物理化学学报 >> 2023, Vol. 39 >> Issue (4): 2301023.doi: 10.3866/PKU.WHXB202301023

所属专题： 庆祝谢有畅教授九十华诞专刊

论文 上一篇    

NiMo(O)物相结构与电解水析氢反应活性的关联

王奥琦1,2, 陈军2,3, 张鹏飞2,3, 唐珊2,3, 冯兆池2, 姚婷婷2,3,*(), 李灿1,2,3,*()   

  1. 1 中国科学技术大学化学物理系, 合肥 230026
    2 中国科学院大连化学物理研究所催化基础国家重点实验室, 大连 116023
    3 中国科学院大学, 北京 100049
  • 收稿日期:2023-01-14 录用日期:2023-02-07 发布日期:2023-02-20
  • 通讯作者: 姚婷婷,李灿 E-mail:ttyao@dicp.ac.cn;canli@dicp.ac.cn
  • 基金资助:
    人工光合成基础科学中心(FReCAP);国家重点研发计划(2021YFB4000300);国家自然科学基金(22088102);基金委联合基金项目(U20B6002);辽宁省重大专项(2022JH1/10400020)

Relation between NiMo(O) Phase Structures and Hydrogen Evolution Activities of Water Electrolysis

Aoqi Wang1,2, Jun Chen2,3, Pengfei Zhang2,3, Shan Tang2,3, Zhaochi Feng2, Tingting Yao2,3,*(), Can Li1,2,3,*()   

  1. 1 Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
    2 State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
    3 University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2023-01-14 Accepted:2023-02-07 Published:2023-02-20
  • Contact: Tingting Yao, Can Li E-mail:ttyao@dicp.ac.cn;canli@dicp.ac.cn
  • Supported by:
    the Fundamental Research Center of Artificial Photosynthesis, China(FReCAP);financially supported by the National Key R & D Program of China(2021YFB4000300);National Natural Science Foundation of China(22088102);Jointly Funded Project of NSFC(U20B6002);the Major Program of Liaoning Province, China(2022JH1/10400020)

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摘要：

在电催化析氢反应中，NiMo(O)催化剂在高电流密度下通常表现为极低的过电位。然而，该优异电催化性能的真正起源尚不明确。一个新的角度，即研究钼镍催化剂结构/性能演变的规律，能够帮助深入理解镍钼催化剂具有高活性的本质原因。基于此，本文详细阐述了含有结晶水的钼酸镍的脱水和氧化过程，在随后的还原处理中，该演变过程也被证实对于衍生不同的催化剂相结构具有重要作用。文中通过热重-差热分析以及程序升温氢气还原的方法探究电催化剂的特征相结构演变过程。同时，借助X射线衍射仪、拉曼光谱和高分辨透射电子显微镜分析确认催化剂物相。原位电化学X射线衍射分析提供了电催化剂在反应过程中的晶相结构。本文合成了具有不同主体相结构的钼镍催化剂：MoNi4，β-NiMoO4和α-NiMoO4，它们的析氢反应活性具有显著差异。其中，β-NiMoO4作为主体相结构的NiMoO4-400air-H2催化剂在碱性水还原反应中显现出最差的析氢性能；与之相比，α-NiMoO4作为主体相结构的NiMoO4-500air-H2催化剂的活性有所提升。而从NiMoO4∙(n−x)H2O演变得到的以MoNi4为主体结构的NiMoO4-300air-H2催化剂具有最优异的电催化析氢反应活性。此外，通过电化学表面积归一化的活性与几何面积归一化的活性展现出相同的趋势。本文还通过密度泛函理论计算得到不同相结构的催化剂对于水还原反应中间物种(H2O、OH和H)的吸附强度以及水解离能力。该研究发现不同的物相所导致的催化剂结构差异能够引起其对析氢反应中间物种的吸附能力的差异，进而具有不同的水解离能力，最终导致不同的析氢活性。在β-NiMoO4上，其最差的析氢性能可归因于对三种中间物均最弱的吸附能力，阻碍了水解离过程。而对中间物种吸附能力提升，更有利于α-NiMoO4表面的水还原动力学，从而改善其析氢反应活性。相比之下，表现为相对最强中间物种吸附能力的MoNi4具有最优异的催化性能。实验中β-NiMoO4，α-NiMoO4和MoNi4的析氢性能依次提升，与理论计算中各物相所对应的水解离能垒依次降低相一致，证实了析氢活性依赖于催化剂物相结构的本质。该研究为合理设计和优化NiMo(O)催化剂提供参考。

关键词: 电催化, 分解水, 氢气, 钼酸镍, 物相

Abstract:

NiMo(O) catalysts show extremely low overpotential at high current density for the electrocatalytic hydrogen evolution reaction (HER). However, the real reason for the remarkable electrocatalytic activity is unclear. A new perspective for revealing the relation between the phase structures of the electrocatalysts and their electrocatalytic HER performance provides a deep insight into the nature of the HER. Herein, the dehydration and oxygenation of as-synthesized nickel molybdate hydrate (NiMoO4·nH2O) are discussed and confirmed to be critical for evolving the catalytic phase structures in the subsequent reduction treatment. The typical phase evolution processes of the electrocatalysts were investigated using thermogravimetric (TG) analysis and H2 temperature-programmed reduction (H2-TPR). The crystalline phases were identified through X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) analyses. The phases of the electrocatalysts during the electrochemical tests were confirmed by in situ electrochemical XRD characterization. Three typical crystalline phases, MoNi4, β-NiMoO4, and α-NiMoO4, corresponding to significantly different HER activities, were proposed. The β-NiMoO4 dominant electrocatalyst (NiMoO4-400air-H2) exhibited the worst performance for alkaline water reduction, and an improvement was observed for the α-NiMoO4 electrocatalyst (NiMoO4-500air-H2). The NiMoO4-300air-H2 electrode derived from NiMoO4·(n−x)H2O exhibited the most active phase (MoNi4) and the best electrocatalytic HER performance. Moreover, the intrinsic electrocatalytic HER performance obtained from the electrochemical active surface area (ECSA) normalized activities exhibits the same tendency as the geometrically normalized ones. Varied adsorption capacities of the H2O, OH, and H intermediate species for water reduction on these typical phases are assumed to be responsible for the significantly different HER performance of the NiMoO4-(T)air-H2 electrodes through density functional theory analysis. Poor adsorption of H, OH radicals, and H2O on β-NiMoO4 impedes the water dissociation process, which may be the reason that it exhibits the worst electrocatalytic hydrogen evolution activity. Optimized adsorption abilities of H, OH, and H2O on α-NiMoO4 benefit the water reduction kinetics, leading to an enhanced electrocatalytic HER performance. MoNi4 forms the strongest interactions with H2O, H, and OH species, contributing to the best electrocatalytic hydrogen evolution activity. Further analysis of the energy barrier of the water-splitting reaction shows that these three crystalline phases exhibit different water dissociation ability, which is attributed to their varied adsorption capacities of the intermediate species for water reduction. Among them, MoNi4 and β-NiMoO4 exhibit the lowest and highest water dissociation barriers, respectively, in line with their electrocatalytic hydrogen evolution activities. The phase-dependent HER activity identified in this work can provide guidelines for rationally designing and adjusting the structures of active NiMo(O) electrocatalysts.

Key words: Electrocatalysis, Water splitting, Hydrogen, Nickel molybdate, Crystalline Phase