RESUMEN
The electrochemical reductive valorization of CO2, referred to as the CO2RR, is an emerging approach for the conversion of CO2-containing feeds into valuable carbonaceous fuels and chemicals, with potential contributions to carbon capture and use (CCU) for reducing greenhouse gas emissions. Copper surfaces and graphene-embedded, N-coordinated single metal atom (MNC) catalysts exhibit distinctive reactivity, attracting attention as efficient electrocatalysts for CO2RR. This review offers a comparative analysis of CO2RR on copper surfaces and MNC catalysts, highlighting their unique characteristics in terms of CO2 activation, C1/C2(+) product formation, and the competing hydrogen evolution pathway. The assessment underscores the significance of understanding structure-activity relationships to optimize catalyst design for efficient and selective CO2RR. Examining detailed reaction mechanisms and structure-selectivity patterns, the analysis explores recent insights into changes in the chemical catalyst states, atomic motif rearrangements, and fractal agglomeration, providing essential kinetic information from advanced in/ex situ microscopy/spectroscopy techniques. At the end, this review addresses future challenges and solutions related to today's disconnect between our current molecular understanding of structure-activity-selectivity relations in CO2RR and the relevant factors controlling the performance of CO2 electrolyzers over longer times, with larger electrode sizes, and at higher current densities.
RESUMEN
Nonconductive porous polymer substrates, such as PTFE, have been pivotal in the fabrication of stable and high-performing gas diffusion electrodes (GDEs) for the reduction of CO2/CO in small scale electrolyzers; however, the scale-up of polymer-based GDEs without performance penalties to technologically more relevant electrode sizes has remained elusive. This work reports on a new current collector concept that enables the scale-up of PTFE-based GDEs from 5 to 100 cm2 and beyond. The present approach builds on a multifunctional current collector concept that enables multipoint front-contacting of thin catalyst coatings, which mitigates performance losses even for high resistivity cathodes. Our improved current collector design concomitantly incorporates a flow-field functionality in a monopolar plate configuration, keeping electrolyte gaps small for increased performance. Experiments with 100 cm2 cathodes were conducted in a one-gap alkaline AEM and acid CEM system. Our design represents an important step forward in the development of larger-size CO2 electrolyzers.
RESUMEN
Coupled tandem electrolyzer concepts have been predicted to offer kinetic benefits to sluggish catalytic reactions thanks to their flexibility of reaction environments in each cell. Here we design, assemble, test, and analyze the first complete low-temperature, neutral-pH, cathode precious metal-free tandem CO2 electrolyzer cell chain. The tandem system couples an Ag-free CO2-to-CO2/CO electrolyzer (cell-1) to a CO2/CO-to-C2+ product electrolyzer (cell-2). Cell-1 and cell-2 incorporate selective Ni-N-C-based and Cu-based Gas Diffusion Cathodes, respectively, and operate at sustainable neutral pH conditions. Using our tandem cell system, we report strongly enhanced rates for the production of ethylene (by 50%) and alcohols (by 100%) and a sharply increased C2+ energy efficiency (by 100%) at current densities of up to 700 mA cm-2 compared to the single CO2-to-C2+ electrolyzer cell system approach. This study demonstrates that coupled tandem electrolyzer cell systems can offer kinetic and practical energetic benefits over single-cell designs for the production of value-added C2+ chemicals and fuels directly from CO2 feeds without intermediate separation or purification.