Double‐atom catalysts (DACs) have emerged as a novel frontier in heterogeneous catalysis because the synergistic effect between adjacent active sites can promote their catalytic activity while ...maintaining high atomic utilization efficiency, good selectivity, and high stability originating from the atomically dispersed nature. In this review, the recent progress in both experimental and theoretical research on DACs for various catalytic reactions is focused. Specifically, the central tasks in the design of DACs—manipulating the synergistic effect and engineering atomic and electronic structures of catalysts—are systematically reviewed, along with the prevailing experimental, characterization, and computational modeling approaches. Furthermore, the practical applications of DACs in water splitting, oxygen reduction reaction, nitrogen reduction reaction, and carbon dioxide reduction reaction are addressed. Finally, the future challenges for DACs are summarized and an outlook on the further investigations of DACs toward heterogeneous catalysis in high‐performance energy and environmental applications is provided.
Double‐atom catalysts (DACs) have emerged as a new frontier of heterogeneous catalysis with promoted catalytic activity from the synergistic effect between adjacent active sites. Manipulating the synergistic effect and engineering atomic and electronic structures of catalysts are central tasks in the design of DACs. In this review, experimental and theoretical approaches and practical applications are introduced.
This paper reviews recent progress made in identifying electrocatalysts for carbon dioxide (CO
2
) reduction to produce low-carbon fuels, including CO, HCOOH/HCOO
−
, CH
2
O, CH
4
, H
2
C
2
O
4
/HC
2
...O
4
−
, C
2
H
4
, CH
3
OH, CH
3
CH
2
OH and others. The electrocatalysts are classified into several categories, including metals, metal alloys, metal oxides, metal complexes, polymers/clusters, enzymes and organic molecules. The catalyts' activity, product selectivity, Faradaic efficiency, catalytic stability and reduction mechanisms during CO
2
electroreduction have received detailed treatment. In particular, we review the effects of electrode potential, solution-electrolyte type and composition, temperature, pressure, and other conditions on these catalyst properties. The challenges in achieving highly active and stable CO
2
reduction electrocatalysts are analyzed, and several research directions for practical applications are proposed, with the aim of mitigating performance degradation, overcoming additional challenges, and facilitating research and development in this area.
This paper reviews recent progress made in identifying electrocatalysts for carbon dioxide (CO
2
) reduction to produce low-carbon fuels, including CO, HCOOH/HCOO
−
, CH
2
O, CH
4
, H
2
C
2
O
4
/HC
2
O
4
−
, C
2
H
4
, CH
3
OH, CH
3
CH
2
OH and others.
A comprehensive overview and description of graphene‐based nanomaterials explored in recent years for catalyst supports and metal‐free catalysts for polymer electrolyte membrane (PEM) fuel cell ...oxygen reduction reactions (ORR) is presented. The catalyst material structures/morphologies, material selection, and design for synthesis, catalytic performance, catalytic mechanisms, and theoretical approaches for catalyst down‐selection and catalyzed ORR mechanisms are emphasized with respect to the performance of ORR catalysts in terms of both activity and stability. When graphene‐based materials, including graphene and doped graphene, are used as the supporting materials for both Pt/Pt alloy catalysts and non‐precious metal catalyst, the resulting ORR catalysts can give superior catalyst activity and stability compared to those of conventional carbon‐supported catalysts; when they are used as metal‐free ORR catalysts, significant catalytic activity and stability are observed. The nitrogen‐doped graphene materials even show superior performance compared to supported metal catalysts. Challenges including the lack of material mass production, unoptimized catalyst structure/morphology, insufficient fundamental understanding, and testing tools/protocols for performance optimization and validation are identified, and approaches to address these challenges are suggested.
A comprehensive overview and description of graphene‐based nanomaterials for catalyst supports and metal‐free catalysts for polymer electrolyte membrane (PEM) fuel cell oxygen reduction reactions (ORR) is presented. The catalyst material selection, design, synthesis, and characterization, as well as a theoretical understanding of the catalysis process and mechanisms are discussed. The challenges and their corresponding approaches, in addition to directions for future perspectives and research are suggested.
Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, ...pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (
e.g.
, a high power density and a long cycle-life) (507 references).
Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes.
Metal–nitrogen–carbon (M–N–C) material with specifically coordinated configurations is a promising alternative to costly Pt‐based catalysts. In the past few years, great progress is made in the ...studies of M–N–C materials, including the structure modulation and local coordination environment identification via advanced synthetic strategies and characterization techniques, which boost the electrocatalytic performances and deepen the understanding of the underlying fundamentals. In this review, the most recent advances of M–N–C catalysts with specifically coordinated configurations of M–Nx (x = 1–6) are summarized as comprehensively as possible, with an emphasis on the synthetic strategy, characterization techniques, and applications in typical electrocatalytic reactions of the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, CO2 reduction reaction, etc., along with mechanistic exploration by experiments and theoretical calculations. Furthermore, the challenges and potential perspectives for the future development of M–N–C catalysts are discussed.
Metal–nitrogen–carbon (M–N–C) materials with specifically coordinated configurations have attracted board interest in energy storage and conversion technologies. A detailed summary of the M–N–C catalysts, including synthetic strategies, characterization techniques, and the typical electrochemical redox reactions, is particularly important to comprehensively understand the catalytic mechanism in‐depth and rationally design high active M–N–C catalysts with specific configurations.
Highlights
General principles for designing atomically dispersed metal-nitrogen-carbon (M–N-C) are briefly reviewed.
Strategies to enhance the bifunctional catalytic performance of atomically ...dispersed M–N-C are summarized.
Challenges and perspectives of M–N-C bifunctional oxygen catalysts for Rechargeable zinc-air batteries are discussed.
