The global population currently uses energy at a rate of nearly 16 terawatts, of which more than 80 percent is supplied by fossil fuel combustion. We are pursuing catalysts that use renewable energy sources to power the synthesis of carbon-containing fuels from H2O and CO2. Specifically, we are developing electrode materials that convert CO2 and H2O into fuel when supplied with electricity, a process known as electrochemical CO2 reduction. Electrolyzers containing these electrodes could be powered by photovoltaics or windmills. Researchers have identified several metal electrodes that are capable of catalyzing CO2 reduction, but unfortunately none are efficient or stable enough for use in an electrolyzer.
Supported by the Precourt seed grant, we have developed two novel catalysts that open new avenues of investigation and bring us much closer to this technological goal. The first catalyst is a composite material composed of tin metal and tin oxide particles in intimate contact with one another. Whereas tin metal alone exhibits almost no CO2 reduction activity, the composite material reduces CO2 to CO and HCO2H at an efficiency that is close to what would be necessary for practical electrolysis. The second catalyst consists of copper nanoparticles (particles with a diameter of approximately 15 nm) produced by the reduction of copper oxide. Remarkably, when a very thick copper oxide film is reduced to copper nanoparticles, these particles are extremely active for CO2 reduction catalysis.
Our best copper nanoparticle catalysts to date reduce CO2 to CO and formic acid (HCO2H) with greater efficiency than has ever been reported in the CO2 reduction literature. We are very excited about determining the detailed structural features of the copper nanoparticles that account for their high activity (ordinary copper is a very inefficient CO2 reduction catalyst) and further improving this catalyst for possible evaluation in an electrolyzer. One major challenge on the immediate horizon is to improve the selectivity for formic acid vs CO formation. We think that renewably-produced formic could be a fuel used on a very large scale in fuel cells or as a liquid H2 carrier.