Abstract
Metallene is considered as an emerging family of electrocatalysts due to its atomically layered structure and unique surface stress. Here we propose a strategy to modulate the Bader charge transfer (BCT) between Pd surface and oxygenated intermediates via p-d electronic interaction by introducing single-atomp-block metal (M = In, Sn, Pb, Bi) into Pd metallene nanosheets towards efficient oxygen reduction reaction (ORR). X-ray absorption and photoelectron spectroscopy suggests that doping p-block metals could facilitate electron transfer to Pd sites and thus downshift the d-band center of Pd and weaken the adsorption energy of O intermediates. Among them, the developed Bi-Pd metallene shows extraordinarily high ORR mass activity of 11.34 A mgPd-1 and 0.86 A mgPd-1 at 0.9 V and 0.95 V in alkaline solution, respectively, representing the best Pd-based ORR electrocatalysts ever reported. In the cathode of a Zinc-air battery, Bi-Pd metallene could achieve an open-circuit voltage of 1.546 V and keep stable for 760 h at 10 mA cm-2. Theoretical calculations suggest that the BCT between Pd surface and *OO intermediates greatly affects the bond length between them (dPd-*OO) and Bi doping could appropriately reduce the amount of BCT and stretch the dPd-*OO, thus enhancing the ORR activity.
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