Highly Active and Durable Transition Metal Oxide-Based Oxygen Electrode Catalysts for Unitized Reversible Fuel Cells

Abstract

Facing with the increasing environmental concerns for global warming and environmental pollutions, it is essential to develop renewable and sustainable energy sources to substitute traditional fossil fuel-based technologies. As a major candidate technology, unitized reversible fuel cells (URFCs) are recognized as a promising electrochemical energy conversion device due to their high energy efficiency and negligible carbon emissions [1]. However, the low electrocatalytic activity related to the large overpotential loss for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the key technical issue for the development of URFCs [2]. Until now, precious metal-based catalysts (e.g., Pt/C, Ir/C, and IrO2) have been used for OER and ORR in URFCs due to high electrocatalytic activity [3]. Nevertheless, making commercialization of URFCs has hampered by the scarcity and limited durability of these materials [4, 5]. In order to solve these technical barriers, non-precious transition metal oxide based materials have considered as promising alternatives for bifunctional OER and ORR electrocatalysts because of their low cost, earth-abundance, and long-term stability [6]. However, transition metal-based oxygen catalysts have several issues such as low electrical conductivity, small surface area, and low electroactivity. Herein, as main strategies to improve bifunctional electrocatalytic activity for OER and ORR, other transition metals are doped to increase intrinsic property of oxide materials with hybridizing with highly conductive carbonaceous materials as supporting material. The synthesized catalysts are analyzed by various physicochemical and electrochemical analysis tools [7. 8].