CO₂ Overall Splitting by a Bifunctional Metal‐Free Electrocatalyst

Abstract

Photo/electrochemical CO splitting is impeded by the low cost-effective catalysts for key reactions: CO reduction (CDRR) and water oxidation. A porous silicon and nitrogen co-doped carbon (SiNC) nanomaterial by a facile pyrolyzation was developed as a metal-free bifunctional electrocatalyst. CO -to-CO and oxygen evolution (OER) partial current density under neutral conditions were enhanced by two orders of magnitude in the Tafel regime on SiNC relative to single-doped comparisons beyond their specific area gap. The photovoltaic-driven CO splitting device with SiNC electrodes imitating photosynthesis yielded an overall solar-to-chemical efficiency of advanced 12.5 % (by multiplying energy efficiency of CO splitting cell and photovoltaic device) at only 650 mV overpotential. Mechanism studies suggested the elastic electron structure of -Si(O)-C-N- unit in SiNC as the highly active site for CDRR and OER simultaneously by lowering the free energy of CDRR and OER intermediates adsorption.

Single‐Atom Electrocatalysts from Multivariate Metal–Organic Frameworks for Highly Selective Reduction of CO2 at Low Pressures

“…[27][28][29] In addition to the active site identification, another critical issue in CO 2 RR is the energy-consuming capture and purification process of CO 2 .Specifically speaking,toachieve high selectivity,t he currently reported CO 2 RR are generally performed in pure CO 2 . [30][31][32][33][34][35][36][37][38][39][40][41][42] However,t he actual concentration of CO 2 feedstock available from industrial processes such as coal power plant (5-15 %CO 2 )and steel/petrochemical industry (14-33 %C O 2 )i sr elatively low. [43][44][45] Given the thermodynamic stability of the C = Obond ( % 806 kJ mol À1 )of CO 2 and its limited solubility in aqueous solution, low CO 2 concentration will significantly affect the activity,setting great barriers for the direct CO 2 utilization.…”

Electrochemical Carbon Dioxide Splitting

“…There are also some reported electrolyzers equipped with proton exchange membrane, such as Nafion membrane, which provides the channel for protons transfer (Figure c). In this case, both of catholyte and anolyte were neutral solutions commonly, which promotes a significant anodic catalyst requirement for neutral water oxidation ,,. In the three‐compartment electrolyzer, catholyte can also be basic solution, which can suppress competitive HER and avoid the side reaction between CO 2 and hydroxyl that would occur in H‐type electrolyzer.…”

Metal‐Modulated Nitrogen‐Doped Carbon Electrocatalyst for Efficient Carbon Dioxide Reduction

“…Expectedly, heteroatom‐doped carbons, such as single doping carbons (N−C, F−C) and multiple doping carbons (Si−C−N, NS−C, Fe(Ni, Co)−N−C, Ni(Mn)−Fe−N), and defective carbons were reported as electrocatalysts in this burgeoning field. The promoting effects by heteroatom incorporation in carbons were mainly concluded to be the modified orbital energy level via altering charge/spin distribution, as well as the reduced band gap for formation of highly active centers . To achieve the optimal control, many aspects such as dopant types, levels and surface distribution states should be considered toward enhancing the breakage of stable C=O bond (806 kJ mol −1 ) of CO 2 molecule and the subsequent reduction processes.…”

“…[1][2][3][4] Among these reactions, electrochemical CO 2 reduction reaction (CDRR) attracted great research interests recently because it is an approach to consuming CO 2 and producing value-added fuels or chemicals concurrently. [5][6][7] Expectedly, heteroatom-doped carbons, such as single doping carbons (NÀ C, [8][9][10][11] FÀ C [12] ) and multiple doping carbons (SiÀ CÀ N, [13] NSÀ C, [14] Fe(Ni, Co)À NÀ C, [15][16][17][18] Ni (Mn)À FeÀ N [19,20] ), and defective carbons [21][22][23] were reported as electrocatalysts in this burgeoning field. The promoting effects by heteroatom incorporation in carbons were mainly concluded to be the modified orbital energy level via altering charge/spin distribution, as well as the reduced band gap for formation of highly active centers.…”

“…The promoting effects by heteroatom incorporation in carbons were mainly concluded to be the modified orbital energy level via altering charge/spin distribution, as well as the reduced band gap for formation of highly active centers. [1,4,13,16] To achieve the optimal control, many aspects such as dopant types, levels and surface distribution states should be considered toward enhancing the breakage of stable C=O bond (806 kJ mol À 1 ) [24,25] of CO 2 molecule and the subsequent reduction processes. In spite of much progress in heteroatom-doped carbon catalysts for CDRR, the functional mechanisms of heteroatom dopants are still in controversy and their modulation approaches are limited, which remain huge room for further exploitation.…”