Boron-, Phosphorus-Doped Ordered Mesoporous Carbon Electrocatalysts for the Reduction of CO2 to Formic Acid
Authors: Sahin Nihat E. , Pescarmona Paolo P. 
Published: February 2020

Electrocatalytic reduction of CO2 stands out a promising approach towards carbon recycling since value-added chemicals and fuels can be produced at desired conditions. In recent decades, electrocatalytic reduction of CO2 has been extensively studied1-3, however development of effective materials capable of selectively reducing CO2 to formic acid (HCOOH) at low overpotentials is still on going. Metal-free electrocatalysts are the ideal candidates as next-generation, renewable materials that hold cost-effective and high-performance catalysts replacing precious metal catalysts. In particular, ordered mesoporous carbon channels as nano-reactor promote efficient diffusion path for CO2 access to the catalytic sites, improving the catalytic performance and Faradaic yield4. In this regard, we report here the synthesis of environmentally benign and active metal-free B- and P-doped ordered mesoporous carbon electrocatalysts and their performance towards CO2 reduction into formic acid in a batch electrolyzer. The B- and P- doped ordered mesoporous carbon (B-OMC and P-OMC) materials were prepared using SBA-15 silica as hard template and display high specific surface area (626 and 541 m2g-1), with narrow pore size distribution in the mesopore range (4.7 and 5.8 nm, respectively). A new two-step nanocasting strategy for obtaining highly effective ordered mesoporous carbons is also discussed5. Cyclic voltammetry measured under CO2 on the P-OMC electrode surface evidenced a broad peak centred at -1.20V (vs. Ag/AgCl sat. KCl) attributed to CO2 electroreduction (as confirmed by the absence of the peak if the voltammogram was measured under N2 (Fig.1). Further, the electrolysis of CO2 was investigated at controlled-potentials ranging between -1.40V and -1.80V (vs. Ag/AgCl) in a home-made two-compartment (H-type) cell. The Faradaic efficiency (F.E.) towards HCOOH was observed at -1.60 V (vs. Ag/AgCl), and reached at ca. 22% with an electrode loading of 2.38 mg cm-2 (inset Fig.1). Our recent efforts and findings, including development of nanostructured doped mesoporous carbon materials, and designing and constructing efficient electrochemical testing systems, prove that metal-free B- and P-doped ordered mesoporous carbon materials capable of selective reducing CO2 into formic acid, which is the target of the H2020 RECODE project in which this research is embedded.

Acknowledgements

This work was conducted in the framework of the RECODE project funded within the European Union`s Horizon 2020 Research and Innovation Programme under Grant Agreement No 768583. A postdoctoral fellowship to Dr. Nihat Şahin is gratefully acknowledged.

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Figure 1