Catalytic Performance Promotion of Pd Cluster Towards H₂O₂ Production by Potential-Driven Coordination Adjustment

Electrochemical synthesis of hydrogen peroxide has been emerging as an appealing process for the onsite production of this chemically valuable oxidant, while its commercial application is still hindered by the development of efficient electrocatalyst. Herein, we design an efficient electrocatalyst for the electrochemical synthesis of H₂O₂ consisting of Pd cluster loading on hollow mesoporous carbon spheres (HMCS). Pd coordination environment is well designed with S in the first coordination sphere and O in the second coordination sphere. The as-prepared material exhibits superior performance with high H₂O₂ selectivity (maximum value: 99%) over a wide potential range of 0 to 0.6 V. Moreover, a high kinetics mass activity (4.059 A mg^-1 at 0.45V) of Pd_x/HMCS is achieved, which is almost three times larger than the state-of-the-art Pd-Hg alloy catalyst. What's more, in neutral electrolyte, Pd_x/HMCS also a positive onset potential of 0.647 V and high H₂O₂ selectivity of 84-93% within a wide potential range. The excellent performance can be attributed to the unique Pd cluster structure and optimized Pd coordination environment, especially the oxygen modification on HMCS support. In-situ Raman results reveal that under potentials, oxygen atoms transfer from the second coordination sphere (oxygen containing functional groups on HMCS) to the first coordination sphere (Pd-O bond). Density functional theory (DFT) calculations confirm that such oxygen coverage helps optimize the *OOH binding energy on Pd surface, resulting in significantly enhanced catalytic performance towards H₂O₂ production. This work reveals the structure difference between in-situ and ex-situ situations, proposes a new mechanism for the improved performance, and provides new insights into the future catalyst design.