Pt21(C4O4SH5)21 clusters: atomically precise synthesis and enhanced electrocatalytic activity for hydrogen generation

Highlights: • Atomically precise Pt₂₁(C₄O₄SH₅)₂₁nanoclusters are synthesized at room temperature. • The Pt₂₁ clusters loaded on rGO with a clean surface can serve as efficient electrocatalysts. • With ultra-low mass loading, the Pt₂₁ clusters show higher catalytic activity than Pt/C for the HER. • Metal clusters have promising application in electrocatalysts for clean energy devices. -- Abstract: How to effectively enhance the catalytic performance and simultaneously reduce the usage of Pt-based catalysts is always the goal of catalyst design for electrochemical energy devices. Platinum nanoclusters (Pt NCs) have aroused massive concerns in recent years because of the excellent activity of Pt-based materials themselves and the unique physical and chemical properties of nanoclusters. However, the studies on the synthesis, properties and applications of Pt NCs have been rarely reported. Here, we report a simple avenue to synthesize Pt nanoclusters through using K₂PtCl₄ as precursor and mercaptosuccinic acid (MSA) as not only ligand but also the reducing agent at the room temperature. Based on the matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS), the obtained Pt NCs have the composition of Pt₂₁(C₄O₄SH₅)₂₁. By loading the Pt NCs on reduced graphene oxide nanosheets (rGO) and the following removal of MSA ligands upon annealing treatment, the obtained surface-clean Pt NCs/rGO exhibits excellent hydrogen evolution reaction (HER) catalytic performance and superior stability with Pt loading as low as 0.8 wt%. Especially, the HER mass catalytic activity of the Pt NCs/rGO is much higher than that of the 20.0 wt% commercial Pt/C catalyst. Meanwhile, this kind of cluster catalyst also shows large exchange current density (574 µA• cm⁻²) and high turn-over frequency (1.19 s⁻¹). The experimental result in this work clearly indicates that Pt catalyst on cluster scale can obviously improve the catalytic performance. Therefore, this study provides an effective avenue to enhance the utilization of noble metals and to develop high-performance and cost-effective catalysts.