Recent Progress in Development of Cost Effective and Highly Efficient Pt Group Metal Free ORR and HER Electrocatalysts for Next Generation Energy Devices

The requirement of clean and sustainable energy technology continues to rise as the energy supply crisis and environmental concerns worsen. As a result, new sources of alternative, stable, cost-effective, clean energy generation and storage devices need to be developed immediately. Several emerging cathode-based energy conversion and storage technologies rely on either the oxygen reduction reaction (ORR) or the hydrogen evolution reaction (HER) as their primary routes. Lately, scientists have paid much attention to enhancing the ORR and HER reaction rate and storing energy effectively by fabricating low-cost, highly active, and long-lasting electrocatalysts. Traditional electrocatalysts have relied on platinum (Pt), but its expensive price, limited durability, low selectivity, and poor alcohol tolerance have prompted the exploration of more cost-effective and promising catalysts. Recent studies have shown that electrocatalysts based on elements other than the platinum group metals (Ni, Cu, Fe, Co, Mn, etc.) exhibit remarkable ORR and HER catalytic efficacy and stability. In addition, carbon-based materials including carbon nanotubes (CNTs), graphite, diamond, graphene, and other carbon allotropes with high ORR catalytic activity are becoming increasingly significant due to their low cost and absence of metals. This review delves into the expanding area of ORR and HER electrocatalysts, summarizing recent developments in the fields of non-precious metal-based electrocatalysts, carbon-based electrocatalysts, and heteroatom doped carbon materials, and discussing the difficulties and future prospects of potential Pt-group metal alternatives.