Liu Xiangye, Li Baichang, Li Xufan, Harutyunyan Avetik R, Hone James, Esposito Daniel V
Beijing National Laboratory for Molecular Sciences and State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , P.R. China.
Honda Research Institute USA Inc. , 70 Rio Robles , San Jose , California 95134 , United States.
Nano Lett. 2019 Nov 13;19(11):8118-8124. doi: 10.1021/acs.nanolett.9b03337. Epub 2019 Oct 7.
According to density functional theory, monolayer (ML) MoS is predicted to possess electrocatalytic activity for the hydrogen evolution reaction (HER) that approaches that of platinum. However, its observed HER activity is much lower, which is widely believed to result from a large Schottky barrier between ML MoS and its electrical contact. In order to better understand the role of contact resistance in limiting the performance of ML MoS HER electrocatalysts, this study has employed well-defined test platforms that allow for the simultaneous measurement of contact resistance and electrocatalytic activity toward the HER during electrochemical testing. At open circuit potential, these measurements reveal that a 0.5 M HSO electrolyte can act as a strong p-dopant that depletes free electrons in MoS and leads to extremely high contact resistance, even if the contact resistance of the as-made device in air is originally very low. However, under applied negative potentials this doping is mitigated by a strong electrolyte-mediated gating effect which can reduce the contact and sheet resistances of properly configured ML MoS electrocatalysts by more than 5 orders of magnitude. At potentials relevant to HER, the contact resistance becomes negligible and the performance of MoS electrodes is limited by HER kinetics. These findings have important implications for the design of low-dimensional semiconducting electrocatalysts and photocatalysts.
根据密度泛函理论，预测单层（ML）MoS对析氢反应（HER）具有接近铂的电催化活性。然而，其观察到的HER活性要低得多，人们普遍认为这是由于ML MoS与其电接触之间存在较大的肖特基势垒所致。为了更好地理解接触电阻在限制ML MoS HER电催化剂性能方面的作用，本研究采用了定义明确的测试平台，该平台能够在电化学测试过程中同时测量接触电阻和对HER的电催化活性。在开路电位下，这些测量结果表明，0.5 M的HSO电解质可以作为一种强p型掺杂剂，耗尽MoS中的自由电子，即使在空气中制成的器件的接触电阻原本非常低，也会导致极高的接触电阻。然而，在施加负电位时，这种掺杂会被强电解质介导的门控效应所缓解，这种效应可以将配置适当的ML MoS电催化剂的接触电阻和薄层电阻降低超过5个数量级。在与HER相关的电位下，接触电阻变得可以忽略不计，MoS电极的性能受HER动力学限制。这些发现对低维半导体电催化剂和光催化剂的设计具有重要意义。
