Novel strategy boosts CO₂ electroreduction efficiency and durability

The Yabu Laboratory at the Tohoku University Advanced Institute for Materials Research (WPI-AIMR) has recently demonstrated a novel strategy that yields a highly efficient electrocatalyst. Using cobalt tetraazaphthalocyanine (CoTAP), this approach achieved a mass activity 3.77 times higher than that of pristine CoPc.

Their findings, published in the journal Small, represent an advancement in efficiency and cost-effectiveness for catalysts that can transform harmful carbon dioxide (CO₂) into a much more convenient form.

CO₂ emission reduction is one of the most urgent global challenges we face today. One potential solution is the electrochemical reduction of CO₂ (ECR), which converts CO₂ into valuable feedstocks such as carbon monoxide (CO). ECR uses a carbon recycling method powered by renewable energy, making it a promising option to fight climate change. However, this process requires catalysts with high selectivity. The catalysts that are currently used are made from noble metals (like gold and silver) or other materials that suffer from high costs and limited selectivity.

To address these issues, the Yabu Laboratory previously developed two strategies: direct crystallization of M-Pcs (inexpensive blue pigments), and crystallization on carbon materials. These methods achieved both high CO₂-to-CO efficiency and good durability. Nevertheless, further improvements in activity, durability, and mass activity―the ability to maintain high catalytic performance with minimal catalyst loading―are still required.

In this study, the Yabu team advanced the second strategy by applying it to pyridinic-N modified CoTAP, which has attracted attention as a catalyst for fuel cells and metal-air batteries. CoTAP is a derivative of CoPc in which the four benzene rings are replaced with pyridine rings. This modification is expected to strengthen electrostatic interactions with CO₂ molecules and enhance adsorption at catalytic sites.

The team crystallized both pristine CoPc and CoTAP on the surface of the conductive carbon material Ketjen Black (KB), coated them onto gas diffusion electrodes, and performed ECR testing. CoTAP electrodes achieved a Faradaic efficiency above 98% for CO₂-to-CO conversion, enabled high-rate electrolysis at current densities over 1 A/cm², and maintained durability for 112 hours at 150 mA/cm².

CoTAP also exhibited 3.77 times higher mass activity than CoPc, demonstrating superior performance with less catalyst. The exceptional performance of CoTAP is attributed to its lower electrical resistance and higher conductivity relative to CoPc crystals.

“Compared with previously reported M-Pc-based catalysts, CoTAP delivered outstanding results across all metrics, including maximum current density, turnover frequency, durability, mass activity, and Faradaic efficiency,” remarks Hiroshi Yabu (WPI-AIMR).

Importantly, this research provides a pathway to reduce reliance on expensive noble metals, lower the energy cost of CO₂ utilization, and accelerate the development of next-generation carbon capture and utilization technologies. This breakthrough carves a practical path towards transforming waste CO₂ into valuable resources, and helping society transition toward a cleaner and more sustainable future.