Promoted surface reconstruction of amorphous nickel boride electrocatalysts by boron dissolution for boosting the oxygen evolution reaction†

Abstract

Transition metal borides (TMBs) are promising OER electrocatalysts in alkaline solution. Surface reconstruction and boron dissolution have been widely observed for TMBs during the OER; however, the role of boron dissolution in the surface reconstruction and the OER performance remains unclear. Herein, amorphous nickel boride (NiB) was synthesized and its OER performances in 1 M KOH solution were investigated with a particular focus on revealing the critical role of boron dissolution during the OER. A remarkable drop in the OER overpotential at 10 mA cm⁻² (η₁₀), i.e., ∼40 mV, during chronopotentiometry over 4–6 h was observed. By a combination of electrochemical tests, in situ Raman spectroscopy and DFT calculations, we revealed that boron dissolution facilitated the exposure of more nickel active sites, reduced the oxidation potential of Ni²⁺/Ni³⁺, and promoted surface reconstruction into γ-NiOOH. The dissolved boron, in the form of BO₂⁻, adsorbed on the reconstructed γ-NiOOH to reduce the reaction energy barrier of the potential-determining step, and thus enhanced the OER activity. Benefiting from boron dissolution and surface reconstruction, NiB on nickel foam substrates demonstrates a superior activity (η₁₀ = 279 mV) after 10 hour chronopotentiometry, which is comparable to that of most reported multi-cation TMB catalysts.