碱性阴离子膜燃料电池和电解水制氢技术对氢能的高效循环利用非常关键.然而,碱性条件下析氢反应(HER)和氢氧化反应(HOR)动力学缓慢,大大降低了燃料电池和电解池的能量转换效率.因此,开发综合性能优异的电催化剂以提高碱性环境下HER和HO...碱性阴离子膜燃料电池和电解水制氢技术对氢能的高效循环利用非常关键.然而,碱性条件下析氢反应(HER)和氢氧化反应(HOR)动力学缓慢,大大降低了燃料电池和电解池的能量转换效率.因此,开发综合性能优异的电催化剂以提高碱性环境下HER和HOR动力学至关重要.传统电催化剂的一个典型设计思路是将活性材料负载于具有高导电性和大比表面积的碳载体上.一般来说,碳载体能够促进活性材料的均匀分散并显著增加其催化活性位点的暴露,但是碳载体本身往往很难参与电催化反应,导致复合催化剂活性位点单一,不利于高效催化涉及较多中间体的复杂反应(碱性条件下的HOR和HER).另一方面,当前电催化剂研究通常局限于调控活性材料和载体的界面结构或者专注于调控活性材料本征结构,对催化剂载体进行调控并作为助催化剂的研究尚不多见.本文采用过渡金属单原子对碳载体进行功能化及电子结构调控,并研究此类碳载体在碱性HER和HOR反应中的助催化作用.合成了一系列金属单原子修饰的碳载体M-N-C(过渡金属包括Mn,Fe,Co,Ni,Cu,Mo,Ag),并系统研究了M-N-C在Pt电催化HOR和HER中的作用.结果表明,过渡金属单原子修饰的碳载体的催化促进作用与过渡金属的电负性以及3d轨道电子填充度密切相关.一方面,不同过渡金属M与氧的亲和力不同,并可以通过界面M–O–Pt键调节Pt的电子结构.过渡金属电负性越小,Pt表面的电子密度则越大,有助于加速Had在Pt表面的结合/解离步骤,因此提升了HOR和HER反应速率.另一方面,过渡金属的3d轨道未填充程度越高,则越有利于增强其与氧2p轨道的耦合作用,所形成的M-N4结构对于水分子和OH_(ad)的吸附也大大增强,最终通过促进Volmer步骤加快氢的电催化反应速率.结果显示,除Cu和Ag单原子修饰的碳载体之外,其它几种过渡金属功能化的碳载体均能够通过促进Volmer反应步骤以加快碱性条件下Pt的HOR和HER电催化反应速率,其中效果最为显著的是锰单原子修饰的碳载体.Mn-N-C/Pt(1.48 mA cm_(Pt)^(–2))的质量比交换电流密度比商业化20%Pt/C(0.26 mA cm_(Pt)^(–2))提高了约4.7倍.综上所述,本工作证明了开发多功能碳载体用于异相催化反应的重要性,并且为未来开发高效电催化剂提供了新的思路.展开更多
It is a considerably promising strategy to produce fuels and high-value chemicals through an electrochemical conversion process in the green and sustainable energy systems.Catalysts for electrocatalytic reactions,incl...It is a considerably promising strategy to produce fuels and high-value chemicals through an electrochemical conversion process in the green and sustainable energy systems.Catalysts for electrocatalytic reactions,including hydrogen evolution reaction(HER),oxygen evolution reaction(OER),oxygen reduction reaction(ORR),nitrogen reduction reaction(NRR),carbon dioxide reduction reaction(CO_(2)RR),play a significant role in the advanced energy conversion technologies,such as water splitting devices,fuel cells,and rechargeable metal-air batteries.Developing low-cost and highly efficient electrocatalysts is closely related to establishing the composition-structure-activity relationships and fundamental understanding of catalytic mechanisms.Density functional theory(DFT)is emerging as an important computational tool that can provide insights into the relationship between the electrochemical performances and physical/chemical properties of catalysts.This article presents a review on the progress of the DFT,and the computational simulations,within the framework of DFT,for the electrocatalytic processes,as well as the computational designs and virtual screenings of new electrocatalysts.Some useful descriptors and analysis tools for evaluating the electrocatalytic performances are highlighted,including formation energies,d-band model,scaling relation,egorbital occupation,and free energies of adsorption.Furthermore,the remaining questions and perspectives for the development of DFT for electrocatalysis are also proposed.展开更多
Nitrogen(N_(2))fixation at ambient condition by electrochemical N_(2)reduction reaction(NRR)is energy-efficient and eco-friendly as compared to the traditional Harber–Bosch process,but it is extremely challenging.Dev...Nitrogen(N_(2))fixation at ambient condition by electrochemical N_(2)reduction reaction(NRR)is energy-efficient and eco-friendly as compared to the traditional Harber–Bosch process,but it is extremely challenging.Development and design of high-performance NRR electrocatalysts are indispensable to achieve the goal.In this work,a strongly coupled hybrid of nano-Fe3O4 with reduced graphene oxide(rGO)is synthesized via an in situ redox hydrothermal approach,and the synthesized Fe_(3)O_(4)@r GO hybrid has excellent activity,selectivity,and stability as an NRR catalyst.The NH_(3) yield rate of 28.01μg h^(-1)mg^(-1)at-0.3 V and the Faradaic efficiency(FE)of 19.12%at-0.1 V are obtained in 0.1 M Na_(2)SO_(4) solutions at ambient conditions.The superior NRR performance is attributed to the chemical coupling effect between r GO and nano-Fe_(3)O_(4) particles,which leads to the enhancement of the binding affinity to N_(2) molecules,improvement of the conductivity,and lowering the free energy of reaction for the limiting reaction step.This work provides a facile route in fabricating hybrid NRR catalysts with superior performance and shed lights on the reaction mechanism with theoretical mechanistic calculations.展开更多
