Preparation And Electrochemical Properties Of Transition Metal Boride

The limit shortage and pollution problems of fossil fuels are becoming more and more serious.Hydrogen-dominated clean energy and new high-capacity electrochemical power sources have become a research trend,which need highly active electrocatalyst materials for water splitting and electrode materials with excellent property.Some transition metal borides such as cobalt boride show better catalytic activity for water electrolyzing,and high capacity as negative electrode in alkaline electrolyte.However,bimetallic borides have rarely been reported as catalytic materials and as positive electrode in alkaline batteries.In view of the above status and the property of borides,cobalt-nickel based bimetallic borides were selected as the research object.The electrochemical properties of cobalt-nickel bimetals as oxygen evolution reaction?OER?catalysts and positive electrode materials in alkaline battery were studied.And the corresponding reaction mechanisms were investigated.In this study,a series of bi-metallic boride catalysts based on Ni and Co were prepared,and their catalytic activities were evaluated.The synthesised Co-10Ni-B catalyst exhibited excellent activity for water splitting in 1 M KOH electrolyte.The over-potential for OER was 330 mV at a current density of 10 mA/cm²,which is much better than previously reported mono-metallic borides and even IrO₂.The synergistic effect of Co and Ni was proved by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy.The facile formation of critical intermediates CoOOH and NiOOH during the catalytic processes and a significant increase in surface area owing to the introduction of a second metal to mono-metallic boride were attributed to the superior catalytic performance of catalysts for oxygen evolution reaction.Co-10Ni-B-sp catalyst with a higher surface area was also synthesised to evaluate the effect of a high surface area on the catalytic activity.A lower over-potential of 310 mV for OER at a current density of 10 mA/cm² was achieved.A facile chemical reduction method was used to prepare of Co-Ni-B.The obtained products showed outstanding electrochemical performances as electrode materials in aqueous electrolytes at super high current densities.Co-Ni-B nanocomposite exhibited reversible specific capacity of 319.4 mAh/g,remarkable rate capability over 90%at 20A/g,and excellent cyclability with no obvious decay over 100 cycles.These excellent electrochemical performances were attributed to the combined action of nickel and cobalt in borides,where the cobalt improve the electrochemical reversibility and nickel enable the electrochemical activation of cobalt component,while introduction of boron will increase the electronic conductivity of the electrode materials.The high surface area of Co-Ni-B also facilitated the mass and charge transfer,which,in turn,boosted the electrochemical performances.