Zhang Yongxia, Qiu Yunfeng, Wang Yanping, Li Bing, Zhang Yuanyuan, Ma Zhuo, Liu Shaoqin
School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150080, P. R. China.
Key Laboratory of Micro-Systems and Micro-Structures Manufacturing, Ministry of Education, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150080, P. R. China.
ACS Appl Mater Interfaces. 2021 Jan 27;13(3):3937-3948. doi: 10.1021/acsami.0c19117. Epub 2021 Jan 13.
Electrochemical water splitting into hydrogen is a promising strategy for hydrogen production powered by solar energy. However, the cell voltage of an electrolyzer is still too high for practical application, which is mainly limited by the sluggish oxygen evolution reaction process. To this end, hybrid water electrolyzers have drawn tremendous attention. Herein, coaxial Ni/NiS@N-doped nanofibers are directly grown on nickel foam (NF), which is highly active for hydrogen evolution reaction. Meanwhile, the NiS@N-doped nanofibers on NF prepared in an Ar atmosphere display superior urea oxidation reaction performance to previously reported catalysts. The cell voltage is about 1.50 V in urea electrolysis to deliver a current density of 20 mA cm, lower than that of a traditional water electrolyzer (1.82 V). The current density is around 77% relative to its initial value of 20 mA cm after 20 h, superior to Pt/C|Ir/C-based urea electrolysis (14%). It is found that the synergistic effect between metallic Ni and NiS, as well as the interfacial effect between metal centers and N-doped carbon, favors the initial dissociation of HO and the adsorption/desorption of H* with thermal neutral Gibbs free energy. Meanwhile, the in-situ generated NiOOH on the outer surface of NiS possessed lower electrochemical activation energy for urea decomposition. Meanwhile, the abundant oxygen vacancies in electrodes could expose more active sites for the adsorption of intermediates, including H* and OOH*. It is also found that the hierarchical nanostructure of densely packed nanowires provides ideal electronic and ionic transport paths for fast electrocatalytic kinetics. The present work indicated that the modulation of compositions and hierarchical nanostructure is effective to prepare efficient catalysts for H production urea electrolysis.
电化学水分解制氢是一种利用太阳能制氢的有前景的策略。然而，对于实际应用而言，电解槽的电池电压仍然过高，这主要受限于缓慢的析氧反应过程。为此，混合水电解槽引起了极大关注。在此，同轴Ni/NiS@N掺杂纳米纤维直接生长在泡沫镍（NF）上，其对析氢反应具有高活性。同时，在氩气气氛中制备的NF上的NiS@N掺杂纳米纤维展现出优于先前报道催化剂的尿素氧化反应性能。在尿素电解中，电池电压约为1.50 V时可提供20 mA cm的电流密度，低于传统水电解槽的电压（1.82 V）。在20小时后，电流密度相对于其初始值20 mA cm约为77%，优于基于Pt/C|Ir/C的尿素电解（14%）。研究发现，金属Ni和NiS之间的协同效应以及金属中心与N掺杂碳之间的界面效应有利于HO的初始解离以及具有热中性吉布斯自由能的H的吸附/解吸。同时，在NiS外表面原位生成的NiOOH对尿素分解具有较低的电化学活化能。此外，电极中丰富的氧空位可暴露出更多用于吸附中间体（包括H和OOH*）的活性位点。还发现紧密堆积纳米线的分级纳米结构为快速电催化动力学提供了理想的电子和离子传输路径。目前的工作表明，组成和分级纳米结构的调控对于制备用于尿素电解制氢的高效催化剂是有效的。
