Electrochemical carbon dioxide reduction reaction (CO2RR) enables conversion of greenhouse gas emissions into valuable chemical feedstocks under ambient temperature and pressure. Among all reduction products, formate has attracted extensive research interest for its simple reaction pathway, convenient liquid-state storage and broad downstream industrial applications.
However, in mainstream H-type electrolytic cells equipped with cation exchange membranes, cell voltage climbs continuously during operation. This escalation increases energy consumption, restricts formate concentration accumulation, and compromises long-term running stability — a critical bottleneck holding back industrial deployment. Traditional solutions such as periodic electrolyte refresh or enlarged electrolyte volume can only slow voltage growth temporarily, while severely diluting the formate product and fundamentally contradicting the goal of high-concentration production. The core mechanism behind the rapid voltage rise had not been systematically clarified until now.
A research team led by Prof. Xinmei Hou and Prof. Tao Yang from the Institute for Carbon Neutrality at the University of Science and Technology Beijing, in collaboration with researchers from Guangxi University and Central Research Institute of Building and Construction Co., Ltd. MCC, has uncovered the root cause of voltage escalation and developed a targeted, scalable solution.
Using a standard H-type cell with a proton exchange membrane, the team systematically tracked dynamic changes in ion concentration, conductivity and pH across both neutral KHCO3 and alkaline KOH electrolyte systems. They confirmed that potassium ions (K+), acting as the primary charge carriers, migrate unidirectionally from the anode compartment to the cathode compartment to maintain system electroneutrality. This migration creates a growing concentration gradient across the membrane, which generates diffusion potential that adds to the ohmic drop and drives the steady rise in overall cell voltage.
"For a long time, stability degradation was often attributed to catalyst or membrane aging. But our data clearly show that electrolyte composition change driven by cation migration is the key reason for rapid voltage increase within just a few hours," said Tao Yang, corresponding author of the study. "This mechanistic insight allowed us to address the problem from a completely new angle — electrolyte engineering rather than just catalyst optimization."
Building on this finding, the team proposed a "concentration-gradient" strategy: the anode chamber is filled with high-concentration (3.37 mol·L−1) electrolyte, while the cathode chamber uses low-concentration electrolyte (0.5 mol·L−1). The pre-set concentration difference generates a reverse diffusion potential that actively offsets the voltage increase caused by subsequent cation migration during electrolysis.
Experimental validation delivered remarkable results. In the KHCO₃ electrolyte system, the strategy kept cell voltage fluctuations within ±0.5 V for up to 30 hours of uninterrupted operation — approximately 3 to 4 times longer than conventional 1 mol·L-1 KHCO3 systems. Normalized formate productivity reached 310 μmol·cm-2·h-1·mA-1, a 200% increase compared to the reported average level. The KOH system achieved even better performance, with stable operation lasting about 33 hours and higher accumulated formate concentration.
The team further tested the strategy with NaHCO3 electrolyte and obtained consistent improvements, proving its broad applicability to all cation-based charge transport systems.
Looking forward, the research team notes that the concentration-gradient principle is not limited to formate production. It can potentially be extended to other CO2RR product systems where cation migration drives electrolyte evolution. The work offers a new design perspective for durable, energy-efficient CO2 electrolysis systems, and brings industrial-scale production of high-concentration carbon-based chemicals closer to reality.
This work was supported by the National Natural Science Foundation of China [NO. 52474319, 52450003, 52250091, U2341267]; the National Science Fund for Distinguished Young Scholars [NO. 52025041]; and the Fundamental Research Funds for the Central Universities of [NO. FRF-TP-20-02C2]. Furthermore, this project are supported by the Interdisciplinary Research Project for Young Teachers of USTB (Fundamental Research Funds for the Central Universities) [NO. FRF-IDRY-GD23-003]; Beijing Key Laboratory of High-Entropy Energy materials and Devices, Beijing Institute of Nanoenergy and Nanosystems [NO. GS2025MS022]; and Key Laboratory of Green Extraction & Efficient Utilization of Light Rare-Earth Resources (Inner Mongolia University of Science and Technology), Ministry of Education [NO. REKF26004].
About the Author
Dr. Tao Yang is a researcher and PhD supervisor at the Institute for Carbon Neutrality, University of Science and Technology Beijing, China, and a recipient of the National High-Level Personnel of Special Support Program-Outstanding Young Talent. His research interests focus on electrocatalytic CO2
