Atomically Dispersed Indium Sites for Selective CO₂ Electroreduction to Formic Acid

Abstract

An atomically dispersed structure is attractive for electrochemically converting carbon dioxide (CO2) to fuels and feedstock due to its unique properties and activity. Most single-atom electrocatalysts are reported to reduce CO2 to carbon monoxide (CO). Herein, we develop atomically dispersed indium (In) on a nitrogen-doped carbon skeleton (In–N–C) as an efficient catalyst to produce formic acid/formate in aqueous media, reaching a turnover frequency as high as 26771 h–1 at −0.99 V relative to a reversible hydrogen electrode (RHE). Electrochemical measurements show that trace amounts of In loaded on the carbon matrix significantly improve the electrocatalytic behavior for the CO2 reduction reaction, outperforming conventional metallic In catalysts. Further experiments and density functional theory (DFT) calculations reveal that the formation of intermediate *OCHO on isolated In sites plays a pivotal role in the efficiency of the CO2-to-formate process, which has a lower energy barrier than that on metallic In.

Size‐Dependent Selectivity of Electrochemical CO2 Reduction on Converted In2O3 Nanocrystals

“…[39,40] It should be highlighted here that our r-15 nmnanocubes can achieve higher formate peak selectivity at more positive working potential compared to some other Inbased nanostructures (Figure S7). [16][17][18][19][20][21][22] Moreover, it is to our surprise that further reducing the particle size adversely affects the formate selectivity as observed for r-5 nm-NPs: it peaks at 83 % under À0.71 V, and then rapidly drops to < 60 % as the overpotential increases. The decline in formate selectivity is closely accompanied by the growth of H 2 selectivity, which reaches 35 % at À1.05 V, about three times higher than that of r-15 nm-nanocubes.…”

“…The large surface areas of r‐15 nm‐nanocubes induce a higher local pH which consequently suppresses HER and facilitates CO 2 RR to formate [39, 40] . It should be highlighted here that our r‐15 nm‐nanocubes can achieve higher formate peak selectivity at more positive working potential compared to some other In‐based nanostructures (Figure S7) [16–22] …”

“…[14] Since the pioneering works by Hori and co-workers in the 1990s, [15] great efforts have been invested on developing Inbased nanostructures with enlarged surface areas so as to promote their activities. [16][17][18][19][20][21][22] Most of them, unfortunately, have unsatisfactory formate selectivity: the peak selectivity is lower than 90 % and attainable only under highly cathodic working potential (< À0.8 V versus reversible hydrogen electrode or RHE). This leaves much room for further improvements.…”

Electrocatalysis enabled transformation of earth-abundant water, nitrogen and carbon dioxide for a sustainable future

“…Conversion of CO 2 as part of carbon capture and utilization (CCU) technologies has received increased interest in the past couple of decades, especially in view of favourable prospects related to positively impact the global climate change and renewable electricity production. 334,335 Researches in this field have mainly focused on fundamental and mechanistic conversion of CO 2 to valuable fuels and chemicals through a variety of technologies including biochemical 336 , thermochemical 337 , photochemical 338 and electrochemical 339 reduction of CO 2 . Among these technologies, electrocatalytic CO 2 reduction reaction (CRR) has attracted greater attention by virtue of its mild operation condition and great potential to scale up.…”

“…413 And FeN 4 sites in Fe-N-C catalysts were also obtained from the ZIF-8 which reached 25 mA/cm 2 at 0.8V (vs. RHE) and FE was above 90% for CO in a wide potential. 414 339 Furthermore, to enrich the distribution of active sites, enabling a large catalyst surface area can feature catalytic active centers to improve the CRR performance. On this account, a myriad of 2D materials including nanosheets and nanofilms of metal, metal oxides and chalcogenides have portrayed good CRR activity and selectivity.…”