NHPCS)were prepared by impregnation and heat treatment methods.These composites combine the high catalytic activity of nitrides and the high-efficiency mass transfer characteristics of NHPCS.The oxygen reduction reaction results indicate that Fe2N/NHPCS has the synergistic catalytic performance of higher onset potential(0.96 V),higher electron transfer number(~4)and higher limited current density(1.4 times as high as that of commercial Pt/C).In addition,this material is implemented as the air catalyst for zinc−air battery that exhibits considerable specific capacity(795.1 mA·h/g)comparable to that of Pt/C,higher durability and maximum power density(173.1 mW/cm2).
文摘Integrating two different catalytic active sites into one composite is a useful 2-in-1 strategy for designing high-efficient bifunctional catalysts,which can easily tailor the activity of each reaction.Hence,we adopt the 2-in-1 strategy to design the metal oxyhydroxide supported on N-doped porous carbons(PA-CoFe@NPC)as the oxygen bifunctional catalyst,where NPC provides the activity for oxygen reduction reaction(ORR)while the metal oxyhydroxide is responsible for oxygen evolution reaction(OER).Results demonstrate that the PA-CoFe@NPC indeed exhibits both super ORR and OER activities.Impressively,using bifunctional PA-CoFe@NPC as the oxygen electrode,the resulting Zn-air battery exhibits outstanding charge and discharge performance with the peak power density of 156.3 mW cm^(-2),and also exhibits a long-term cycle stability with continuous cyclic charge and discharge of 170 hours that is obviously better than the 20%Pt/C+IrO_(2)based one.The 2-in-1 strategy in this work can be efficiently extended to design other bi-or multi-functional electrocatalysts.
文摘The rational design of efficient and stable carbon-based electrocatalysts for oxygen reduction and oxygen evolution reactions is crucial for improving energy density and long-term stability of rechargeable zinc-air batteries(ZABs).Herein,a general and controllable synthesis method was developed to prepare three-dimensional(3D)porous carbon composites embedded with diverse metal phosphide nanocrystallites by interfacial coordination of transition metal ions with phytic acid-doped polyaniline networks and subsequent pyrolysis.Phytic acid as the dopant of polyaniline provides favorable anchoring sites for metal ions owing to the coordination interaction.Specifically,adjusting the concentration of adsorbed cobalt ions can achieve the phase regulation of transition metal phosphides.Thus,with abundant cobalt phosphide nanoparticles and nitrogen-and phosphorus-doping sites,the obtained carbon-based electrocatalysts exhibited efficient electrocatalytic activities toward oxygen reduction and evolution reactions.Consequently,the fabricated ZABs exhibited a high energy density,high power density of 368 mW cm^(-2),and good cycling/mechanical stability,which could power water splitting for integrated device fabrication with high gas yields.
文摘Efficient and affordable electrocatalysts for reversible oxygen reduction and oxygen evolution reactions(ORR and OER,respectively)are highly sought-after for use in rechargeable metal-air batteries.However,the construction of high-performance electrocatalysts that possess both largely accessible active sites and superior ORR/OER intrinsic activities is challenging.Herein,we report the design and successful preparation of a 3D hierarchically porous graphene framework with interconnected interlayer macropores and in-plane mesopores,enriched with pyridinic-nitrogen-cobalt(pyri-N-Co)active sites,namely,CoFe/3D-NLG.The pyri-N-Co bonding significantly accelerates sluggish oxygen electrocatalysis kinetics,in turn substantially improving the intrinsic ORR/OER activities per active site,while copious interlayer macropores and in-plane mesopores enable ultra-efficient mass transfer throughout the graphene architecture,thus ensuring sufficient exposure of accessible pyri-N-Co active sites to the reagents.Such a robust catalyst structure endows CoFe/3D-NLG with a remarkably enhanced reversible oxygen electrocatalysis performance,with the ORR half-wave potential identical to that of the benchmark Pt/C catalyst,and OER activity far surpassing that of the noble-metal-based RuO2 catalyst.Moreover,when employed as an air electrode for a rechargeable Zn-air battery,CoFe/3D-NLG manifests an exceedingly high open-circuit voltage(1.56 V),high peak power density(213 mW cm^(–2)),ultra-low charge/discharge voltage(0.63 V),and excellent charge/discharge cycling stability,outperforming state-of-the-art noble-metal electrocatalysts.
