AbstractDeveloping highly efficient and cost-effective oxygen evolution reaction (OER) electrocatalysts is critical for many energy devices. While regulating the proton-coupled electron transfer (PCET) process via introducing additive into the system has been reported effective in promoting OER activity, controlling the PCET process by tuning the intrinsic material properties remains a challenging task. In this work, we take double perovskite oxide PrBa_0.5Sr_0.5Co_1.5Fe_0.5O_5+δ (PBSCF) as a model system to demonstrate enhancing OER activity through the promotion of PCET by tuning the crystal orientation and correlated proton diffusion. OER kinetics on PBSCF thin films with (100), (110), and (111) orientation, deposited on single crystal LaAlO₃ substrates, were investigated using electrochemical measurements, density functional theory (DFT) calculations, and synchrotron-based near ambient X-ray photoelectron spectroscopy. The results clearly show that the OER activity and the ease of deprotonation depend on orientation and follow the order of (100) > (110) > (111). Correlated with OER activity, proton diffusion is found to be the fastest in the (100) film, followed by (110) and (111) films. Our results point out a way of boosting PCET and OER activity, which can also be successfully applied to a wide range of crucial applications in green energy and environment.