Ultrathin Porous Pd Metallene with Amorphous/Crystalline Phase Coexitence as Electrocatalysts for the Oxygen Reduction Reaction

The development of efficient nonplatinum electrocatalysts with enhanced oxygen reduction reaction (ORR) activity and stability is of crucial importance for the commercial application of fuel cells and metal–air batteries. Metallenes exhibit excellent performance in energy and catalysis due to their unique physicochemical and electronic properties. In particular, the ultrahigh proportion of under-coordinated metal atomic sites in metallenes enhances the atom utilization and intrinsic activity, which endows them with considerable potential for catalytic applications. Herein, the synthesized two-dimensional (2D) ultrathin porous Pd metallene with amorphous/crystalline phase coexistence exhibits enhanced alkaline oxygen reduction properties, as evidenced by four-electron selectivity, lower overpotential (E1/2 = 0.944 V), high mass activity (MA = 1.44 mA/μgPd), and solid stability (only loss of 7 mV in half-wave potential after 10,000 potential cycles). Such high performance of Pd metallene is attributed to amorphous/crystalline heterophases, 2D morphology, and porous structure. DFT calculations demonstrate that the ORR catalytic performance can be effectively promoted by the amorphous structure with a modulated electronic structure. The amorphous/crystalline coexisting porous Pd metallene with excellent catalytic performance can provide the reference for metallene materials design in various fields. This study presents a scientific basis to understand the mechanism of 2D amorphous phase nanostructures for boosting the electrocatalytic performance.