Biochar-based oxygen electrocatalysts for advanced Zn-air batteries: Mechanisms, applications, and prospects

Biochar is a biogenic carbon material with abundant sources and superior performance. The preparation of functional biochar with specific structures (such as quantum dots, nanofibers, hierarchical porous structures) from biomass materials holds substantial scientific significance for the field of electro-catalysis. This article depicts the unique advantages inherent to various types of biomass, exploring the potential applications of derived biochar for oxygen electro-catalysts. This may offer new solutions to the issues of high costs and scarce resources associated with traditional precious metal catalysts. The structural diversity and molecular tunability of biomass make it an ideal raw material for the preparation of three-dimensional, functional, self-doped, and self-assembled carbon materials. This review is organized around the core framework of a “bidirectional regulation” strategy: First, on the forward path, it systematically outlines the various methods of transforming biomass into functional biochar and delves into the mechanisms by which the inherent structure and composition of biomass precursors affect the performance of derived biochar. Then, on the reverse path, it focuses on how to reverse-engineer and optimize the material properties of biochar guided by the target oxygen electro-catalytic performance, thus constructing a rational design loop from performance requirements to precursor selection. This review provides theoretical guidance for the preparation of biochar-based oxygen electro-catalysts, and also offers a new perspective on the preparation of carbon materials based on biomass.