Low-cost decorated biochar derived from sweet sorghum stalks as catalyst support potential for PEMFCs

The utilisation of Proton exchange membrane fuel cells (PEMFCs) requires costly, durable carbon support materials to replace the traditional carbon black materials and reduce Pt loading. Biochar serves as an environmentally benign and economic alternative material produced from the pyrolysis of biomass. It is associated with remarkable properties such as inherent porosity, abundance and tailored properties. The current review therefore evaluates the potential of using sweet sorghum stalk biochar as a catalyst support material, focusing on green synthesis routes, and modification strategies to enhance its performance. This current review offers extensive summary into production methods of biochar, pretreatment and activation techniques, surface functionalisation which includes heteroatom doping and oxidation and the role of carbon support properties such as porosity, conductivity, and corrosion in PEMFCs. The key electrochemical performance are discussed in relation to the support material such as onset potential, mass activity, electrochemical active surface area (ECSA) electron number and stability/durability. Literature results have shown that when the pyrolysis temperature and heteroatom doping are optimised then the BET surface area, hierarchical pores are created, this optimisation also introduces functional groups. However, there are significant gaps when it comes to scaling of green synthesis methods, long term electrochemical stability in PEMFCs, and direct comparison of biochar with Pt/C. Overall, sweet sorghum stalks presents a low cost, and sustainable alternative for the existing PEMFCs catalyst supports, given that the modification strategies are tailored to balance activity, stability and manufacturability.