Mass Transport in Catalytic Pores of GDE-Based CO2 Electroreduction Systems

Abstract

Gas diffusion electrode (GDE)-based setups have shown promising performance for CO<sub>2</sub> electrocatalysis and further development of these systems will be important on the path to industrial feasibility. In this article, we model an effective catalyst pore within a GDE-based flow-cell to study the influence of the catalyst structure and operating conditions on the reaction environment for CO<sub>2</sub> electrocatalysis at practically relevant current densities. Using a generalized modified Poisson-Nernst-Planck (GMPNP) 3D model of the nanoporous catalyst layer, we show that the length of the catalyst pore as well as the boundary conditions at the gas-electrolyte and electrolyte-electrolyte interfaces across this length are highly influential parameters for determining the conditions within the catalyst pore. Pores with the same catalytic surface area can have very different reaction environments depending primarily on the pore length and not the pore radius. Properties such as electrolyte pH and buffer breakdown, ionic strength and CO<sub>2</sub> concentration are also highly-sensitive to the catalyst layer thickness, gas pressure, electrolyte flow rate and the flow-channel geometry. The applied potential impacts the concentration of ionic species in the pore, which in turn determines the solubility of CO<sub>2</sub> available for the reaction. Our results underline the need to understand and manage transport within GDE-based electrocatalysis systems as an essential means to control catalyst performance. Benchmarking of GDE-based electrocatalytic systems against their structural and operational parameters will be important for achieving improvements in performance that can be ultimately translated to large-scale operation.

Designing Copper‐Based Catalysts for Efficient Carbon Dioxide Electroreduction

“…The catalyst‐layer thickness may also affect the local concentration of cations within the catalyst pores, which are expected to play roles in the selectivity and activity. [ 193 ]…”

Dynamic Boundary Layer Simulation of Pulsed CO2 Electrolysis on a Copper Catalyst

“…These discrepancies in the CO 2 peaks can be attributed to the inability of the potentiostat to perform perfect step changes, the 1-s acquisition time of the differential electrochemical mass spectrometry, or the omission of double-layer formation from the model. 9 The time constant for the double-layer charging is approximately 6−30 ms, 21,33 and during that period, current would be dominated by double-layer charging as opposed to CO 2 R, mitigating the peaks simulated. To capture fully these effects, a molecularscale representation of the electrolyte double-layer is required, which is beyond the scope of the current work.…”

“…While the exact values for simulated C 2+ FE and total current density differ slightly from experiment, the trends are replicated to a reasonable level, and the discrepancies can be ascribed to errors in the fitted kinetic parameters or the experimental data collection capabilities. 9 Inspection of the reaction kinetics used in the model (see Section S2) 12,34 reveals how the partial current density for each product depends on the local pH and CO 2 concentration. Consistent with both experimental and theoretical studies, 4,5,11,12,35,36 the partial current densities for all CO 2 R products exhibit an approximately first order dependence on the local CO 2 concentration under the assumption of low surface coverage by all adsorbed species.…”

Mechanism for acetate formation in CO(2) reduction on Cu: Selectivity trends with pH and nanostructuring derive from mass transport

“…We also include a Sherwood relation to describe the convective mass transport encountered in a flow cell. It describes the diffusion of species from the bulk of the flowing electrolyte to the electrode surface [38][39][40] (see methods and SI Sec. 5).…”

“…The mass transport followed a hierarchical multiscale model where the transport within the GDE is solved via a 1-D model employing the electroneutral Nernst-Planck equation 37,60 and outside of the electrode described by effective mass transport relations. [38][39][40] The transport of CO was assumed solely from the gaseous side and solved analytically with a short diffusion layer of 350 nm, necessary to achieve the high current densities (see Fig. 4).…”