Enhanced Electrocatalytic Activities of In Situ Produced Pd/S/N-Doped Carbon in Oxygen Reduction and Hydrogen Evolution Reactions

We report an electrocatalyst of Pd nanoparticles (NPs) supported on a carbon sphere nanoarchitecture doped with sulfur (S) and nitrogen (N) atoms (PdSNC), which is designed by exploiting a palladium-rubeanic acid (Pd-RA) coordination polymer as a precursor, followed by calcination. The synthesized Pd-RA coordination polymer, as a new precursor material, is the combination of Pd, S, N, and C in its structural backbone. The in situ formation of PdSNC was achieved by controlled carbonization of the Pd-RA precursor. The doping of S and N into carbon networks modulates the electronic structure and strengthens the affinity of the Pd NPs with the carbon surface, which reveals the improved electrical and electrochemical performance of the PdSNC catalyst. The electrochemical investigation of the oxygen reduction reaction and the hydrogen evolution reaction (ORR and HER, respectively) reveals that the combination of S and N in Pd carbon is more active than mere Pd carbons. The combined benefits from the binary heteroatoms (S and N) in the carbon texture are offered to modulate the electronic structure and stabilize Pd NPs, thus augmenting the stable electrocatalytic activity as an alternative to expensive commercial PtC. The half-wave potential of the ORR for PdSNC was 0.869 V with 4.0 electron transfer, which is better than those of PdC (0.791 V), PtC (0.830 V), and its counterpart SNC (0.786 V) catalysts. Besides, the overpotential of PdSNC showing a great promise as the HER catalyst to achieve a current density of 10 mA.cm(-2) is only 0.030 V, which is much better than that of PdC and comparable to that of PtC. This all-in-one-step strategy (doping and PdC formation) is a promising approach to design heteroatoms-stabilized carbon-metal composites with a high electrocatalytic performance for sustainable energy applications.