Although the Faraday efficiency (FE) for CO production of single-atom catalysts immobilized on nitrogen-doped carbon supports (M–N/C) for the CO2 electrocatalytic reduction reaction (CO2RR) is generally over 90%, M–N/C catalysts demonstrate a poor reaction current density, which is much worse than the current density at the industrial level. Herein, we first report a generalized amination strategy to significantly increase the current density for CO production of M–N/C catalysts (M = Ni, Fe, Zn). Among them, the aminated Ni single-atom catalyst achieves a remarkable CO partial current density of 450 mA cm−2 (a total current density over 500 mA cm−2) with a nearly 90% CO FE at a moderate overpotential of 0.89 V, and particularly CO FE can be maintained over 85% in a wide operating potential range from −0.5 V to −1.0 V. DFT calculations and experimental research demonstrate that the superior activity is attributed to enhanced adsorption energies of CO2* and COOH* intermediates caused by the regulation of the electronic structure of the aminated catalysts. This work provides an ingenious method for significantly increasing the current density at the industrially-relevant level of single-atom catalysts for the CO2RR.

Amination strategy to boost the CO2 electroreduction current density of M–N/C single-atom catalysts to the industrial application level

Transformation of biomass and CO2 into renewable value-added chemicals and fuels has been identified as a promising strategy to fulfill high energy demands, lower greenhouse gas emissions, and exploit under-utilized resources. Cost-effective and performance-efficient catalysts are of great importance to lowering the conversion cost of biomass and CO2. Significant progress has been made to advance the catalyst design for these processes, with metal catalysts playing a critical role in many involved catalytic reactions. Traditional nanoparticle-based metal catalysts still require improvement in metal utilization rates, stability, and selectivity tunability. Single-atom catalysts, which have maximum atomic efficiency and a uniform and tunable metal center, as well as an adjustable metal-support interaction, provide potential opportunities to boost catalyst efficiency and thermal stability. Their well-defined and uniform structure also provides advantages to fundamental studies for understanding of the intrinsic reaction mechanism and site requirement in biomass and CO2 conversion. Here, we summarize and highlight the recent advances in converting biomass and CO2 to renewable fuels and chemicals using single-atom catalysts. We discuss the design principles of single-atom catalysts and their potential applications to biomass and CO2 upgrading as well as the origins of catalytic activity. Moreover, we compare the catalytic efficiency of various catalysts reported thus to provide a fair assessment of these catalysts. Finally, perspectives are given on the interesting fields that may guide future studies.

Toward efficient single-atom catalysts for renewable fuels and chemicals production from biomass and CO2

We developed a tandem electrocatalyst for CO2 -to-CO conversion comprising the single Cu site co-coordinated with N and S anchored carbon matrix (Cu-S1 N3 ) and atomically dispersed Cu clusters (Cux ), denoted as Cu-S1 N3 /Cux . The as-prepared Cu-S1 N3 /Cux composite presents a 100 % Faradaic efficiency towards CO generation (FECO ) at -0.65 V vs. RHE and high FECO over 90 % from -0.55 to -0.75 V, outperforming the analogues with Cu-N4 (FECO only 54 % at -0.7 V) and Cu-S1 N3 (FECO 70 % at -0.7 V) configurations. The unsymmetrical Cu-S1 N3 atomic interface in the carbon basal plane possesses an optimized binding energy for the key intermediate *COOH compared with Cu-N4 site. At the same time, the adjacent Cux effectively promotes the protonation of *CO2 - by accelerating water dissociation and offering *H to the Cu-S1 N3 active sites. This work provides a tandem strategy for facilitating proton-coupled electron transfer over the atomic-level catalytic sites.

A Tandem Strategy for Enhancing Electrochemical CO 2 Reduction Activity of Single‐Atom Cu‐S 1 N 3 Catalysts via Integration with Cu Nanoclusters

The electrochemical CO2 reduction to high-value-added chemicals is one of the most promising and challenging research in the energy conversion field. An efficient ECR catalyst based on a Cu-based conductive metal-organic framework (Cu-DBC) is dedicated to producing CH4 with superior activity and selectivity, showing a Faradaic efficiency of CH4 as high as ~80% and a large current density of −203 mA cm−2 at −0.9 V vs. RHE. The further investigation based on theoretical calculations and experimental results indicates the Cu-DBC with oxygen-coordinated Cu sites exhibits higher selectivity and activity over the other two crystalline ECR catalysts with nitrogen-coordinated Cu sites due to the lower energy barriers of Cu-O4 sites during ECR process. This work unravels the strong dependence of ECR selectivity on the Cu site coordination environment in crystalline porous catalysts, and provides a platform for constructing highly selective ECR catalysts. Crystalline porous catalysts with single Cu sites are dedicated to exploring the dependence of CO2 electroreduction selectivity on the coordination environment of catalytic sites. The conductive MOF Cu-DBC with oxygen-coordinated Cu sites shows a high Faradaic efficiency ~80% of CO2-to-CH4.

Coordination environment dependent selectivity of single-site-Cu enriched crystalline porous catalysts in CO2 reduction to CH4.

Construction of atomically dispersed Cu-N4 sites via engineered coordination environment for high-efficient CO2 electroreduction

Scalable strategy to fabricate single Cu atoms coordinated carbons for efficient electroreduction of CO2 to CO

Solid-state synthesis of Cu nanoparticles embedded in carbon substrate for efficient electrochemical reduction of carbon dioxide to formic acid

Highly efficient, selective and reversible capture of sulfur dioxide by methylated-polyethylenimine supported on graphitic carbon nitride

Boosting electrochemical CO2 reduction on ternary heteroatoms-doped porous carbon

To achieve a selective catalytic reduction of nitrogen oxide (NOx) in a wide temperature range and avoid the secondary pollution of commercial catalysts, a new type of highly active catalyst Cu@ZIF-7 was synthesized. X-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy were performed to analyze the morphological characteristics of Cu@ZIF-7. The effects of Cu load capacity, impregnation time, impregnation temperature, catalyst dosage, and reaction temperature on NOx removal efficiency were also investigated. Cu@ZIF-7 maintained a NOx removal efficiency of >90% in a temperature range of 250–400 °C. Finally, the stability, sulfur, and water resistance of Cu@ZIF-7 were investigated, and the NOx conversion mechanism was inferred through in situ diffuse reflectance infrared Fourier transform spectroscopy and references. 

Xinyu Mao

Papers

Scalable strategy to fabricate single Cu atoms coordinated carbons for efficient electroreduction of CO2 to CO

Solid-state synthesis of Cu nanoparticles embedded in carbon substrate for efficient electrochemical reduction of carbon dioxide to formic acid

Highly efficient, selective and reversible capture of sulfur dioxide by methylated-polyethylenimine supported on graphitic carbon nitride

Boosting electrochemical CO2 reduction on ternary heteroatoms-doped porous carbon

NH3-selective catalytic reduction performance of a new type of Cu@ZIF-7 catalyst