Exploring the Structural Forms and Catalytic Potential of Carbon Nanomaterials in Metal–Air Batteries

Metal–air batteries are highly valued for their exceptional energy efficiency and affordability. Identifying suitable electrode materials is crucial to fully harness their potential. Carbon nanomaterials, renowned for their excellent conductivity, vast specific surface area, robust stability, and minimal volume expansion, have emerged as a preferred choice for many. However, early characterization techniques struggle to precisely pinpoint catalytic active sites across various electrocatalytic reactions, making it challenging to comprehend the experimental impact of different active site types on these reactions. This has posed a significant obstacle to unveiling the catalytic mechanism and developing efficient catalysts. With advancements in characterization methods, studies on carbon nanomaterials have progressed rapidly. Herein, the structure of carbon nanomaterial catalysts are reshaped by the researchers to improve catalytic efficiency, resulting in four distinct structural forms: metal-free carbon–based materials, atomically dispersed metal carbon-based materials, metal nanoparticles encapsulated in carbon-based materials, and metal nanoparticles supported on carbon-based materials. In this review, the features of these structural forms and their application contexts, detailing the synthesis methods and catalytic effects of each form, are highlighted. This article concludes with an overview of recent advancements and future directions in the characterization techniques of carbon materials.