Carbon Solving Carbon's Problems: Recent Progress of Nanostructured Carbon‐Based Catalysts for the Electrochemical Reduction of CO₂

Abstract

The electrochemical reduction of CO2 to useful molecules offers an elegant technological solution to current energy security and sustainability issues because it sequesters carbon from the atmosphere, provides an energy storage solution for intermittent renewable sources, and can be used to produce fuels and industrial chemicals. Nanostructured carbon materials have been extensively used to catalyse some key electrochemical processes because of their excellent electrical conductivity, chemical stability, and abundant active sites. This progress report focuses on nanostructured carbon materials, namely graphene materials, carbon nanotubes, porphyrin materials, nanodiamond, and glassy carbon, which have recently shown promise as high performing CO2 reduction electrocatalysts and supports. Along with discussion regarding materials synthesis, structural characterisation, and electrochemical performance characterisation techniques used, this report will discuss the findings of recent computational CO2RR studies which have been key to elucidating active sites and reaction mechanisms, and developing strategies to break conventional scaling relationships. Lastly, challenges and future perspective of these carbon‐based materials for CO2 reduction applications will be given. Much work is still required to realise the commercial viability of the technology, but advanced experimental techniques coupled with theoretical calculations are expected to facilitate future development of the technology.

A Core–Shell‐Structured Silver Nanowire/Nitrogen‐Doped Carbon Catalyst for Enhanced and Multifunctional Electrofixation of CO2

“…However, as ingle catalyst showing activity in both solvent types is still rare, to the best of our knowledge.W ed eveloped ac ore-shell-structured AgNW/NC700 composite using aA gn anowire( NW) core encapsulated by aN -doped carbon (NC) shell at 700 8C. [10][11][12][13][14][15] In particular, Ag-based catalysts could selectivelyc onvertC O 2 into CO, which is widely used as syngasi nc hemical industry. Under mild conditions, up to 96 %faradaic efficiency of CO, 95 %yield of Ibuprofen and 92 %y ield of propylene carbonate could be obtained in the electrochemical CO 2 direct reduction,c arboxylation and cycloaddition,respectively,using the same AgNWs/NC700 catalyst.…”

Catalytic Mechanisms and Design Principles for Single‐Atom Catalysts in Highly Efficient CO2 Conversion

“…

energy such as wind and solar energy has attracted enormous interest for its significant roles in mitigating CO 2 emissions and reducing dependence on petrochemicals. [3] The former involves associated multielectron transfer process and is difficult to accurately control the reaction process by external conditions, [4] while the latter is mainly due to the fact that the equilibrium potentials for most of the CO 2 RR are very close to hydrogen evolution reaction (HER) toward undesirable side-products in aqueous electrolytes, which degrades the electrocatalytic performance during the CO 2 RR process. To date, the electrocatalysts have confronted severe bottlenecks issue: poor selectivity about various accessory products in CO 2 conversion process, and loss of efficiency toward competing hydrogen evolution.

…”

Composition Tailoring via N and S Co‐doping and Structure Tuning by Constructing Hierarchical Pores: Metal‐Free Catalysts for High‐Performance Electrochemical Reduction of CO2

“…Thecurrent density of NSHCF900 maintained as teady value at approximately À100 mA cm À2 with no significant decay (Figure 2e), and the corresponding Faradaic efficiency of CO only decreased slightly to 93 % (Figure 2f)throughout the stability test. Fort he NSHCF900 composite,t he achievable maximum Faradaic efficiency (94 %) of CO is comparable to those of state-of-the-art electrocatalysts,r egardless of metal-based or metal-free catalysts.C ompared to those reported state-of-the-art metal-free electrocatalysts, [18,19] using relatively low catalyst loading, NSHCF900 yielded one of the highest current densities (À103 mA cm À2 ), which is one of the best metalfree electrocatalysts for electrochemical reduction of CO 2 to CO. Figure S14 shows that NSHCF900 retained well-distributed hollow nanocages within the carbonaceous nanofibers.T he EDX mappings of an individual NSHCF900 nanofiber demonstrated that C, N, and Se lements were still uniformly distributed, indicating the robust electrochemical stability and reusability of NSHCF900.…”

“…[21] TheT afel slope of 159, 192, and 132 mV dec À1 indicated the poor kinetics on NSHCF800, NSHCF1000, and NSCF900. [18][19][20][21][22][23][24][25] In our study,N-doped hierarchically porous carbon nanofiber (NHCF900;S upporting Information, Figure S15) only yields 63 %F aradaic efficiencyfor CO in CO 2 RR, which is significantly lower than that of NSHCF900, signifying the importance of Ss pecies.T he relationship between the nitrogen and sulfur contents in catalysts and the associated CO 2 RR activity is illustrated in the Supporting Information, Figure S16, which demonstrates that pyridinic Ni st he dominant active sites for CO 2 RR, and the presence of carbon-bonded Sc an greatly enhance the catalytic activity. [20,31] We hypothesize that the doped species within NSHCF is the origin of the disparity in the catalytic activity (for example,N -doped carbons have excellent CO 2 RR capabilities).…”

“…These metal-free carbon electrocatalysts are cost-effective and possess good conductivity and allow for the doping with heteroatoms. [18,19] Herein, we report ar obust and scalable strategy for synthesis of nitrogen and sulfur co-doped, hierarchically porous carbon nanofiber (NSHCF) membranes via electrospinning for high-efficiency,m etal-free CO 2 RR. [21] Although good product selectivity or high Faradaic efficiencies were occasionally reported, nanostructured carbon catalysts that maintain good efficiency at high current density are still comparatively few and limited in scope.…”