Reaching the Fundamental Limitation in CO₂ Reduction to CO with Single Atom Catalysts

Abstract

The electrochemical CO2 reduction reaction (CO2RR) to value‐added chemicals with renewable electricity is a promising method to decarbonize parts of the chemical industry. Recently, single metal atoms in nitrogen‐doped carbon (MNC) have emerged as potential electrocatalysts for CO2RR to CO with high activity and faradaic efficiency, although the reaction limitation for CO2RR to CO is unclear. To understand the comparison of intrinsic activity of different MNCs, two catalysts are synthesized through a decoupled two‐step synthesis approach of high temperature pyrolysis and low temperature metalation (Fe or Ni). The highly meso‐porous structure results in the highest reported electrochemical active site utilization based on in situ nitrite stripping; up to 59±6% for NiNC. Ex situ X‐ray absorption spectroscopy (XAS) confirms the penta‐coordinated nature of the active sites. The catalysts are amongst the most active in the literature for CO2 reduction to CO. The density functional theory calculations (DFT) show that their binding to the reaction intermediates approximates to that of Au surfaces. However, it is found that the turnover frequencies (TOFs) of the most active catalysts for CO evolution converge, suggesting a fundamental ceiling to the catalytic rates.

Atomic metal coordinated to nitrogen-doped carbon electrocatalysts for proton exchange membrane fuel cells: a perspective on progress, pitfalls and prospectives

“…It can provide atomic surface chemical compositions of M-N-Cs, including light elements all the way up to hydrogen, with capabilities of depth profiling. ToF-SIMS can also distinguish single and dual metal atoms; 122,123 however, quantification using ToF-SIMS is highly challenging.…”

Sequential deposition of FeNC–Cu tandem CO2 reduction electrocatalysts towards the low overpotential production of C2+ alcohols

“…Electrochemical reduction of CO 2 (CO 2 RR) was carried out using an AUTOLAB PGSTAT302N potentiostat and a cell with 3-electrode configuration consisting of working, counter, and reference electrodes in a homemade gas diffusion cell. As recently reported by our group, the setup of a homemade cell includes a flow field, catholyte and anolyte compartment and an end plate [29]. For CO 2 RR measurements, a Pt/C electrode was employed as the counter electrode, leak-free Ag/AgCl as reference electrode [29], and the prepared electrocatalyst was coated onto hydrophobic carbon paper (carbon-based gas-diffusion, Sigracet 39 BB) and utilized as the working electrode with a geometrical area of 1 cm 2 .…”

“…As recently reported by our group, the setup of a homemade cell includes a flow field, catholyte and anolyte compartment and an end plate [29]. For CO 2 RR measurements, a Pt/C electrode was employed as the counter electrode, leak-free Ag/AgCl as reference electrode [29], and the prepared electrocatalyst was coated onto hydrophobic carbon paper (carbon-based gas-diffusion, Sigracet 39 BB) and utilized as the working electrode with a geometrical area of 1 cm 2 . Fumasep FAA 3-50 or Sustainion were used as an anion exchange membrane to separate the cathode and the anode, and both the cathodic and anodic chambers contained 1.5 ml of 0.5 M KHCO 3 , prepared by saturating a 0.5 M KOH solution with CO 2 (99.999%, BOC) for 30 mins to ensure that it was fully saturated with CO 2 .…”

“…By molecular tuning of Fe-porphyrins, they achieved a 22-fold increase of the TOF CO , which on the surface of Cu nanocubes with exposed (100) facets resulted in enhanced ethylene production. While these reports opened new avenues in the synthesis of hybrid electrocatalysts for high-added value chemicals production, the low stability and TOF CO of molecular electrocatalysts compared to that of Au or carbon-based single atom catalysts hinders the overall performance of the tandem system [29,30]. Additionally, the fine control of their spatial distribution remains a challenge.…”

“…To address this issues and facilitate effective spillover, we show a sequential spray coating method to synthesize tandem electrocatalysts where we employed our recently reported porous FeNC as the CO-producing electrocatalyst, which possesses record high electrochemical active site utilization (>50%) and one of the highest TOFco reported in literature to date [29,31]. To target the production of alcohols, we employed commercial shape-selected Cu nanoparticles with exposed Cu (111) facets, which have been shown to form ethanol rather than ethylene due to the favored CH X -CO coupling [22].…”