Engineering the electronic structure of atomically dispersed p-block bismuth sites via multi-shells tuning effect for boosting oxygen reduction reaction

Main-group metal (s- and p-block) single atom catalysts (SACs), in which metal cations stabilized by nitrogen atoms (metal-N_x moieties), have emerged as efficient electrocatalysts for oxygen reduction reactions (ORR). However, the closed d shells over main-group metals-based catalysts hinder design of more efficient catalysts than state-of-the-art non-precious Fe single atom catalysts (Fe₁/NC). Here we report a p-block Bi-based single-atom electrocatalyst with electronic structure controlled by multi-shell that exhibits high catalytic performance for ORR in alkaline media. Our data suggest the catalyst is composed of single Bi atoms coordinated with four nitrogen atoms on sulfur-phosphorus co-doped carbon nanocages (BiN₄/PSNC). The catalyst gives a high half-wave potential of 0.94 V for 4 e⁻ ORR and performs negligible attenuation after 10,000 cycles. In addition, the Zn-air battery assembled by BiN₄/PSNC achieves a remarkable peak power density of 452.8 mW·cm⁻², exceeding other reported main-group metal SACs and most d-band metal SACs. A range of analytical techniques combined with density functional theory calculations reveal that the introduction of S and P sites induces significant electronic modulations to the BiN₄ active sites, P and S doping promote the electrical activity of BiN₄ and improve the overall intersite electron transfer within BiN₄/PSNC optimizing the adsorption energy of the oxygen intermediates. The 4e⁻ ORR activity was improved. This work offers a unique pathway in designing main-group metals-based SACs for energy conversion devices.