Design strategies of Pd-based electrocatalysts for efficient oxygen reduction

Oxygen reduction reaction (ORR) occurs at the cathode of fuel cells and metal–air batteries, but usually suffers from sluggish kinetics. To solve this issue, efficient electrocatalysts are highly desired. Palladium (Pd)-based nanomaterials, as the most promising substitute of platinum (Pt), exhibit superior activity and stability in ORR electrocatalysis. The delicate regulation of the structure and/or composition shows great potential in improving the electrocatalytic ORR performance of Pd-based nanomaterials. In this review, we retrospect the recent advance of Pd-based ORR electrocatalysts, and analyses the relationship between nanostructure and catalytic performance. We start with the ORR mechanism and indicators of ORR performance in both alkaline and acidic media, followed by the synthetic methods for Pd-based nanoparticles. Then, we emphasize the design strategies of efficient Pd-based ORR catalysts from the perspective of composition, crystal phase, morphology, and support effects. Last but not least, we conclude with possible opportunities and outlook on Pd-based nanomaterials toward ORR. Graphical abstract: [Figure not available: see fulltext.]