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

Abstract

Afacile route to scalable production of Nand Scodoped, hierarchically porous carbon nanofiber (NSHCF) membranes (ca. 400 cm 2 membrane in as ingle process) is reported. As-synthesized NSHCF membranes are flexible and free-standing,allowing their direct use as cathodes for efficient electrochemical CO 2 reduction reaction (CO 2 RR). Notably, CO with 94 %F aradaic efficiency and À103 mA cm À2 current density are readily achieved with only about 1.2 mg catalyst loading, which are among the best results ever obtained by metal-free CO 2 RR catalysts.O nt he basis of control experiments and DFT calculations,s uch outstanding CO Faradaic efficiency can be attributed to the co-doped pyridinic Na nd carbon-bonded Sa toms,w hiche ffectively decrease the Gibbs free energy of key *COOH intermediate.F urthermore,h ierarchically porous structures of NSHCF membranes impart am uchh igher density of accessible active sites for CO 2 RR, leading to the ultra-high current density.Electrochemical reduction of CO 2 in aqueous solution has been widely recognized as apromising strategy for alleviating the concerns on the increasing level of atmospheric CO 2 concentration. This is because CO 2 reduction can be readily conducted in aqueous solution, electrically driven from renewable energy sources,a nd produce value-added fuels or chemicals. [1][2][3] Electrochemical catalytic CO 2 RR, especially for potential industrial-scale applications,depends heavily on stable,r ecyclable,a nd sustainable catalysts,w hich can retain their good performance at large current density (> 100 mA cm À2 ). [4,5] Thep ast decades have witnessed metals (such as Ag, [6] Pd, [7] Au, [8] Co [9] )a nd their derivatives (that is,m etal oxides and metal complexes) as the most commonly used electrocatalysts for efficient CO 2 RR. [6][7][8][9][10][11][12][13][14][15] However,these traditional

Electrochemical Reduction of CO2 to CO by N,S Dual‐Doped Carbon Nanoweb Catalysts

“…In contrast, granular structured catalysts with small particles and without a nanowire morphology (Figure S3 in the Supporting Information) were derived from PPy if surfactants were not used in the polymerization step. The HRTEM images of an individual NSCNW‐3 nanowire indicated that the lattice spacing was approximately 0.35 nm, corresponding to the (2 0 0) plane of graphitic carbon (inset of Figure c) . Electron energy loss spectroscopy (EELS) was also conducted to explore the doping states of N and S atoms.…”

“…It is recognized that the formation of adsorbed COOH intermediates (*COOH) is the rate‐determining step for the CO 2 reduction because the CO production can be restrained by a high Gibbs free energy of the *COOH formation . Previous theoretical calculations revealed that a lower Gibbs free‐energy barrier for *COOH formation occurs in a pyridinic N adjacent to the thiophene‐like S, whereas a higher Gibbs free energy on pyridinic N species requires extra energy to overcome the barrier of *COOH formation . In addition, the incorporation of F atoms with an electron‐donating nature into N‐doped carbons could alter the electronic properties of pyridinic N, which helps to boost the CO 2 activation for CO production .…”

“…reported a significant enhancement in CO 2 RR activity for CO production by incorporating fluorine (F) atoms into N‐doped carbons, suggesting that the electron donation from F could improve the intrinsic catalytic activity and selectivity of pyridinic N for CO production . It has also been reported that additional S doping in N‐doped carbons could further reduce the Gibbs free energy of formation of *COOH as the rate‐determining step for the CO 2 ‐to‐CO conversion . In addition, to improve the efficiency of the CO 2 RR, the construction of a 3 D nanostructure with a large surface can provide a higher probability of exposed active sites and facilitate the rapid transport of electrons and CO 2 RR‐related species .…”

“…[22] It has also been reported that additional S doping in N-doped carbons could furtherr educe the Gibbs free energy of formation of *COOH as the rate-determining step for the CO 2 -to-CO conversion. [23] In addition, to improve Converting CO 2 into useful chemicals through an electrocatalytic process is an attractive solution to reduce CO 2 in the atmosphere. However,t he process suffers from high overpotential, low activity,o rp oor product selectivity.I nt his study,N ,S dual-doped carbon nanoweb (NSCNW) materials were proposed as an efficient nonmetallic electrocatalyst for CO 2 reduction.…”

One‐dimensional Nanomaterial Electrocatalysts for CO2Fixation

“…[60] Copyright 2018,W iley-VCH. selectively electroreduction CO 2 to CO. [60] The preparation process of NSHCF was shown in Figure7e, and Figure 7f revealed that the elements of C, N, and Sw ere uniformly distributed. The obtainedp orousn etwork-like NSHCF were composed of nanofibersw ith diameters ranging from 500 to 1000 nm.…”