Metal silicate hydroxides have been recognized as efficient oxygen evolution reaction(OER)electrocatalysts,yet tailoring of their intrinsic activity remains confused.Herein,Fe had been incorporated into cobalt silicat...Metal silicate hydroxides have been recognized as efficient oxygen evolution reaction(OER)electrocatalysts,yet tailoring of their intrinsic activity remains confused.Herein,Fe had been incorporated into cobalt silicate hydroxide nanosheets and the resulted material achieves a competitive OER catalytic activity.It is found that the doping state obviously affects the electrical transport property.Specifically,highly dispersed Fe atoms(low-concentration Fe doping)trigger slight electron transfer to Co atoms while serried Fe(highconcentration Fe doping)attract vast electrons.By introducing 6 at.%Fe doping,partial relatively inert Co sites are activated by atomically dispersed Fe,bearing an optimal metal 3d electronic occupation and adsorption capacity to oxygen intermediate.The introduced Co-O-Fe unit trigger the p-donation effect and decrease the number of electrons in p*-antibonding orbitals,which enhance the Fe-O covalency and the structural stability.As a result,the sample delivers a low overpotential of 293 mV to achieve a current density of 10 mA cm^(-2).This work clarifies the superiority of atomically dispersed doping state,which is of fundamental interest to the design of doped catalyst.展开更多
Although the performance of the self-standing electrode has been enhanced for aqueous zinc-ion batteries(AZIBs),it is necessary to explore and analyse the deep modification mechanism(especially interface effects).Here...Although the performance of the self-standing electrode has been enhanced for aqueous zinc-ion batteries(AZIBs),it is necessary to explore and analyse the deep modification mechanism(especially interface effects).Herein,density functional theory(DFT)calculations are applied to investigate the high-performance cathode based on the VO_(2)/carbon cloth composites with heterostructures interface(H-VO_(2)@CC).The adsorption energy comparisons and electron structure analyses verify that HVO_(2)@CC has extra activated sites at the interface,enhanced electrical conductivity,and structural stability for achieving highperformance AZIBs due to the presence of built-in electric field at the interfaces.Accordingly,the designed self-standing HVO_(2)@CC cathode delivers higher rate capacity,longer-life cyclability,and faster electronic/ion transmission kinetics benefiting from the synergistic effects.The risks of active material shedding and dissolution during the dis/charge process of two cathodes were evaluated via ex-situ ultraviolet–visible(UV–vis)spectrum and inductively coupled plasma-atomic emission spectroscopy(ICP-AES)technique.Finally,this investigation also explores the charge storage mechanism of H-VO_(2)@CC through various exsitu and in-situ characterization techniques.This finding can shed light on the significant potential of heterostructures interface engineering in practical applications and provide a valuable direction for the development of cathode materials for AZIBs and other metal-ion batteries.展开更多
