Water formation at the cathode and sodium recovery using Microbial Fuel Cells (MFCs)

• A range of Pt-free cathodes generate electrical current with simultaneous catholyte production.
• Catholyte formation in situ directly related to MFC performance.
• The synthesised catholyte contains up to 9% sodium salts.
• Catholyte accumulation enhances remediation and recovery of elements.
• First demonstration of MFC as carbon capture technology with wet scrubbing cathode.

Microbial Fuel Cells (MFCs) utilise biodegradable carbon compounds in organic waste to generate electric current. The aim of this work was to enhance MFC performance by using low cost and catalyst (platinum)-free cathode materials. The results showed that the range of Pt-free cathodes including activated carbon, plain carbon fibre veil with and without microporous layer (MPL) in two-chamber MFCs generated power with simultaneous catholyte generation in the cathode chamber. This is the first time to report a clear catholyte formation on the cathode half cell, which was directly related to MFC power performance. The importance of this phenomenon may be attributed to the oxygen reduction reaction, water diffusion and electroosmotic drag. The synthesised catholyte in situ on the open-to-air cathode appeared to be sodium salts (9% w/v concentration), which was recovered from the anolyte feedstock containing sludge and sodium acetate. An overlooked benefit of catholyte formation and accumulation contributes greatly to the overall wastewater treatment, water recovery, bioremediation of salts and carbon capture.