Silver-tungsten carbide nanohybrid for efficient electrocatalysis of oxygen reduction reaction in microbial fuel cell

Microbial fuel cell (MFC) is able to produce electricity from organic compounds upon anodic electrochemically active microorganisms (negative electrode) and cathodic oxygen reduction reaction (ORR, positive electrode). The diminution in ORR activity associated with the pH-neutral electrolyte degrades the cathode performance of MFC. To optimize the thermodynamic process of ORR involving dissociative chemisorptions of molecular oxygen onto metal surface and subsequent electroreduction of oxides, we synthesize the carbon-supported nanometer silver/tungsten carbide hybrid (Ag-WC/C) using hydrothermal method and evaluate its electrochemical activity in pH-neutral phosphate buffer solution. Both the powder X-ray diffraction analysis and transmission electron microscopy observation suggest the formation of nanocrystalline structure of Ag (homogeneous particles of average 14 nm) and WC crystals that were uniformly dispersed on amorphous carbon support. Based on electrochemical measurements, the Ag-WC/C nanohybrids achieve catalysis of four-electron ORR with efficiency being comparable to commercial Pt/C catalyst. The promoted ORR activity should originate from the synergistic effect between WC and Ag nanoparticles. The inexpensive Ag-WC/C catalyst can produce a comparable magnitude of power density to commercial Pt/C catalyst in MFC. This study gives a demonstration of platinum-free high-efficiency and cost-effective ORR electrocatalyst for more sustainable electricity generation from biomass materials in MFC.