Carbon dioxide (CO₂) electroreduction offers an attractive pathway for converting CO₂ to valuable fuels and chemicals. Despite the existence of some excellent electrocatalysts with superior selectivity for specific products, these reactions are conducted at low current densities ranging from several mA cm⁻² to tens of mA cm⁻², which are far from commercially desirable values. To extend the applications of CO₂ electroreduction technology to an industrial scale, long-term operations under high current densities (over 200 mA cm⁻²) are desirable. In this paper, we review recent major advances toward higher current density in CO₂ reduction, including: (1) innovations in electrocatalysts (engineering the morphology, modulating the electronic structure, increasing the active sites, etc.); (2) the design of electrolyzers (membrane electrode assemblies, flow cells, microchannel reactors, high-pressure cells, etc.); and (3) the influence of electrolytes (concentration, pH, anion and cation effects). Finally, we discuss the current challenges and perspectives for future development toward high current densities.

Due to CO₂ mass transfer limitation as well as the competition of hydrogen evolution reaction in electroreduction of CO₂ in the aqueous electrolyte, Zn-based electrodes normally exhibit unsatisfying selectivity for CO production, especially at high potentials. In this work, we introduced a zinc myristate (Zn [CH₃(CH₂)₁₂COO]₂) hydrophobic layer on the surface of zinc foam electrode by an electrodeposition method. The obtained hydrophobic zinc foam electrode showed a high Faradaic efficiency (FE) of 91.8% for CO at −1.9 V (vs. saturated calomel electrode, SCE), which was a remarkable improvement over zinc foam (FE_CO = 81.87%) at the same potentials. The high roughness of the hydrophobic layer has greatly increased the active surface area and CO₂ mass transfer performance by providing abundant gas-liquid-solid contacting area. This work shows adding a hydrophobic layer on the surface of the catalyst is an effective way to improve the electrochemical CO₂ reduction performance.

As a complex system involving three phases, the performance of CO2 electroreduction (CO2ER) is commonly constrained by mass transfer limitations originated from the low solubility of CO2 in aqueous electrolytes. Although some work has been carried out on mass transfer limitation, the underlying mechanism remains ambiguous. In this paper, a mass transfer model based on the Nernst-Planck equation was established to provide species concentration profiles within the catalyst layer and the internal effectiveness factor η was calculated to quantify the severity of mass transfer restrictions. The effects of catalyst layer thickness, diffusion layer thickness, and buffer concentration on CO2ER were evaluated based on η. Results show that the internal mass transfer is obvious in the catalyst layer. Increasing catalyst layer thickness only has a marginal benefit on current density — a thin catalyst layer (of about 15 μm) can give an excellent performance under an acceptable mass transfer limitation.

CO₂ electrochemical reduction is a promising way to convert CO₂ to valuable fuels and chemicals. This study presents a porous Cu@Zn foam catalyst with a tailored hydrophobic surface for enhanced CO₂ reduction. The catalyst is synthesized via a modified dynamic hydrogen bubble template method, incorporating polytetrafluoroethylene (PTFE) during electrodeposition to control wettability. This strategy creates a hydrophobic microenvironment that significantly increases the three-phase (gas–liquid–solid) contact area, promoting CO₂ mass transfer and suppressing the competing hydrogen evolution reaction. The optimized Cu@Zn-8PTFE catalyst achieves a CO Faraday efficiency (FE_CO) of 87.53% at −35 mA cm⁻², a 40% improvement over the unmodified Cu@Zn. Furthermore, it also exhibits excellent stability, maintaining FE_CO > 90% for 64 h at −15 mA cm⁻². While hydrophobic modification is beneficial, excess PTFE loading reduces performance by covering active sites and diminishing the three-phase interface. This work highlights the importance of controlling catalyst wettability to optimize the three-phase interface for enhanced CO₂ electroreduction.