Ligand-regulated Ni-based coordination compounds to promote self-reconstruction for improved oxygen evolution reaction

Ni-based coordination compounds, during the oxygen evolution reaction (OER), self-reconstruct to produce NiOOH, which are the real active sites. Thus, encouraging the self-reconstruction of pre-catalysts to generate more NiOOH species has emerged as an effective strategy for enhancing the activity. In this research, we utilized three coordination compounds, Ni(N(CN)₂)₂, Ni(NCN), and Ni(HNCN)₂, to examine the effect of three distinct ligands (-N(CN)₂-, -HNCN-, and -NCN-) on the local electronic structure of coordinated Ni, aiming to promote the degree of self-reconstruction during the OER. XPS studies and in situ Raman spectroscopy revealed a significant relationship between the electron-donating properties of coordinated Ni and the self-reconstruction abilities of the pre-catalysts. Notably, Ni coordinated with -N(CN)₂- exhibits a high tendency to donate electrons, leading to facile reconstruction of Ni(N(CN)₂)₂ into Ni(OOH)-(N(CN)₂). As a result, Ni(OOH)-(N(CN)₂) displays high OER activity (264 mV @ 10 mA cm⁻² and Tafel slope of 40.80 mV dec⁻¹) in comparison to Ni(OOH)-(NCN) (290 mV @ 10 mA cm⁻² and Tafel slope of 55.63 mV dec⁻¹) and Ni(OOH)-(HNCN) (307 mV @ 10 mA cm⁻² and Tafel slope of 77.70 mV dec⁻¹). These findings offer new perspectives on designing and developing innovative catalysts to enhance OER efficiency.