Surface Structural Engineering of Nickel for Improved Hydrogen Electrocatalytic Activity in Alkaline Electrolytes

Developing stable and active alkaline non-noble metal hydrogen electrocatalyst is fundamentally important for the commercialization of anion exchange membrane-based fuel cells (AEMFCs) and water electrolyzers (AEMWEs) as they are considered the only replaceable alternatives to the state-of-the-art proton exchange membrane-based electrolyzers and fuel cells. [1,2] Nickel (Ni) based catalysts are the most investigating non-precious metal catalyst among the transition metals for hydrogen oxidation reaction (HOR)/hydrogen evolution reaction (HER) in alkaline medium at present. [3] However, the activity of these catalyst is not yet reachable to the precious metal-based catalyst, till date. Researcher are focusing on the modification of nickel surface like NiO, Ni(OH) 2 etc., and alloying transition metals such as Cr, Cu, Mo, W, Fe, Sn etc., for achieving high catalytic activity. [4,5,6] In this report, we investigate how surface structural changes of nickel using different nickel hydroxides enhance the hydrogen electrocatalytic activity in alkaline medium. Figure 1 shows schematic illustration of nickel catalysts with different nickel hydroxide surfaces. A thin layer of alpha nickel hydroxide on nickel catalyst surface (a-Ni(OH) 2 /Ni) prepared by two different approaches, 1) an electrochemically formed alpha nickel hydroxide on nickel nanoparticles (EC-a-Ni(OH) 2 /Ni) and 2) the particle catalyst prepared by partial reduction of nickel hydroxide to form a-Ni(OH) 2 /Ni catalyst. We have also prepared the catalysts of nickel alone (Ni) and electrochemically formed beta nickel hydroxide on nickel (EC-b-Ni(OH) 2 /Ni). The peaks appeared at 485 cm −1 and two broad peaks at 382 cm −1 and 582 cm −1 in Raman spectra (Figure 1B) confirm the formation alpha and beta nickel hydroxide on nickel surface after electrochemical treatment, respectively. Electrocatalytic activity of the catalysts tested in 0.1 M KOH shows that EC-a-Ni(OH) 2 /Ni shows enhanced catalytic activity for both HOR and HER compared with Ni and EC-b-Ni(OH) 2 /Ni. Moreover, the particle catalyst, a-Ni(OH) 2 /Ni with higher surface area shows further enhanced HOR and HER activities in alkaline medium. References Song, W. Li, J. Yang, G. Han, P. Liao and Y. Sun, Nat Commun, 2018 9 , 4531. Sun, P. Zhao, Y. Yang, Z. Li and W. Sheng, ACS Catal . 2023, 13 , 7, 4127–4133. Fu, Y. Li, N. Yao, F. Yang, G. Cheng, and W. Luo, ACS Catal. 2020, 10 , 13, 7322–7327. Men, X. Su, P. Li, Y. Tan, C. Ge, S. Jia, L. Li, J. Wang, G. Cheng, L. Zhuang, S. Chen and W. Luo, J. Am. Chem. Soc . 2022, 144 , 28, 12661–12672. Tüysüz, Acc. Chem. Res . 2024, 57 , 4, 558–567. Acknowledgement This presentation is based on results obtained from a project commissioned by JST Innovative GX Technology Creation Project (GteX), JPMJGX23H0, and a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO), JPNP20003. Figure 1