Rechargeable zinc-air batteries (ZABs) are currently receiving extensive attention because of their extremely high theoretical specific energy density, low manufacturing costs, and environmental friendliness. Exploring bifunctional catalysts with high activity and stability to overcome sluggish kinetics of oxygen reduction reaction and oxygen evolution reaction is critical for the development of rechargeable ZABs. Atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts possessing prominent advantages of high metal atom utilization and electrocatalytic activity are promising candidates to promote oxygen electrocatalysis. In this work, general principles for designing atomically dispersed M-N-C are reviewed. Then, strategies aiming at enhancing the bifunctional catalytic activity and stability are presented. Finally, the challenges and perspectives of M-N-C bifunctional oxygen catalysts for ZABs are outlined. It is expected that this review will provide insights into the targeted optimization of atomically dispersed M-N-C catalysts in rechargeable ZABs.
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•Porous carbons (PCs) with customizable small mesopore were synthesized from coal tar pitch.•The mesopore development of PCs depends on the content of light components in ...precursor.•The contribution of small mesopores to the performance of supercapacitors is discussed.•The supercapacitor delivers a superior energy density of 0.15 mW h cm−2.
The advancement of modern carbon-based supercapacitor depends strongly on the porous carbons (PCs) with tailoring pore configuration. To achieve the trade-off between power density and energy density, enriching small mesopore in PCs is an important but challenging research subject. Herein, the PCs with customizable small mesopores were fabricated from cheap coal tar pitch (CTP) by adjusting their content of light component (i.e. toluene soluble CTP, TS). The share of small mesopore in total pore structure of PCs (V2–4 nm/Vtotal) progressively increases with the lifting TS content of precursor. Consequently, the specific surface area and pore volume of PCs increase first and then decrease as the TS content increases. Simultaneously, the influence of small mesopore on the capacitance performances of supercapacitors was reflected in their capacitance, rate capability, cycle stability and self-discharge performance. The supercapacitor assembled by the PC with a V2–4 nm/Vtotal of ~31.3% delivers a superior energy density of 0.15 mW h cm−2 at a power density of 5.40 mW cm−2. Therefore, the small mesopore engineering in carbon materials derived from inexpensive precursors broadens the avenue to further improve the areal capacitive performance of supercapacitors by a facile up-scalable approach.
In this study, mechanical vibration is used for hydrogen generation and decomposition of dye molecules, with the help of BiFeO3 (BFO) square nanosheets. A high hydrogen production rate of ≈124.1 μmol ...g−1 is achieved under mechanical vibration (100 W) for 1 h at the resonant frequency of the BFO nanosheets. The decomposition ratio of Rhodamine B dye reaches up to ≈94.1 % after mechanical vibration of the BFO catalyst for 50 min. The vibration‐induced catalysis of the BFO square nanosheets may be attributed to the piezocatalytic properties of BFO and the high specific surface area of the nanosheets. The uncompensated piezoelectric charges on the surfaces of BFO nanosheets induced by mechanical vibration result in a built‐in electric field across the nanosheets. Unlike a photocatalyst for water splitting, which requires a proper band edge position for hydrogen evolution, such a requirement is not needed in piezocatalytic water splitting, where the band tilting under the induced piezoelectric field will make the conduction band of BFO more negative than the H2/H2O redox potential (0 V) for hydrogen generation.
Good vibrations! BiFeO3 can serve as a piezocatalyst for hydrogen production by harvesting vibration energy from the environment. The strong piezoelectric field induced by mechanical vibrations tilts the conduction band of BiFeO3, making it more negative than the H2/H2O redox potential, thus enabling hydrogen evolution (see picture).
Novel proton-conducting polymer electrolyte membranes have been prepared from bacterial cellulose by incorporation of phosphoric acid (H3PO4/BC) and phytic acid (PA/BC). H3PO4 and PA were doped by ...immersing the BC membranes directly in the aqueous solution of H3PO4 and PA, respectively. Characterizations by FTIR, TG, TS and AC conductivity measurements were carried out on the membrane electrolytes consisting of different H3PO4 or PA doping level. The ionic conductivity showed a sensitive variation with the concentration of the acid in the doping solution through the changes in the contents of acid and water in the membranes. Maximum conductivities up to 0.08 S cm−1 at 20 °C and 0.11 S cm−1 at 80 °C were obtained for BC membranes doped from H3PO4 concentration of 6.0 mol L−1 and, 0.05 S cm−1 at 20 °C and 0.09 S cm −1 at 60 °C were obtained for BC membranes doped from PA concentration of 1.6 mol L−1. These types of proton-conducting membranes share not only the good mechanical properties but also the thermal stability. The temperature dependences of the conductivity follows the Arrhenius relationship at a temperature range from 20 to 80 °C and, the apparent activation energies (Ea) for proton conduction were found to be 4.02 kJ mol−1 for H3PO4/BC membrane and 11.29 kJ mol−1 for PA/BC membrane, respectively. In particular, the membrane electrode assembly fabricated with H3PO4/BC and PA/BC membranes reached the initial power densities of 17.9 mW cm−2 and 23.0 mW cm−2, which are much higher than those reported in literature in a real H2/O2 fuel cell at 25 °C.
► Two proton-conducting membranes were prepared by immersing bacterial cellulose (BC) into H3PO4 and PA. ► H3PO4/BC membrane showed a high proton conductivity of 0.15 S cm−1. ► PA/BC membrane showed a high proton conductivity of 0.08 S cm−1. ► The MEA fabricated with H3PO4/BC showed an initial power density of 17.9 mW cm−2. ► The MEA fabricated with PA/BC showed an initial power density 23.0 mW cm−2.
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