Prof. YAO Tao's team from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences, Prof. XIA Baoyu's team from Huazhong University of Science and Technology (HUST), and Dr. WANG Ziyun from the University of Auckland in New Zealand, developed a proton-exchange membrane (PEM) system that reduces carbon dioxide (CO₂) to formic acid at a catalyst derived from waste lead-acid batteries. The study was published in Nature. 

Developing various carbon-neutral technologies is crucial for addressing energy and environmental challenges. The CO₂ reduction reaction (CO₂RR) in a strong acid operated under a PEM system holds promise for scalable carbon conversion due to its ability to produce high-value chemicals and fuels with high current and long-term stability. 

In this study, the researchers achieved high CO₂RR activity with cathode recycled Pb (r-Pb) over a wide pH range, producing formic acid with a Faradaic efficiency exceeding 93% under 2.2 V voltage and continuous operation for 5200 hours at a current density of 600 mA cm^-2. 

To elucidate the true active structure of r-Pb catalysts in CO₂RR, they developed a self-designed membrane electrode CO₂RR in situ device suitable for X-ray absorption spectroscopy. Offline and in situ characterizations were conducted at BL12B X-ray magnetic circular dichroism (XMCD) at National Synchrotron Radiation Laboratory of USTC and beamline 1W1B (XAFS) at Beijing Synchrotron Radiation Facility. 

In situ X-ray absorption spectroscopy revealed a dynamic structural evolution of r-Pb from Pb/PbSO₄ to Pb/PbCO₃ under the reduction potential of CO₂RR. The coexistence of metallic Pb and PbCO₃ at the reduction potential was crucial for the high selectivity and activity of formic acid production. 

Further in situ infrared spectroscopy studies of CO₂RR were conducted based on the Hefei Light Source in situ infrared spectroscopy technology (BL01B). It was found that gaseous CO₂ on the surface of PbCO₃ undergoes surface activation before entering the PbCO₃ lattice where it is converted into HCOOH products. 

Combining the results with density functional theory calculations, the researchers unveiled the dynamic phase transition-induced lattice carbon activation and CO₂ conversion mechanism of r-Pb catalysts. 

This study signifies a step forward in understanding and advancing PEM CO₂ conversion technology.