Matrix-vector multiplication is the key operation for many computationally intensive algorithms. The emerging metal oxide resistive switching random access memory (RRAM) device and RRAM crossbar array have demonstra...Matrix-vector multiplication is the key operation for many computationally intensive algorithms. The emerging metal oxide resistive switching random access memory (RRAM) device and RRAM crossbar array have demonstrated a promising hardware realization of the analog matrix-vector multiplication with ultra-high energy efficiency. In this paper, we analyze the impact of both device level and circuit level non-ideal factors, including the nonlinear current-voltage relationship of RRAM devices, the variation of device fabrication and write operation, and the interconnect resistance as well as other crossbar array parameters. On top of that, we propose a technological exploration flow for device parameter configuration to overcome the impact of non-ideal factors and achieve a better trade-off among performance, energy, and reliability for each specific application. Our simulation results of a support vector machine (SVM) and Mixed National Institute of Standards and Technology (MNIST) pattern recognition dataset show that RRAM crossbar array based SVM is robust to input signal fluctuation but sensitive to tunneling gap deviation. A further resistance resolution test presents that a 6-bit RRAM device is able to realize a recognition accuracy around 90%, indicating the physical feasibility of RRAM crossbar array based SVM. In addition, the proposed technological exploration flow is able to achieve 10.98% improvement of recognition accuracy on the MNIST dataset and 26.4% energy savings compared with previous work. Experimental results also show that more than 84.4% power saving can be achieved at the cost of little accuracy reduction.展开更多
Molybdenum disulfide (MoS2) is an earth-abundant and low-cost hydrogen evolving electrocatalyst with the potential to replace traditional noble metal catalysts. The catalytic activity can be significantly enhanced a...Molybdenum disulfide (MoS2) is an earth-abundant and low-cost hydrogen evolving electrocatalyst with the potential to replace traditional noble metal catalysts. The catalytic activity can be significantly enhanced after modification due to higher conductivity and enriched active sites. However, the underlying mechanism of the influence of the resistance of electrode material and contact resistance on the hydrogen evolution reaction (HER) process is unclear. Herein, we present a systematic study to understand the relationship between HER performance and electrode conductivity, which is bi-tuned through the electric field and photoelectrical effect. It was found that the onset overpotential consistently decreased with the increase of electrode conductivity. In addition, the reduction of the contact resistance resulted in a quicker electrochemical reaction process than enhancing the conductivity of the MoS2 nanosheet. An onset overpotential of 89 mV was achieved under 60 mW/cm^2 sunlight illumination (0.6 sun) and a simultaneous gate voltage of 3 V. These physical strategies can also be applied to other catalysts, and offer new directions to improve HER catalytic performance of semiconductor materials.展开更多
文摘碱性阴离子膜燃料电池和电解水制氢技术对氢能的高效循环利用非常关键.然而,碱性条件下析氢反应(HER)和氢氧化反应(HOR)动力学缓慢,大大降低了燃料电池和电解池的能量转换效率.因此,开发综合性能优异的电催化剂以提高碱性环境下HER和HOR动力学至关重要.传统电催化剂的一个典型设计思路是将活性材料负载于具有高导电性和大比表面积的碳载体上.一般来说,碳载体能够促进活性材料的均匀分散并显著增加其催化活性位点的暴露,但是碳载体本身往往很难参与电催化反应,导致复合催化剂活性位点单一,不利于高效催化涉及较多中间体的复杂反应(碱性条件下的HOR和HER).另一方面,当前电催化剂研究通常局限于调控活性材料和载体的界面结构或者专注于调控活性材料本征结构,对催化剂载体进行调控并作为助催化剂的研究尚不多见.本文采用过渡金属单原子对碳载体进行功能化及电子结构调控,并研究此类碳载体在碱性HER和HOR反应中的助催化作用.合成了一系列金属单原子修饰的碳载体M-N-C(过渡金属包括Mn,Fe,Co,Ni,Cu,Mo,Ag),并系统研究了M-N-C在Pt电催化HOR和HER中的作用.结果表明,过渡金属单原子修饰的碳载体的催化促进作用与过渡金属的电负性以及3d轨道电子填充度密切相关.一方面,不同过渡金属M与氧的亲和力不同,并可以通过界面M–O–Pt键调节Pt的电子结构.过渡金属电负性越小,Pt表面的电子密度则越大,有助于加速Had在Pt表面的结合/解离步骤,因此提升了HOR和HER反应速率.另一方面,过渡金属的3d轨道未填充程度越高,则越有利于增强其与氧2p轨道的耦合作用,所形成的M-N4结构对于水分子和OH_(ad)的吸附也大大增强,最终通过促进Volmer步骤加快氢的电催化反应速率.结果显示,除Cu和Ag单原子修饰的碳载体之外,其它几种过渡金属功能化的碳载体均能够通过促进Volmer反应步骤以加快碱性条件下Pt的HOR和HER电催化反应速率,其中效果最为显著的是锰单原子修饰的碳载体.Mn-N-C/Pt(1.48 mA cm_(Pt)^(–2))的质量比交换电流密度比商业化20%Pt/C(0.26 mA cm_(Pt)^(–2))提高了约4.7倍.综上所述,本工作证明了开发多功能碳载体用于异相催化反应的重要性,并且为未来开发高效电催化剂提供了新的思路.
