(Invited) Development of Hybrid Structured Materials for Electrocatalytic, Bioelectrocatalytic and Photoelectrochemical Reduction of Carbon Dioxide
Authors: Kulesza Pawel J , Wadas Anna , Seta Ewelina , Szaniawska Ewelina , Bienkowski Krzysztof , Solarska Renata , Rutkowska Iwona Agnieszka 
Published: February 2020

There has been growing interest in the electrochemical reduction of carbon dioxide, a potent greenhouse gas and a contributor to global climate change. Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large overpotentials. To produce highly efficient and selective electrocatalysts, the transition-metal-based molecular materials are often considered. It is believed that, during electroreduction, the rate limiting step is the protonation of the adsorbed CO product to form the CHO adsorbate.
To optimize the hydrogenation-type electrocatalytic approach, we have proposed to utilize nanostructured metallic centers (e.g. Pd, Pt or Ru) in a form of highly dispersed and reactive nanoparticles generated within supramolecular network of distinct nitrogen, sulfur or oxygen-coordination complexes. Reduction of carbon dioxide begins now at less negative potentials and is accompanied by significant enhancement of the reduction current densities. Among important issues are the mutual completion between hydrogen evolution and carbon dioxide reduction and specific interactions between coordinating centers and metallic sites.
We have also explored the ability of biofilms to form hydro-gel-type aggregates of microorganisms attached to various surfaces including those of carbon electrode materials. Biofilms are able to transfer electrons to and from electrodes, and they can act in a manner analogous to redox or conducting polymer films on electrodes. Here we have explored a biofilm formed by a strain of Yersinia enterocolitica as active bioelectrocatalytic support; it is characterized by long-term stability over wide ranges of pH (4-10) and temperatures (0-40°C). Upon incorporation of various noble metal nanostructures and/or conducting polymer ultra-thin films, a highly reactive and selective system toward CO2-reduction is obtained.
Another possibility to enhance electroreduction of carbon dioxide is to explore direct transformation of solar energy to chemical energy using transition metal oxide semiconductor materials. We show here that, by intentional and controlled combination of metal oxide semiconductors, we have been able to drive effectively photoelectrochemical reduction of carbon dioxide. The combination of titanium (IV) oxide and copper (I) oxide has been explored toward the reduction of CO2 before and after illumination. Application of the hybrid system composed of both oxides has resulted in high current densities originating from photoelectrochemical reduction of carbon dioxide mostly to methanol, as demonstrated upon identification of final products using conventional and mass-spectrometry-assisted gas chromatography. A role of TiO2 is not only stabilizing: the oxide is also expected to prevent the recombination of charge carriers. Bacterial-biofilm-enhanced photoelectrochemical interfaces for improved reduction of carbon dioxide will also be considered.