In Situ Engineering of Pd Nanosponge Armored with Graphene Dots Using Br– toward High-Performance and Stable Electrocatalyst for the Hydrogen Evolution Reaction

In this study, we report a facile synthetic pathway to three-dimensional (3D) Pd nanosponge-shaped networks wrapped by graphene dots (Pd@G-NSs), which show superior electrocatalytic activity toward the hydrogen evolution reaction (HER) and exhibited excellent long-term stability in acidic media. Pd@G-NSs were synthesized by simply mixing Pd precursors, reducing agent, carbon dots (Cdots), and Br– ion at 30 °C. Experimental results and density functional theory (DFT) calculations suggested that the Br– ions played an essential role in accelerating the exfoliation of Cdot, supplying graphene layers, which could wrap the nanosponge-shaped Pd and finally form Pd@G-NS. In the absence of the Br– ions, only aggregated Pd nanoparticles (NPs) were formed and randomly mixed with Cdots. The resultant Pd@G-NS exhibited a high electrochemically active surface area and accelerated charge transport characteristics, leading to its superior electrocatalytic activity toward the HER in acidic media. The HER overpotential of Pd@G-NS was 32 mV at 10 mA cm–2, and the Tafel slope was 33 mV dec–1. Furthermore, the unique Pd@G-NS catalyst showed long-term stability for over 3000 cycles in acidic media as well, owing to the protection of Pd nanosponges by graphene dot wrapping. The overall HER performance of the Pd@G-NS catalyst exceeded that of commercial Pt/C.