基金Foshan Xianhu Laboratory of the Advanced Energy Science and Technology Guangdong Laboratory(XHT2020-003)the Fundamental Research Funds for the Central Universities(WUT:2020Ⅲ029,2020IVA100)。
文摘It is a considerably promising strategy to produce fuels and high-value chemicals through an electrochemical conversion process in the green and sustainable energy systems.Catalysts for electrocatalytic reactions,including hydrogen evolution reaction(HER),oxygen evolution reaction(OER),oxygen reduction reaction(ORR),nitrogen reduction reaction(NRR),carbon dioxide reduction reaction(CO_(2)RR),play a significant role in the advanced energy conversion technologies,such as water splitting devices,fuel cells,and rechargeable metal-air batteries.Developing low-cost and highly efficient electrocatalysts is closely related to establishing the composition-structure-activity relationships and fundamental understanding of catalytic mechanisms.Density functional theory(DFT)is emerging as an important computational tool that can provide insights into the relationship between the electrochemical performances and physical/chemical properties of catalysts.This article presents a review on the progress of the DFT,and the computational simulations,within the framework of DFT,for the electrocatalytic processes,as well as the computational designs and virtual screenings of new electrocatalysts.Some useful descriptors and analysis tools for evaluating the electrocatalytic performances are highlighted,including formation energies,d-band model,scaling relation,egorbital occupation,and free energies of adsorption.Furthermore,the remaining questions and perspectives for the development of DFT for electrocatalysis are also proposed.
基金Sichuan Science and Technology Program(2018GZ0459)Foshan Xianhu Laboratory of the Advanced Energy Science and Technology Guangdong Laboratory(XHT2020-003)the Fundamental Research Funds for the Central Universities(WUT:2020Ⅲ029)
文摘Nitrogen(N_(2))fixation at ambient condition by electrochemical N_(2)reduction reaction(NRR)is energy-efficient and eco-friendly as compared to the traditional Harber–Bosch process,but it is extremely challenging.Development and design of high-performance NRR electrocatalysts are indispensable to achieve the goal.In this work,a strongly coupled hybrid of nano-Fe3O4 with reduced graphene oxide(rGO)is synthesized via an in situ redox hydrothermal approach,and the synthesized Fe_(3)O_(4)@r GO hybrid has excellent activity,selectivity,and stability as an NRR catalyst.The NH_(3) yield rate of 28.01μg h^(-1)mg^(-1)at-0.3 V and the Faradaic efficiency(FE)of 19.12%at-0.1 V are obtained in 0.1 M Na_(2)SO_(4) solutions at ambient conditions.The superior NRR performance is attributed to the chemical coupling effect between r GO and nano-Fe_(3)O_(4) particles,which leads to the enhancement of the binding affinity to N_(2) molecules,improvement of the conductivity,and lowering the free energy of reaction for the limiting reaction step.This work provides a facile route in fabricating hybrid NRR catalysts with superior performance and shed lights on the reaction mechanism with theoretical mechanistic calculations.
基金supported by the National Key Research and Development Program of China(2020YFA0715004)National Natural Science Foundation of China(51832004)+1 种基金Foshan Xianhu Laboratory of the Advanced Energy Science and Technology Guangdong Laboratory(XHT2020-003)the Fundamental Research Funds for the Central Universities(195101005,2020-CL-A1-28,2020Ⅲ004GX).
文摘Metal silicate hydroxides have been recognized as efficient oxygen evolution reaction(OER)electrocatalysts,yet tailoring of their intrinsic activity remains confused.Herein,Fe had been incorporated into cobalt silicate hydroxide nanosheets and the resulted material achieves a competitive OER catalytic activity.It is found that the doping state obviously affects the electrical transport property.Specifically,highly dispersed Fe atoms(low-concentration Fe doping)trigger slight electron transfer to Co atoms while serried Fe(highconcentration Fe doping)attract vast electrons.By introducing 6 at.%Fe doping,partial relatively inert Co sites are activated by atomically dispersed Fe,bearing an optimal metal 3d electronic occupation and adsorption capacity to oxygen intermediate.The introduced Co-O-Fe unit trigger the p-donation effect and decrease the number of electrons in p*-antibonding orbitals,which enhance the Fe-O covalency and the structural stability.As a result,the sample delivers a low overpotential of 293 mV to achieve a current density of 10 mA cm^(-2).This work clarifies the superiority of atomically dispersed doping state,which is of fundamental interest to the design of doped catalyst.
