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The emerging of single‐atom catalysts (SACs) offers a great opportunity for the development of advanced energy storage and conversion devices due to their excellent activity and durability, but the actual mass production of high‐loading SACs is still challenging. Herein, a facile and green boron acid (H3BO3)‐assisted pyrolysis strategy is put forward to synthesize SACs by only using chitosan, cobalt salt and H3BO3 as precursor, and the effect of H3BO3 is deeply investigated. The results show that molten boron oxide derived from H3BO3 as ideal high‐temperature carbonization media and blocking media play important role in the synthesis process. As a result, the acquired Co/N/B tri‐doped porous carbon framework (Co–N–B–C) not only presents hierarchical porous structure, large specific surface area and abundant carbon edges but also possesses high‐loading single Co atom (4.2 wt.%), thus giving rise to outstanding oxygen catalytic performance. When employed as a catalyst for air cathode in Zn‐air batteries, the resultant Co–N–B–C catalyst shows remarkable power density and long‐term stability. Clearly, our work gains deep insight into the role of H3BO3 and provides a new avenue to synthesis of high‐performance SACs. [ABSTRACT FROM AUTHOR]

Lattice‐strained Bi2S3 with 3D hierarchical structures are prepared through a top‐down route by a topotactic transformation. High‐resolution transmission electron microscopy and X‐ray diffraction (XRD) confirm the lattice spacing is expanded by prolonged sulfuration. Performance studies demonstrate that Bi2S3 with the largest lattice expansion (Bi2S3‐9.7%, where 9.7% represents the lattice expansion) exhibits a greater electrocatalytic hydrogen evolution reaction (HER) activity compared to Bi2S3 and Bi2S3‐3.2%. Density functional theory calculations reveal the expansion of the lattice spacing reduces the bandwidth and upshifts the band center of the Bi 3d orbits, facilitating electron exchange with the S 2p orbits. The resultant intrinsic electronic configuration exhibits favorable H* adsorption kinetics and a reduced energy barrier for water dissociation in hydrogen evolution. Operando Raman and post‐mortem characterizations using XRD and X‐ray photoelectron spectroscopy reveal the generation of pseudo‐amorphous Bi at the edge of Bi2S3 nanorods of the sample with lattice strain during HER, yielding Bi2S3‐9.7%‐A. It is worth noting when Bi2S3‐9.7%‐A is assembled as a positive electrode in an asymmetric supercapacitor, its performance is greatly superior to that of the same device formed using pristine Bi2S3‐9.7%. The as‐prepared Bi2S3‐9.7%‐A//activated carbon asymmetric supercapacitor achieves a high specific capacitance of 307.4 F g−1 at 1 A g−1, exhibiting high retention of 84.1% after 10 000 cycles. [ABSTRACT FROM AUTHOR]