In-Situ XAS Studies of the Reconstruction of Nickel Selenide OER Electrocatalysts

Nickel selenides are one of the state-of-the-art electrocatalysts for full water splitting and are especially efficient for catalyzing the oxygen evolution part reaction (OER) in alkaline media. They are cost-effective due to the consistency of earth-abundant elements. [1] Under OER conditions, nickel selenides are converted to the real catalytically active species nickel (oxy)hydroxides. [1,2]<br/>In this work, we investigated the OER performance of in-situ generated nickel (oxy)hydroxides from nickel selenides using in-situ X-ray absorption spectroscopy (XAS). Nickel selenides were electrodeposited on a gold-coated carbon paper and fluorescence XAS spectra were recorded using a home-designed cell [3] at different OER overpotentials. The as-deposited nickel selenides were first transformed via cyclic voltammetry (CV) under OER conditions to a nickel (oxy)hydroxide species. Afterward, the catalyst behavior was monitored during a series of chronoamperometry experiments at different OER overpotentials. In-situ X-ray near-edge spectroscopy (XANES) on the nickel edge was used to extract the oxidation states and electronic structure of the catalyst at each overpotential. [4] Furthermore, information about the local atomic structure of the active nickel centers (e.g., bond distances and coordination numbers) were extracted from the extended X-ray absorption fine structure (EXAFS) regions of the in-situ XAS spectra. [5] Additionally, we gained information about transformational and pseudo-capacitive processes of the catalyst from electrochemical impedance spectroscopy (EIS) [6] and related them to those extracted from XANES and EXAFS analyses. EIS spectra were recorded at each investigated OER overpotential before and after the CA experiments. With this combined approach, we have a better understanding of transformation processes in highly active nickel-selenides-based OER electrocatalysts under working conditions.<br/><br/>Literature:<br/><br/>[1] a) M. G. Walter et al., <i>Chemical reviews </i><b>2010, </b>110, <i>11</i>, 6446–6473; b) C. Tang et al., <i>Angewandte Chemie (International ed. in English) </i><b>2015</b>, <i>54</i>, 9351. <i>110</i>, 6446.; [2] S. Anantharaj, S. Noda, <i>International Journal of Hydrogen Energy </i><b>2020</b>, <i>45</i>, 15763.; [3] M. Wang et al., <i>Nano-Micro Lett.</i> <b>2019</b>, <i>11</i>, 47; [4] D.C. Koningsberger, R. Prins, <i>Wiley</i>, Book, <b>1988</b>; [5] J.J. Rehr et al., Phys. Chem. Chem. Phys. <b>2010</b>, <i>12(21)</i>, 5503–5513; [6] J. Linnemann et al., <i>ACS Catal. </i><b>2021, </b><i>11</i>, 5318.