Synergistic electrocatalytic oxygen reduction reactions of Pd/B4C for ultra-stable Zn-air batteries

Highly active and durable electrocatalysts are desired to promote oxygen reduction reactions (ORR) for Zn-air batteries. Here we report a promising catalyst of Pd nanoparticles supported on boron carbide (Pd/B4C) through a facile hydrothermal route. The Pd/B4C electrode not only shows the same onset potential of 0.96 V vs. RHE as the Pt/C electrode, but also an obviously larger limiting current density. More importantly, compared with noble metal electrodes, Pd/B4C shows higher power density (187 mW cm-2) and much more durable cycle life (up to 1333 h) in Zn-air batteries. To gain insight into the enhanced ORR activity by B4C support, first-principles computations reveal the synergistic effect between B4C and Pd; B4C could significantly promote O2 adsorption and splitting on Pd/B4C composites, while Pd particles on B4C have a major effect on the transformation of O* to OH-. The computations are consistent with the experimental characterizations. This work opens up a new avenue for seeking novel and durable electrocatalysts for Zn-air batteries with B4C substrates, which are chemically and electrochemically stable in hash alkaline electrolytes during operation.