Electrochemical Reduction of CO2 on Au Electrocatalysts in a Zero-Gap, Half-Cell Gas Diffusion Electrode Setup: a Systematic Performance Evaluation and Comparison to a H-cell Setup

Abstract

Much research effort has been devoted to the development of effective catalysts for the electrochemical reduction of CO2 (CO2RR). For CO2RR, the most common catalyst screening method is performed in a H-cell configuration where the reactant CO2 gas is usually dissolved in an aqueous bicarbonate-based electrolyte. However, the low solubility of CO2 in aqueous solutions (∼35 mM at 298 K and 1 atm pressure) causes mass transport limitations in such setups.Based on H-cell measurements gold (Au) is one of the most selective catalysts for the CO2RR to CO. The preparation of small Au nanoparticles (NPs) based on conventional synthesis methods often requires the use of surfactants and capping agents such as polyvinylpyrrolidone (PVP).Here, we present a systematic evaluation of the performance of Au NPs for the CO2RR in our recently developed gas diffusion electrode (GDE) setup and compare the results to investigations in a conventional H-cell configuration. The GDE setup can be characterized as a zero gap, half-cell setup and supplies a continuous CO2 stream at the electrode−membrane electrolyte interface to circumvent CO2 mass transport limitations encountered in conventional H-cells. We investigate the influence of the catalyst loading as well as the influence of PVP. The results comparing the two screening methods show that the performance of the same catalyst can be substantially different in the different setups, which highlights the importance of having commercially relevant conditions for catalyst screening. In both setups, it is found that the presence of PVP favours the hydrogen evolution reaction (HER), however, in the GDE setup PVP is more detrimental for the performance than in conventional H-cells.

Optimizing the use of a “Zero-Gap” Gas Diffusion Electrode Setup for Electrochemical Reduction of CO2

“…In this study, we used surfactant free colloidal Au NPs with a size of ca. 8 nm, which were synthesized based on a laser ablation method 18 . After adding 13.3 mL of the Au NPs colloidal suspension (1 mg of Au) to the carbon suspension, the mixture was stirred for 10 min by means of the horn sonicator.…”

“…For the catalyst film preparation, the same vacuum filtration setup was used as reported in our previous work 18 . In this setup, a cylindrical reservoir with a cross-sectional area of 1.76 cm 2 was filled with 9.45 mL of the respective catalyst ink.…”

“…Both cathodic and anodic compartments were filled with 30 mL of 0.5 M potassium bicarbonate (KHCO3, ACS grade, Sigma-Aldrich, pH≈7.2) electrolyte. Despite the fact that glassy carbon is the most common catalyst substrate in H-cell configurations, to avoid a catalyst substrate effect, we used a GDL as the catalyst substrate in the H-cell setup as in our previous work 18 . This enables a fair comparison between the results of GDE setup and the H-cell setup.…”

“…In this study, we implemented our in-house developed GDE setup with a zero-gap half-cell design, to perform CO2 electrolysis on a standard gold (Au) electrocatalyst. The benefits of this zero-gap GDE setup have previously been demonstrated in a screening of Au nanoparticle (NP) catalysts to study the selectivity and activity towards the CO2RR under industrially relevant current densities 18 . Gálvez-Vázquez et al 19 showed that in long term applications, limitations due to bicarbonate precipitations influence the selectivity.…”