Carbon-Based Metal-Free Electrocatalysis for Energy Conversion, Energy Storage, and Environmental Protection

Abstract

Carbon-based metal-free catalysts possess desirable properties such as high earth abundance, low cost, high electrical conductivity, structural tunability, good selectivity, strong stability in acidic/alkaline conditions, and environmental friendliness. Because of these properties, these catalysts have recently received increasing attention in energy and environmental applications. Subsequently, various carbon-based electrocatalysts have been developed to replace noble metal catalysts for low-cost renewable generation and storage of clean energy and environmental protection through metal-free electrocatalysis. This article provides an up-to-date review of this rapidly developing field by critically assessing recent advances in the mechanistic understanding, structure design, and material/device fabrication of metal-free carbon-based electrocatalysts for clean energy conversion/storage and environmental protection, along with discussions on current challenges and perspectives. Graphical AbstractKeywords Metal-free electrocatalysis · Carbon-based catalysts · Energy conversion and storage · Environmental protection

Uniform Virus‐Like Co–N–Cs Electrocatalyst Derived from Prussian Blue Analog for Stretchable Fiber‐Shaped Zn–Air Batteries

“…Over the last decade, a wide range of transition metal‐based and metal free carbon materials have been found to be electroactive and suitable for ORR and OER. Examples for these materials include transition metal–nitrogen–doped carbons (M–N–C), transition metal oxides, nitrides/carbides/sulfides, and metal‐free heteroatom‐doped carbon materials . Among these, the M–N–C materials and their composites have been reported as promising alternatives for noble metal‐based catalysts owing to the synergetic effect of M and N co‐doping that enhances their catalytic performance .…”

“…Examples for these materials include transition metal-nitrogen-doped carbons (M-N-C), [19,20] transition metal oxides, [21] nitrides/carbides/sulfides, [22][23][24] and metal-free heteroatom-doped carbon materials. [25][26][27] Among these, the M-N-C materials and their composites have been reported as promising alternatives for noble metal-based catalysts owing to the synergetic effect of M and N co-doping that enhances their catalytic performance. [28][29][30] In addition to the synergetic codoping effects, it is widely accepted that the structural design of M-N-C materials is also crucial, as different structures result in changes in the surface area and electronic conductivity, which are important factors in determining the catalysts' electrochemical performance.…”

Co9S8‐Catalyzed Growth of Thin‐Walled Graphite Microtubes for Robust, Efficient Overall Water Splitting

“…[4][5][6][7] Twos imple reactions, the oxygen evolution reaction (OER) and hydrogen evolutionr eaction( HER), are critical for current energyc onversion technologies. [8][9][10][11][12] Co 9 S 8 is ap romising materialt hat has been demonstrated to have superb electrochemical performance for a varietyo fa pplications,f or instance, lithium-ion ands odium-ion batteries, supercapacitors, HER, and OER. However,t he high cost and limitedr eserves of noble metals greatlyp rohibit their largescale commercial applications.…”

Doping of Carbon Materials for Metal‐Free Electrocatalysis

“…While metal alloys often suffer from segregation problems, heteroatom-doped carbonbased metal-free catalysts (C-MFCs) with covalent chemical bonds between the carbon and dopant atoms have no segregation issue, leading to a good operational stability. [5] Furthermore, 3D carbon architectures can be constructed from advanced nanocarbons, including carbon nanotubes (CNTs) and graphene sheets, [9,10] to further improve the performance of C-MFCs. However, the catalytic active sites on C-MFCs can be modulated by introducing different dopants and structural defects, [8] providing powerful means for creating a large variety of highly efficient, multifunctional catalysts for various reactions.…”

“…[8] It is the doping-induced charge transfer from carbon atoms to their adjacent nitrogen atoms, changing the chemisorption mode of O 2 and weakening the OO bond for improving the ORR performance of VA-NCNT. [4,5,7] Since then, C-MFCs have been demonstrated to catalyze hydrogen evolution reaction (HER) for the production of clean fuel (H 2 ) from photo-/electrochemical water-splitting, ORR in fuel cells for energy generation/conversion, [10] and oxygen evolution reaction (OER) in metal-air batteries for energy storage, [7] two-electron transfer ORR to generate H 2 O 2 (an energy carrier and green oxidizer), [13] CO 2 reduction reaction (CO 2 RR) for the direct conversion of CO 2 into fuel, [14] N 2 reduction reaction (NRR) for synthesis of NH 3 under ambient environment, [15] and for the renewable energy generation/conversion from water driven by sunlight. [4,5,7] Since then, C-MFCs have been demonstrated to catalyze hydrogen evolution reaction (HER) for the production of clean fuel (H 2 ) from photo-/electrochemical water-splitting, ORR in fuel cells for energy generation/conversion, [10] and oxygen evolution reaction (OER) in metal-air batteries for energy storage, [7] two-electron transfer ORR to generate H 2 O 2 (an energy carrier and green oxidizer), [13] CO 2 reduction reaction (CO 2 RR) for the direct conversion of CO 2 into fuel, [14] N 2 reduction reaction (NRR) for synthesis of NH 3 under ambient environment, [15] and for the renewable energy generation/conversion from water driven by sunlight.…”