Insights into Highly-Efficient CO₂ Electroreduction to CO on Supported Gold Nanoparticles in an Alkaline Gas-Phase Electrolyzer

Abstract

Electrochemical conversion of CO2 to fuels powered by renewable energy is an attractive technology for carbon emission reduction and renewable energy utilization elevation. Here, electrochemical reduction of CO2 to selectively produce CO using a homemade electrolyzer and Au nanocatalyst was investigated. Au nanoparticles were uniformly anchored on N-doped carbon to improve catalytic activity, and the C/N ratio and operating temperature were adjusted to elevate catalytic selectivity. The resulting Au catalyst exhibited a current efficiency for CO production higher than 90% in a wide full cell voltage range (1.8 ~3.0 V), a high mass activity of 900 A/gAu, and a total current density of 200 mA/cm2 under 3.0 V cell voltage at room temperature. A scale-up 3 × 3 cm CO2 electrolyzer was constructed and tested at 1 A, the current efficiency for CO production reached 93% but decreased within a few hours due to the potassium carbonate precipitation phenomenon at the cathode. The important influence of an unideal ion transport pathway during electrolysis on CO2 electrolyzer performance was revealed, and its stability can be greatly improved by using deionized water instead of KOH solution.

Strategies for the mitigation of salt precipitation in zero-gap CO2 electrolyzers producing CO

“…14,34 More details to the references can be found in Table 2. 5,8,12,16,[19][20][21]23,41,46,[54][55][56][57][58][59] Despite the lack of comprehensive data, general trends can be derived. Fig.…”

“…Fig. 8 shows the average CO 2 partial current density (a), the anolyte concentration (b) and the average cell voltage (c) in relation to the approximate amount of CO 2 that has been converted during the experiments of different works 5,8,12,16,[19][20][21]23,41,46,[54][55][56][57][58][59] normalized to the active cell area (also see Table 2). The amount of converted CO 2 was chosen, as it can be seen as a direct measure for stable performance without too much salt precipitation.…”

“…In general, salt precipitation occurs more rapidly with increasing electrolyte concentration, as the cation crossover from the anode side is also increased. Using pure water as electrolyte has been investigated 19,20 . Although it effectively inhibits precipitation, employing pure water has strong disadvantages for the cathode and anode reactions and membrane conductivity.…”

“…The operating temperature has an influence on many relevant properties like kinetics, ion conductivity, solubility, gas partial pressure, relative humidity and diffusivity. Zero-gap CO2 electrolyzers are often operated at low temperatures (<30 °C), as a reduced selectivity for CO was reported for elevated temperatures 19 . Nonetheless, this observation is not universally valid, as high CO partial current densities were demonstrated in cells operating at temperatures of up to 60 °C8 (see Table 2).…”

“…Using pure water as electrolyte has been investigated. 19,20 Although it effectively inhibits precipitation, employing pure water has strong disadvantages for the cathode and anode reactions and membrane conductivity. The neutral environment on the anode side leads to sluggish kinetics for the oxygen evolution reaction and requires scarce and expensive catalysts like iridium.…”