基金financially supported by Shenzhen Fundamental Research Program(JCYJ20190809114409397)the Fundamental Research Funds for the Central Universities(WUT:2020Ⅲ029 and 2020IVA100)。
基金This work was financially supported by the Innovation and Entrepreneurship Training Program for College Students(No.S202110500041)the National Natural Science Foundation of China(No.51771071).
文摘Although the performance of the self-standing electrode has been enhanced for aqueous zinc-ion batteries(AZIBs),it is necessary to explore and analyse the deep modification mechanism(especially interface effects).Herein,density functional theory(DFT)calculations are applied to investigate the high-performance cathode based on the VO_(2)/carbon cloth composites with heterostructures interface(H-VO_(2)@CC).The adsorption energy comparisons and electron structure analyses verify that HVO_(2)@CC has extra activated sites at the interface,enhanced electrical conductivity,and structural stability for achieving highperformance AZIBs due to the presence of built-in electric field at the interfaces.Accordingly,the designed self-standing HVO_(2)@CC cathode delivers higher rate capacity,longer-life cyclability,and faster electronic/ion transmission kinetics benefiting from the synergistic effects.The risks of active material shedding and dissolution during the dis/charge process of two cathodes were evaluated via ex-situ ultraviolet–visible(UV–vis)spectrum and inductively coupled plasma-atomic emission spectroscopy(ICP-AES)technique.Finally,this investigation also explores the charge storage mechanism of H-VO_(2)@CC through various exsitu and in-situ characterization techniques.This finding can shed light on the significant potential of heterostructures interface engineering in practical applications and provide a valuable direction for the development of cathode materials for AZIBs and other metal-ion batteries.
基金This work was supported by the National Basic Research 973 Program of China under Grant No. 2013CB329000, the National Natural Science Foundation of China under Grant Nos. 61373026, 61261160501, the Brain Inspired Computing Research of Tsinghua University under Grant No. 20141080934, Tsinghua University Initiative Scientific Research Program, and the Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions.
文摘Matrix-vector multiplication is the key operation for many computationally intensive algorithms. The emerging metal oxide resistive switching random access memory (RRAM) device and RRAM crossbar array have demonstrated a promising hardware realization of the analog matrix-vector multiplication with ultra-high energy efficiency. In this paper, we analyze the impact of both device level and circuit level non-ideal factors, including the nonlinear current-voltage relationship of RRAM devices, the variation of device fabrication and write operation, and the interconnect resistance as well as other crossbar array parameters. On top of that, we propose a technological exploration flow for device parameter configuration to overcome the impact of non-ideal factors and achieve a better trade-off among performance, energy, and reliability for each specific application. Our simulation results of a support vector machine (SVM) and Mixed National Institute of Standards and Technology (MNIST) pattern recognition dataset show that RRAM crossbar array based SVM is robust to input signal fluctuation but sensitive to tunneling gap deviation. A further resistance resolution test presents that a 6-bit RRAM device is able to realize a recognition accuracy around 90%, indicating the physical feasibility of RRAM crossbar array based SVM. In addition, the proposed technological exploration flow is able to achieve 10.98% improvement of recognition accuracy on the MNIST dataset and 26.4% energy savings compared with previous work. Experimental results also show that more than 84.4% power saving can be achieved at the cost of little accuracy reduction.
文摘Molybdenum disulfide (MoS2) is an earth-abundant and low-cost hydrogen evolving electrocatalyst with the potential to replace traditional noble metal catalysts. The catalytic activity can be significantly enhanced after modification due to higher conductivity and enriched active sites. However, the underlying mechanism of the influence of the resistance of electrode material and contact resistance on the hydrogen evolution reaction (HER) process is unclear. Herein, we present a systematic study to understand the relationship between HER performance and electrode conductivity, which is bi-tuned through the electric field and photoelectrical effect. It was found that the onset overpotential consistently decreased with the increase of electrode conductivity. In addition, the reduction of the contact resistance resulted in a quicker electrochemical reaction process than enhancing the conductivity of the MoS2 nanosheet. An onset overpotential of 89 mV was achieved under 60 mW/cm^2 sunlight illumination (0.6 sun) and a simultaneous gate voltage of 3 V. These physical strategies can also be applied to other catalysts, and offer new directions to improve HER catalytic performance of semiconductor materials.