Promoted surface reconstruction of amorphous nickel boride electrocatalysts by boron dissolution for boosting 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 OER, however, the role of boron dissolution on 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 interest on revealing the critical role of boron dissolution during OER. A remarkable drop of the OER overpotential at 10 mA·cm-2 (η10), i.e., ~ 40 mV, during chronopotentiometry in 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 the 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. Beneficial 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 most of the reported multiple-cation TMBs catalysts.