jats:pThe 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 (Hjats:sub3</jats:sub>BOjats:sub3</jats:sub>)‐assisted pyrolysis strategy is put forward to synthesize SACs by only using chitosan, cobalt salt and Hjats:sub3</jats:sub>BOjats:sub3</jats:sub> as precursor, and the effect of Hjats:sub3</jats:sub>BOjats:sub3</jats:sub> is deeply investigated. The results show that molten boron oxide derived from Hjats:sub3</jats:sub>BOjats:sub3</jats:sub> 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 jats:italicwt.</jats:italic>%), 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 Hjats:sub3</jats:sub>BOjats:sub3</jats:sub> and provides a new avenue to synthesis of high‐performance SACs.</jats:p>