Pd@SmMn<sub>2</sub>O<sub>5</sub> as an Efficient Oxygen Reduction Reaction Catalyst via Triggering the Synergistic Effect between Dual Crystal Fields in Mullite
Chunning Zhao, Ansheng Wang, Shan Gao, Lijin Wang, Meng Yu, Zhi Yang, Dawei Shao, Juntao Niu, Geng Wang, Weifang Li, Weichao Wang
Abstract
The cooperation among different surface coordination environments is beneficial to reach a moderate interaction with the oxygen intermediates and therefore achieve an optimal electrochemical oxygen reduction reaction (ORR) activity. A facilely effective strategy is essential to regulate the electronic structure and then the ratio of Mn3+ to Mn4+ in the intrinsically strong Mn–O bonding SmMn2O5. In this work, a two-step photochemical reduction method was adopted to load the Pd nanoparticles on the SmMn2O5 nanorods to form an atomic interface contact. The optimized catalyst 7.5 wt % Pd@SmMn2O5 shows an excellent activity with the half-wave potential 0.83 V (vs RHE) and the charge-transfer resistance ∼38 Ω smaller than that of commercial platinum. The electrons transferring from Pd to p-type SmMn2O5 at the interface contribute to the moderate d-band center and Mn valence and then the neither too strong nor too weak interaction with oxygen intermediates. The accumulated electrons on the conduction band of mullite occupy the anti-bonding states of oxygen in mullite and then activate more oxygen, which favors the labile oxygen participant adsorbate evolving mechanism (LAM) for the ORR process. The assembled Zn–air battery exhibits a high peak power density of ∼236 mW/cm2 and a large open-circuit potential of ∼1.43 V. This work provides insights into the activity optimization of the intrinsically stable catalysts from the aspect of the metal–semiconductor interface.