Electrochemical reactions in general, and the CO₂ reduction reaction (CO2RR) in particular, are commonly studied at room temperature. However, it is important to elucidate the effect of temperature on the product distribution and activity of CO2RR as practical electrolyzers will operate at elevated temperatures. We studied the effect of temperature on various metals. Gold as it is a relatively simple electrode material only producing CO and H₂, copper as it is an unique catalyst for CO2RR capable of producing a variety of products including multi-carbon products such as ethylene and propanol, and Ni because it is capable of producing longer hydrocarbon chains via a Fischer-Tropsch like mechanism. 

On Au, we show that increasing temperature leads to both an increase in activity and selectivity of the CO2RR towards CO. However, at higher temperatures mass transport limitations due to the lower CO₂ availability and higher local pH become more important. [1]

We show that at ambient pressures Cu has two distinct temperature regimes. From 18 up to ∿ 48 °C, C2+ products are produced with higher Faradaic efficiency, while methane and formic acid selectivity decreases, and hydrogen selectivity stays approximately constant. From 48 to 70 °C, we observe that hydrogen evolution dominates and the activity of CO2RR decreases. Moreover, the CO2RR products produced in this higher temperature range are mainly the C1 products CO and HCOOH. We show that CO surface coverage increases with temperature, which could explain the increase in C2+ products with temperature. Moreover, local pH and kinetics probably also play an important role in the first regime. The trends in the second regime appear most likely to be related to changes in the copper surface, while also a too high local pH will negatively influence the CO2RR. The decreasing CO₂ solubility with increasing temperature does not explain the trends observed. [2]

Ni shows increasing activity with temperature at ambient pressures, but the chain growth probability is intrinsically not much affected by the temperature. This means that the product distribution does not significantly change with temperature. However, we do observe that at higher temperatures, faster degradation takes place, probably due to coking of the catalyst.

Further experiments will be performed on both Cu and Ni at elevated pressures to study the effect of pressure and its combined effect with temperature. At higher pressures a larger temperature range can be studied. Moreover, the CO₂ solubility increases with increasing pressure, which makes it possible to study the temperature effect without the limitation of CO₂ bulk concentration.