Abstract
Electrochemical CO2 reduction reaction (CO2RR) to liquid fuels is currently challenged by low product concentrations, as well as their mixture with traditional liquid electrolytes, such as KHCO3 solution. Here we report an all-solid-state electrochemical CO2RR system for continuous generation of high-purity and high-concentration formic acid vapors and solutions. The cathode and anode were separated by a porous solid electrolyte (PSE) layer, where electrochemically generated formate and proton were recombined to form molecular formic acid. The generated formic acid can be efficiently removed in the form of vapors via inert gas stream flowing through the PSE layer. Coupling with a high activity (formate partial current densities ~450 mA cm−2), selectivity (maximal Faradaic efficiency ~97%), and stability (100 hours) grain boundary-enriched bismuth catalyst, we demonstrated ultra-high concentrations of pure formic acid solutions (up to nearly 100 wt.%) condensed from generated vapors via flexible tuning of the carrier gas stream.
Highlights
Electrochemical CO2 reduction reaction (CO2RR) to liquid fuels is currently challenged by low product concentrations, as well as their mixture with traditional liquid electrolytes, such as KHCO3 solution
Our recent research has demonstrated the feasibility of solid electrolyte design for obtaining pure formic acid solutions[46], a few challenges still exist that impede its practical applications: the product concentration was limited due to the DI water flow stream in the solid electrolyte layer where a significant amount of water was present; the product generation rate was not sufficiently high for industrial applications; and it still involves the use of liquid electrolyte on the anode side for water oxidation
Gas diffusion layer (GDL) electrodes coated with CO2RR and hydrogen oxidation reaction (HOR) catalysts were used as cathode and anode to improve the mass transfer of both CO2 and H2
Summary
Electrochemical CO2 reduction reaction (CO2RR) to liquid fuels is currently challenged by low product concentrations, as well as their mixture with traditional liquid electrolytes, such as KHCO3 solution. Coupling with a high-activity (formate partial current densities > 440 mA cm−2), high-selectivity (maximal FE > 97%), and high-stability (100 h) grain boundary (GB)-enriched bismuth (Bi) catalyst, we demonstrated high concentrations of pure formic acid solutions (up to nearly 100 wt.%) condensed from its vapor by tuning the gas flow stream through the PSE layer, representing a superior catalytic performance compared with the existing systems (Fig. 1b and Supplementary Table 1).
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