High-resolution neutron imaging of salt precipitation and water transport in zero-gap CO2 electrolysis

Abstract

The electrochemical reduction of CO2 is a pivotal technology for the defossilization of the chemical industry. Although pilot-scale electrolyzers exist, water management and salt precipitation remain a major hurdle to long-term operation. In this work, we present high-resolution neutron imaging (6 μm) of a zero-gap CO2 electrolyzer to uncover water distribution and salt precipitation under application-relevant operating conditions (200 mA cm−2 at a cell voltage of 2.8 V with a Faraday efficiency for CO of 99%). Precipitated salts penetrating the cathode gas diffusion layer can be observed, which are believed to block the CO2 gas transport and are therefore the major cause for the commonly observed decay in Faraday efficiency. Neutron imaging further shows higher salt accumulation under the cathode channel of the flow field compared to the land.

Operandocharacterization of continuous flow CO2electrolyzers: current status and future prospects

“…[96][97][98][99] The aforementioned cell failure mechanisms are closely connected to the water management of the cell, thus their mitigation can be assisted by operando techniques that can give direct evidence on the relative humidity conditions or water content of the cell components. In this sense, radiographic analysis 78,91,100 or the incorporation of relative humidity and temperature sensors in the electrolyzers 73 are expected to contribute with novel insights. Additionally, methods that can locally measure the metal ion concentrations in the vicinity of the GDEs would also be highly desired.…”

“…These are focused on the membrane hydration, water distribution across the MEA and gas bubble formation in the electrolyte layers. 78,91,100,128,129 To maintain a high ionic conductance, therefore fast ion transport in CO2 electrolyzers, it is necessary for the ion exchange membrane to be in a well-hydrated state. 31 Recently neutron imaging was employed to directly quantify liquid water distribution across a MEA (Figure 11A).…”

“…Neutron/X-ray radiography 78,91,100,128,129 Water management Neutron/synchrotron facility Few seconds for X-ray few tenths of seconds for neutron mm -scale (x, y) Gas evolution Limited elemental information Precipitate formation Operando cell failure diagnostics Only minor cell modification needed Thermography 130 Local activity mapping One-to-one correlation between temperature change and activity has to be proved Depends on catalyst substrate, layer thickness, etc. Noninvasive probing to assess activity distribution a XAS: X-ray absorption spectroscopy, SECM: scanning electrochemical microscopy, AFM: atomic force microscopy, MS: mass spectrometry.…”

“…These are focused on the membrane hydration, water distribution across the MEA and gas bubble formation in the electrolyte layers. 78,91,100,128,129…”

“…High resolution neutron imaging (6 μm) was also performed in a zero-gap AEM electrolyzer (with Ag catalyst) to study water distribution and to observe salt precipitation at the cathode. 100 Up to 200 mA cm -2 the cathode became gradually dryer with increasing current density, because of the increased water consumption and electroosmotic drag from the cathode to the anode. (Figure 11B).…”