钴钒水滑石纳米片用于电催化尿素氧化

Cobalt-Vanadium Layered Double Hydroxides Nanosheets as High-Performance Electrocatalysts for Urea Oxidation Reaction

电解水是一种常用的制氢方法,但高能耗的阳极析氧反应(OER)阻碍了其应用。尿素氧化反应(UOR)具有较低的热力学电势,是最有前景的OER替代反应之一。过渡金属基水滑石具有独特的层状结构和层间阴离子可交换等优点,被认为是性能优异的UOR催化剂,然而目前大多数研究主要聚焦于后过渡金属元素。该研究通过一步法制备了具有前/后过渡金属的CoV-LDHs纳米片。与相同方法制备的Co(OH)_(2)相比,CoV-LDHs纳米片具有以下优点:1)纳米片结构有利于暴露更多的活性位点。2)V的引入增强了CoV-LDHs的亲水性,提高了其本征电催化动力学。3)Co(3d^(7)4s^(2))和V(3d^(3)4s^(2))之间的d-电子补偿效应有利于促进尿素的吸附。因此,CoV-LDHs仅需要1.52 V(vs.RHE)就可以达到10 mA·cm^(−2)的电流密度,比Co(OH)_(2)低了70 mV,同时CoV-LDHs较低的塔菲尔斜率表明了其较快的反应动力学。此外,CoV-LDHs在连续反应10 h后,驱动电位几乎没有增加,表明其具有良好的稳定性。该研究结果不仅证明了前/后过渡金属之间的d-电子补偿效应可以提高UOR催化性能,还为设计高效的UOR催化剂提供了可行的途径。

Hydrogen is considered as a desirable clean energy source for supporting human life in the future.Electrochemical water splitting is a promising method for generating carbon-free hydrogen.However,the relatively high overpotential of anodic oxygen evolution reaction(OER)is the main obstacle hindering the widespread popularity of water electrocatalysis technology.Recently,urea oxidation reaction(UOR)has gained significant attention as a potential alternative to OER for hydrogen production since the equilibrium potential of UOR is 0.86 V lower than that of OER.Transition metal-based layered double hydroxides(TM-LDHs)have been explored as promising UOR electrocatalysts,with the advantages of diversified metal species,stable twodimensional layered structure and exchangeability of interlayer anions.To date,most studies have focused on TM-LDHs of late transition metals(e.g.,Ni,Co,and Fe).In this work,by combining early and late transition metals,CoV-LDHs nanosheets were fabricated via a simple one-step coprecipitation method as high-performance UOR electrocatalysts.Additionally,cobalt hydroxide(Co(OH)_(2)),with a similar lamellar structure,was synthesized via the same method.When compared with Co(OH)_(2),CoV-LDHs nanosheets exhibited better UOR performance owing to the following advantages:1)The nanosheet structure of the as-fabricated CoV-LDHs electrocatalyst exposed a high number of active sites for the electrocatalytic conversion of urea.2)The introduction of V enhanced the wettability of the CoV-LDHs electrocatalyst;thus,increasing its intrinsic electrocatalytic kinetics.3)The d-electron compensation effect between Co(3d^(7)4s^(2))and V(3d^(3)4s^(2))was conducive to promoting the adsorption of urea.Therefore,the CoV-LDHs electrocatalyst exhibited a low electrochemical potential(1.52 V vs.the reversible hydrogen electrode,RHE)to achieve a current density of 10 mA·cm^(−2) in 1 mol·L^(−1) of potassium hydroxide containing 0.33 mol·L^(−1) urea,which was 70 mV less than that of Co(OH)_(2).The Tafel slope value of the CoV-LDHs electrocatalyst(99.9 mV·dec^(−1))was lower than that of Co(OH)_(2)(115.9 mV·dec^(−1)),indicating faster UOR kinetics over the CoV-LDHs electrocatalyst.Furthermore,the CoV-LDHs electrocatalyst displayed high stability,with a negligible potential increase after a 10-h chronopotentiometry test by maintaining the current density of 10 mA·cm^(−2).In conclusion,the present work not only shows that the d-electron compensation effect between early and late transition metals could adjust the local electronic structure of TM-LDHs to improve the UOR efficiency,but also provides a feasible route to design dedicated nanostructured TM-LDHs as high-performance UOR electrocatalysts.