Zhuang Zechao, Li Yong, Huang Jiazhao, Li Zilan, Zhao Kangning, Zhao Yunlong, Xu Lin, Zhou Liang, Moskaleva Lyudmila V, Mai Liqiang
State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, International School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China.
Institute of Applied and Physical Chemistry and Center for Environmental Research and Sustainable Technology, University of Bremen, Bremen 28359, Germany.
Sci Bull (Beijing). 2019 May 15;64(9):617-624. doi: 10.1016/j.scib.2019.04.005. Epub 2019 Apr 2.
Nonmetal elements strictly govern the electrochemical performance of molybdenum compounds. Yet, the exact role played by nonmetals during electrocatalysis remains largely obscure. With intermetallic MoSi comprising silicene subunits, we present an unprecedented hydrogen evolution reaction (HER) behavior in aqueous alkaline solution. Under continuous operation, the HER activity of MoSi shows a more than one order of magnitude improvement in current density from 1.1 to 21.5 mA cm at 0.4 V overpotential. Meanwhile, this activation behavior is highly reversible, such that voltage withdrawal leads to catalyst inactivation but another operation causes reactivation. Thus, the system shows dynamics strikingly analogous to the legendary Sisyphus' labor, which drops and recovers in a stepwise manner repeatedly, but never succeeds in reaching the top of the mountain. Isomorphic WSi behaves almost the same as MoSi, whereas other metal silicides with silicyne subunits, including CrSi and TaSi, do not exhibit any anomalous behavior. A thin amorphous shell of MoSi is observed after reaction, within which the Si remains partially oxidized while the oxidation state of Mo is basically unchanged. First-principles calculations further reveal that the adsorption of hydroxide ions on silicene subunit edges and the subsequent Si vacancy formation in MoSi jointly lead to the anomalous HER kinetics of the adjacent Mo active centers. This work demonstrates that the role of nonmetal varies dramatically with the electronic and crystallographic structures of silicides and that silicene structural subunit may serve as a promoter for boosting HER in alkaline media.
非金属元素严格控制着钼化合物的电化学性能。然而，非金属在电催化过程中所起的确切作用仍 largely 不清楚。对于包含硅烯亚基的金属间化合物 MoSi，我们在碱性水溶液中展示了前所未有的析氢反应（HER）行为。在连续运行下，MoSi 的 HER 活性在 0.4 V 过电位下，电流密度从 1.1 提高到 21.5 mA cm，提高了一个多数量级。同时，这种活化行为是高度可逆的，即撤去电压会导致催化剂失活，但再次运行会导致重新活化。因此，该系统表现出与传说中的西西弗斯劳作惊人相似的动力学，它以逐步的方式反复下降和恢复，但永远无法成功到达山顶。同构的 WSi 表现与 MoSi 几乎相同，而其他具有硅炔亚基的金属硅化物，包括 CrSi 和 TaSi，则没有表现出任何异常行为。反应后观察到 MoSi 有一层薄的非晶态外壳，其中 Si 仍部分被氧化，而 Mo 的氧化态基本不变。第一性原理计算进一步揭示，氢氧根离子在硅烯亚基边缘的吸附以及随后 MoSi 中 Si 空位的形成共同导致了相邻 Mo 活性中心异常的 HER 动力学。这项工作表明，非金属的作用会随着硅化物的电子和晶体结构而显著变化，并且硅烯结构亚基可以作为在碱性介质中促进 HER 的促进剂。
