Understanding the Surface Reconstruction on Ternary W_x CoB_x for Water Oxidation and Zinc-Air Battery Applications

Here, the synthesis of a series of pure phase metal borides is reported, including WB, CoB, WCoB, and W₂ CoB₂ , and their surface reconstruction is studied under the electrochemical activation in alkaline solution. A cyclic voltammetric activation is found to enhance the activity of the CoB and W₂ CoB₂ precatalysts due to the transformation of their surfaces into the amorphous CoOOH layer with a thickness of 3-4 nm. However, such surface transformation does not happen on the WB and WCoB due to their superior structure stability under the applied voltage, highlighting the importance of metal components for the surface reconstruction process. It is found that, compared with CoB, the W₂ CoB₂ surface shows a quicker reconstruction with a larger active surface area due to the selective leaching of the W from its surface. In the meantime, the metallic W₂ CoB₂ core underneath the CoOOH layer shows a better promotion of its oxygen evolution reaction (OER) performance than CoB. Therefore, the ternary W₂ CoB₂ shows better OER performance than the CoB, as well as the WB and WCoB. It is also found that the mixture of W₂ CoB₂ with Pt/C as the catalysts in air electrode for rechargeable Zn-air battery (ZAB), shows better performance than the IrO₂ -Pt/C couple-based ZAB.