The development of an artificial photosynthesis system that converts CO₂ into a kind of chemical energy with high efficiency is one of the major issues to solve energy and environmental problems. 

Electromicrobial conversion of CO₂ is a promising alternative to the direct transfer of CO₂ into biomass by using bacteria. The bacteria consume H₂ and CO₂ for living. The efficiency of such a hybrid system strongly depends on the electrocatalyst used for water-splitting to produce H₂. 

To achieve high conversion efficiency, the electrocatalyst must be stable, with low overpotential and high biocompatibility during the electrolysis. 

A research team led by Prof. Zhang Guangjin from the Institute of Process Engineering (IPE) of the Chinese Academy of Sciences evidenced that a mixed noble metal free Co/Cu-containing polyoxometalate/Carbon Cloth (Cu₆Co₇/CC) hybrid possesses excellent activity, stability and biocompatibility as a water splitting electrocatalyst at neutral pH. 

The long term stability of the activated noble metal-free electrodes together with their good biocompatibility-a negligible amount of hydrogen peroxide being produced during the electrolysis process-made it suitable for applications in biosynthetic systems. 

CO₂ conversion with bacteria and the Cu₆Co₇ catalyst as both anode and cathode materials has been tested. The hydrogen produced at the cathode was the sole source of biological reducing agents.

The growth of the bacteria and the accumulation of biomass were monitored by UV-vis spectroscopy. It can be obtained by calculation that the overall solar-to-biomass efficiency of this hydride system can reach 10%, which is nearly 10 times higher than the performance of natural plants.  

Their study entitled "An overall water-splitting polyoxometalate catalyst for the electromicrobial conversion of CO₂ in neutral water" was published in Journal of Materials Chemistry A. 

This work was supported by the National Natural Science Foundation of China and Youth Innovation Promotion Association of CAS. 

Schematic illustration of the bioelectrochemical system for CO₂ fixation. (Image by ZHANG Guangjin et al.)