No abstract

Single-atom catalysts (SACs) have attracted significant attention due to their superior catalytic activity and selectivity. However, the nature of active sites of SACs under realistic reaction conditions is ambiguous. In this work, high loading Pt single atoms on graphitic carbon nitride (g-C 3 N 4)-derived N-doped carbon nanosheets (Pt 1 /NCNS) is achieved through atomic layer deposition. Operando X-ray absorption spectroscopy (XAS) is performed on Pt single atoms and nanoparticles (NPs) in both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). The operando results indicate that the total unoccupied density of states of Pt 5d orbitals of Pt 1 atoms is higher than that of Pt NPs under HER condition, and that a stable Pt oxide is formed during ORR on Pt 1 /NCNS, which may suppress the adsorption and activation of O 2. This work unveils the nature of Pt single atoms under realistic HER and ORR conditions, providing a deeper understanding for designing advanced SACs.

Shape-controlled Pt-based bimetallic nanocrystals with ultrathin Pt-rich surfaces are appealing electrocatalysts for some key electrochemical reactions such as the oxygen reduction reaction (ORR) because of the synergistic tuning of topological atom configuration and strengthened electronic effects. However, it is rather challenging to fabricate such particular structures that can remain intact in harsh electrochemical environments, as such Pt-based nanocatalysts are unable to simultaneously achieve both unparalleled activity and robust stability. Here, a facile surface engineering strategy is proposed and employed to atomically tailor the near-surface structure of the Pt1.5Ni octahedra. The engineered Pt–Ni octahedra consist of an ultrathin Pt-rich shell (∼two atomic layers) and Pt-rich bulk composition. The optimized octahedral catalyst exhibits superior specific and mass activity (7.7 mA/cm2 Pt and 1.9 A/mg Pt at 0.9 V) for ORR, ∼20 and ∼10 times higher than commercial Pt/C, respectively. The ligand and strain effects arising from the near-surface engineering are unraveled to be responsible for the remarkable ORR activity. Moreover, it shows robust stability with just 9.2% decay in mass activity after accelerated degradation tests (ADTs), as its compositional nature prevents surface Pt atoms and interior Ni atoms from diffusion and dissolution, compared with a decrease of 33% for commercial Pt/C. Our atomical engineered surface strategy illustrates a facile and effective design for a class of Pt-based nanocatalysts with excellent activity and stability.

The essence of developing a Pt‐based single‐atom catalyst (SAC) for hydrogen evolution reaction (HER) is the preparation of well‐defined and stable single Pt sites with desired electrocatalytic efficacy. Herein, we report a facile approach to generate uniformly dispersed Pt sites with outstanding HER performance via a photochemical reduction method using polyvinylpyrrolidone (PVP) molecules as the key additive to significantly simplify the synthesis and enhance the catalytic performance. The as‐prepared catalyst displays remarkable kinetic activities (20 times higher current density than the commercially available Pt/C) with excellent stability (76.3 % of its initial activity after 5000 cycles) for HER. EXAFS measurements and DFT calculations demonstrate a synergetic effect, where the PVP ligands and the support together modulate the electronic structure of the Pt atoms, which optimize the hydrogen adsorption energy, resulting in a considerably improved HER activity.