NANOSTRUCTURED ELECTROCATALYSTS FOR OXYGEN REDUCTION AND EVOLUTION REACTIONS
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Highly active, low cost and durable electrocatalysts are desired for the development and commercialization of fuel cells and metal-air batteries. The efficiency of these devices is significantly limited by the activation of oxygen-involved reactions, namely oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Precious metals (such as Pt) and metal oxides (such as RuO2) are traditional electrocatalysts for ORR and OER, respectively. However, the electrocatalytic performance of these precious metal-based nanomaterials is still hindered by their scarcity, high cost, insufficient activity and poor durability. Recently, developing cost-efficient and highly active electrocatalysts to replace the precious metals and oxides have obtained increasing attentions. To enhance the performance of ORR electrocatalysis, formation of PtM (M=Fe, Co, Ni, Cu) is one of most widely used strategies. The utilization of PtM can not only decrease the overall cost but improve the catalytic activity due to the synergistic effect between Pt and M. In addition, porous carbon-based nanomaterials, such as heteroatom-doped carbon, metal-nitrogen-carbon (M-N-C) nanostructures and carbon/nonprecious metal hybrids, have also been demonstrated to be promising candidates for ORR catalysis in alkaline media. These porous catalysts can effectively reduce the cost because of the absence of precious metals. Besides, the unique porous structures are favorable for mass transport and electron transfer, thus improving ORR catalytic performance. For OER electrocatalysis, a multitude of efforts have been devoted to investigate earth-abundant and highly active catalysts, such as transition metal-based nanomaterials (alloys, oxides, phosphides, phosphates, hydroxides, etc.). The corresponding OER catalytic performance can be effectively improved by tailoring the intrinsic nature of the catalysts as well as forming sufficient active sites, which can be achieved by tuning the elemental composition and increasing the surface area. Herein, a large variety of nanostructured electrocatalysts with different composition and morphology were designed and synthesized. Thanks to their compositional and morphological advances, these catalysts have been demonstrated to be active for ORR or OER.