From CO₂ to Formic Acid Fuel Cells

Abstract

Formic acid is a liquid, safe, and energy-dense carrier for fuel cells. Above all, it can be sustainably produced from the electroreduction of CO2. The formic acid market is currently saturated, and it requires alternative applications to justify additional production capacity. Fuel cell technologies offer a chance to expand it, while creating an opportunity for sustainability in the energy sector. Formic acid-based fuel cells represent a promising energy supply system in terms of high theoretical open-circuit voltage (1.48 V). Compared to common fuel cells running on H2 (e.g., proton-exchange membrane fuel cells), formic acid has a lower storage cost and is safer. This review focuses on the sustainable production of formic acid from CO2 and on the detailed analysis of commercial examples of formic acid-based fuel cells, in particular direct formic acid fuel cell stacks. Designs described in the literature are mostly at the laboratory scale, still, with 301 W as the maximum power output achieved. These case studies are fundamental for the scale-up; however, additional efforts are required to solve crossover and increase performance.

Recent advances in electrocatalysts, mechanism, and cell architecture for direct formic acid fuel cells

“…Ma et al recently reviewed the different DFAFC stack examples for future development and commercialization as part of their review of the sustainable production of FA from CO 2 and its implementation. The stacks reported in the literature had several MEAs ranging from 2 to 35, delivering power outputs ranging from 0.4 to 301 W. They stressed the need to tackle fuel crossover issues at the high FA concentrations that are necessary for commercial applications (Z. Ma, Legrand, et al, 2020). Problems pertaining to mass transfer limitations, poor distribution of fuel, efficient product gas removal, and stability of components also need to be addressed.…”

Mechanism of CO2 hydrogenation over a Zr1–Cu single-atom catalyst

“…Reduction and conversion of CO 2 into small organic molecules or hydrocarbons can not only alleviate global warming caused by the greenhouse effect, but also provide a new way to meet future energy demand. 1 Hydrogenation products of CO 2 mainly include methanol (CH 3 OH), 2–5 methane (CH 4 ), 6,7 formic acid (HCOOH), 8–10 dimethyl ether (CH 3 OCH 3 ), 11–13 and CO. 14–18 CO is used to produce liquid fuels such as olefin and polyol through the Fischer–Tropsch (FT) process and other mature processes. 19–24 Methanol is a liquid solar fuel, and it is highly significant to realize the hydrogenation of CO 2 to methanol.…”

Benchmarking Catalysts for Formic Acid/Formate Electrooxidation

“…Hydrogen is a gas at ambient conditions and must be stored under high pressure or liquefied at low temperatures. As such, growing interest has been paid towards the direct formic acid/formate (FA) electrooxidiation reaction, which can be used as a low-carbon energy vector/hydrogen carrier for exploitation in carbon-neutral fuel cycles [ 6 , 7 , 8 , 9 , 10 , 11 ]. FA fuel cycles are carbon neutral because FA can be directly produced by electrochemical CO 2 reduction driven by renewable energy sources.…”

“…Moreover, FA is safer than hydrogen because it can be stored and transported as a salt or dissolved in water. Finally, FA fuel cells (FAFCs) have higher theoretical cell voltage (1.45 V using oxygen as oxidant, compared to 1.23 V vs. fuel cells based on H 2 ) and lower crossover limitations than those based on other liquid fuels like methanol (1.23 V) and ethanol (1.14 V), theoretically resulting in higher power density [ 6 , 13 ].…”

“…The complexity of the FA electroxidation reaction (FAEOR) results in sluggish kinetics and hinders fuel cell power density. Indeed, despite being investigated since the early 1960s of the twentieth century [ 29 , 30 ], the lack of electrocatalysts with suitable catalytic activity and durability is still the main concern limiting the competitiveness of FAFC and hinders its large-scale use [ 6 , 13 , 31 , 32 ]. Similar to other types of low-temperature fuel cells, FAFC are still dependent on PGM catalysts, in particular Pd and Pt.…”