Non‐N‐Doped Carbons as Metal‐Free Electrocatalysts

Abstract

Ten years have passed since the discovery of the first nitrogen‐doped carbon‐based metal‐free catalyst for the oxygen reduction reaction, which opened a new field of catalysis toward a large variety of important applications, ranging from energy conversion and storage to environmental remediation. Various heteroatom‐doped carbons, beyond nitrogen‐doping (N‐doping), with distinctive features have also been developed for many specific reactions of practical significance (e.g., oxygen reduction (ORR), water splitting (OER and HER), CO2 reduction (CO2RR), and N2 reduction (NRR)). However, the topic of metal‐free non‐N‐doped carbon electrocatalysts has not been reviewed till now. This article aims to review recent advances in non‐N‐doped carbon electrocatalysts with an emphasis on their synthesis, catalytic mechanisms, and catalytic performance in various electrochemical reactions, including the ORR, OER, HER, H2O2 production, NRR, and CO2RR. Like N‐doping, boron‐doping, phosphorus‐doping, and fluorine‐doping are found to show similar catalytic efficiency for the ORR, OER, and HER. However, oxygen‐doping and boron‐doping are particularly favorable for the selective production of H2O2 and NH3, respectively, exceeding the performance of N‐doping. Along with the timely and critical overview on the non‐N‐doped carbon electrocatalysts, current challenges and future perspectives for this emerging field are also discussed.

Single Step Electrochemical Semi‐Exfoliated S‐Doped Graphene‐Like Structures from Commercial Carbon Fiber as Efficient Metal‐Free Catalyst for Hydrogen Evolution Reaction

“…Although the electro- ChemElectroChem negativity of sulfur is close to carbon and adding sulfur into crystal lattice is not change charge distribution dramatically, due to the spin density theory, catalytic activity can enhance with sulfur doping. [80] On the other hand, oxygen-containing groups (i. e., hydroxyl, carbonyl, carboxyl) which have acidic nature can boost the electrocatalytic activity of HER with reduction of the absorbed proton within acidic media. [80] However, remarkable performance differences between SÀ GrFs can correspond to S-doping level and the amount of oxygenated functional groups besides morphology which affects the mass transfer mechanism during HER.…”

“…[80] On the other hand, oxygen-containing groups (i. e., hydroxyl, carbonyl, carboxyl) which have acidic nature can boost the electrocatalytic activity of HER with reduction of the absorbed proton within acidic media. [80] However, remarkable performance differences between SÀ GrFs can correspond to S-doping level and the amount of oxygenated functional groups besides morphology which affects the mass transfer mechanism during HER. According to XPS survey spectra results, SÀ GrOF1 and SÀ GrF1 have oxygen and sulfur-containing functional groups among all catalysts (Figure S5).…”

Phosphorus-Doped Graphene Electrocatalysts for Oxygen Reduction Reaction

“…When the carbon atoms in the graphene lattice are partially substituted by heteroatoms, the structure and electronic properties of the heteroatoms-doped graphene can be dramatically altered by the specific characters of the dopants. Usually, the neighboring elements of the carbon, such as nitrogen(N), boron(B), oxygen(O), phosphorus(P), sulfur(S), and fluorine(F), are preferred as the dopants for graphene [ 25 , 26 ]. Depending on their atom size, electronegativity, and doping level, the adsorption behavior, the chemisorption energy, and the active sites of the doped graphene can be modulated.…”

“…The ORR performance can be remarkably enhanced in nitrogen-doped graphene (N-graphene), which has been demonstrated and reviewed in previous works [ 27 , 28 , 29 ]. Besides, many previous articles reviewed the synthesis methods and the application of different heteroatoms-doped graphene (X-graphene) [ 25 , 30 , 31 ]. However, a limited number of articles focused on phosphorus-doped graphene (P-graphene).…”

Surface Diels–Alder adducts on multilayer graphene for the generation of edge-enriched single-atom FeN4 sites for ORR and OER electrocatalysis

“…Fe or Co) to obtain optimal electronic and geometric structures. [14][15][16][17][18][19][20][21] More concretely, density functional theory (DFT) calculations suggested that co-doping of Fe and N in the form of possible FeN 4 sites on a graphitic substrate could be as active as Pt for O 2 adsorption and subsequent O]O bond breaking during the ORR. [22][23][24][25] In this sense, nitrogen-containing functional groups on a graphitic matrix also play a fundamental role in the performance and electronic conductivity of electrocatalytic processes.…”