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

The lack of a robust and standardized experimental test bed to investigate the performance of catalyst materials for the electrochemical CO2 reduction reaction (ECO2RR) is one of the major challenges in this field of research. To best reproduce and mimic commercially relevant conditions for catalyst screening and testing, gas diffusion electrode (GDE) setups attract a rising attention as an alternative to conventional aqueous-based setups such as the H-cell configuration. In particular a zero-gap design shows promising features for upscaling to the commercial scale. In this study, we develop further our recently introduced zero-gap GDE setup for the CO2RR using an Au electrocatalyst as model system and identify/report the key experimental parameters to control in the catalyst layer preparation in order to optimize the activity and selectivity of the catalyst.

Operando XAS of a Bifunctional Gas Diffusion Electrode for Zn-Air Batteries under Realistic Application Conditions

In this study, operando X-ray absorption spectroscopy (XAS) measurements were carried out on a newly developed O2 bi-functional gas diffusion electrode (GDE) for rechargeable Zn-air batteries, consisting of a mixture of α-MnO2 and carbon black. The architecture and composition of the GDE, as well as the electrochemical cell, were designed to achieve optimum edge-jumps and signal-to-noise ratio in the absorption spectra for the Mn K-edge at current densities that are relevant for practical conditions. Herein, we reported the chemical changes that occur on the MnO2 component when the GDE is tested under normal operating conditions, during both battery discharge (ORR) and charge (OER), on the background of more critical conditions that simulate oxygen starvation in a flooded electrode.

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

Based on H-cell measurements, gold (Au) is one of the most selective catalysts for the CO2 reduction reaction (CO2RR) to CO. To ensure a high dispersion, typically Au small nanoparticles (NPs) are used as catalyst. However, the preparation of small Au NPs based on conventional synthesis methods often requires the use of surfactants such as polyvinylpyrrolidone (PVP). Here, we present a systematic evaluation of the performance of laser-generated, surfactant-free Au NPs for the CO2RR in a gas diffusion electrode (GDE) setup and compare the results to investigations in an H-cell configuration. The GDE setup supplies a continuous CO2 stream at the electrode−electrolyte interface to circumvent CO2 mass transport limitations encountered in conventional H-cells. We investigate the influence of the catalyst loading and the effect of PVP. Comparing the two screening methods, i.e. GDE and H-cell measurements, it is shown that the performance of the same catalyst can be substantially different in the two environments. In the GDE setup without liquid electrolyte-catalyst interface a higher reaction rate, but lower faradaic efficiendy is determined. Independent of the setup, the presence of PVP favours the hydrogen evolution reaction (HER), however, in the GDE setup PVP is more detrimental for the performance than in the H-cell.

On the electro-oxidation of small organic molecules: towards a fuel cell catalyst testing platform

The electrocatalytic oxidation of small organic compounds such as methanol or formic acid has been the subject of numerous investigations in the last decades. The motivation for these studies is often their use as fuel in so-called direct methanol or direct formic acid fuel cells, promising alternatives to hydrogen-fueled proton exchange membrane fuel cells. The fundamental research spans from screening studies to identify the best performing catalyst materials to detailed mechanistic investigations of the reaction pathway. These investigations are commonly performed in standard three electrode electrochemical cells with a liquid supporting electrolyte to which the methanol or formic acid is added. In fuel cell devices, however, no liquid electrolyte will be present, instead membrane electrolytes are used. The question therefore arises, to which extend results from conventional electrochemical cells can be extrapolated to conditions found in fuel cells. We previously developed a gas diffusion electrode setup to mimic “real-life” reaction conditions and study electrocatalysts for oxygen gas reduction or water splitting. It is here demonstrated that the setup is also suitable to investigate the properties of catalysts for the electro-oxidation of small organic molecules. Using the gas diffusion electrode setup, it is seen that employing a catalyst - membrane electrolyte interface as compared to conventional electrochemical cells can lead to significantly different catalyst performances. Therefore, it is recommended to implement gas diffusion electrode setups for the investigation of the electro-oxidation of small organic molecules.

The Gas diffusion electrode setup as a testing platform for evaluating fuel cell catalysts: a comparative RDE-GDE study

Gas diffusion electrode (GDE) setups have been recently introduced as a new experimental approach to test the performance of fuel cell catalysts. As compared to the state-of-the-art in fundamental research, i.e., rotating disk electrode (RDE) measurements, GDE measurements offer several advantages. Most importantly mass transport limitations, inherent to RDE measurements are avoided. In a GDE setup the reactant, e.g., oxygen gas, is not dissolved into a liquid electrolyte but distributed through a gas diffusion layer (GDL), as it is actually the case in fuel cells. Consequently, much higher current densities can be achieved, and the catalysts can be studied in a wider and more relevant potential range. Furthermore, direct contact to a liquid electrolyte can be avoided and elevated temperatures can be employed in a straight-forward manner. However, the use of GDE setups also comes with some challenges. The determined performance is not strictly related to the catalyst itself (intrinsic activity), but also to the quality of the catalyst film preparation. Therefore, it might be even more important than in RDE testing to develop standardized procedures to prepare catalysts inks and films that can be reproduced effortlessly in research laboratories for fundamental and applied experimentation. To develop such standardized testing protocols, we present a comparative RDE – GDE study, where we investigate several commercial standard Pt/C fuel cell catalysts with respect to the oxygen reduction reaction (ORR). The study highlights the strengths of the GDE approach as an intermediate “testing step” between RDE and membrane electrode assembly (MEA) tests when developing new fuel catalysts.