A team of NETL and University of Pittsburgh researchers has developed a record-setting catalyst that electrochemically converts carbon dioxide (CO₂) and water into formic acid, which can be used as a hydrogen carrier in the new clean energy economy.

“We carefully optimized the catalyst formulation to maximize performance, and the demonstrated activity and product selectivity are among the highest reported in the literature,” said NETL’s lead author Thuy Duong Nguyen Phan on a freely-available, open access article detailing the research in the high-impact-factor journal Applied Catalysis B: Environmental.

Increasing catalyst selectivity is crucial in chemical reactions because higher selectivity means that the catalyst will enable maximized yield of the converted material — in this case, formic acid. Electrochemical CO₂ reduction (CO₂R) into renewable chemicals and fuels, such as formic acid, carbon monoxide, methane or ethylene, is a promising pathway toward recycling carbon emissions.

“Formic acid is a versatile liquid product that has potential uses in fuel cells, agricultural, chemical and pharmaceutical applications,” said NETL co-authors James Ellis and Douglas Kauffman. “Additionally, and more importantly for our nation’s decarbonization goals, formic acid produced via CO₂R has been identified as an economically viable green hydrogen carrier, which means that the hydrogen is stored in another form and then separated out when needed. The liquid state of formic acid reduces the challenges associated with compressing, transporting and storing gaseous hydrogen.”

Deliberately adding sulfur into tin-based catalysts, known as doping, has been shown to improve CO₂R activity and selectivity; however, the precise relationship between sulfur-dopant levels and catalyst performance remains largely unexplored from an experimental standpoint.

In this work, the NETL-led team sought to close that knowledge gap and experimentally quantified the composition-dependent role of sulfur dopants, demonstrating that its beneficial influence on CO₂ conversion only occurs over a very narrow composition range.

“We investigated various concentrations of sulfur dopants between approximately 1 and 11%,” Nguyen Phan said. “Surprisingly it was at the lower end, about 1.4% sulfur content, that we saw the most promising results — a five-fold improvement in conversion performance compared to an undoped catalyst. This shows that a little bit of sulfur dopant goes a long way to improving catalyst performance — something no one has shown before!”

The research will help provide further insight into the design of high-performance CO₂R electrocatalyst, which will be needed as the nation shifts to a clean energy economy enabled by hydrogen.

NETL is a U.S. Department of Energy national laboratory that drives innovation and delivers technological solutions for an environmentally sustainable and prosperous energy future. By its world-class talent and research facilities, NETL is ensuring affordable, abundant and reliable energy that drives a robust economy and national security, while developing technologies to manage carbon across the full life cycle, enabling environmental sustainability for all Americans.