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Development of earth-abundant and robust oxygen evolution reaction (OER) catalysts is imperative for cost-effective hydrogen production via water electrolysis. Herein, we report ultrafine iron (oxy)hydroxide nanoparticles with average particle size of 2.6 nm and abundant surface defects homogeneously supported on oleum-treated graphite (FeO

Compared with commercial MoO3, α-MoO3 modified MCM-22 possesses more Mo species in the zeolite pores, more MoCx active sites, and fewer Brønsted acid sites.

Direct conversion of solid g-C3N4 into Co-ended N-doped carbon nanotubes as bifunctional electrocatalyst with ORR and OER activity for efficient rechargable Zn-air batteries.

Mesoporous Mn–Fe oxyhydroxides exhibit excellent OER performance with overpotential of 275 mV, where the surface doping of Fe onto the MnOOH can favorably destabilize the surface bridge O atoms and promote the formation of surface oxygen vacancies.

The key challenge for scalable production of hydrogen from water lies in the rational design and preparation of high-performance and earth-abundant electrocatalysts to replace precious metal Pt and IrO2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Although atomic M-N-C materials have been extensively studied in heterogeneous catalysis field, the insufficient antioxidant capacity of carbonous substrates hinders their practical application in OER. Developing highly active and stable OER electrocatalysts is the key for electrochemical water splitting. This review presents feasible design strategies for fabricating carbon-free single-site catalysts and their applications in HER/OER and overall water splitting. The constitutive relationships between structure, composition, and catalytic performance for HER and OER are detailly discussed, providing ponderable insights into rationally constructing high-performance HER and OER electrocatalysts. The perspectives on the challenges and future research orientations in single-site catalysts for electrochemical water splitting are suggested.

Owning to unsaturated coordination environment, quantum size effect and metal-support interaction, single- or dual-atom metal sites, such as Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Ag, Sn, Ir, Pt, Au, Bi, and Er coordinated with nonmetallic elements such as O, N, P, and S, exhibit different electronic configurations, which endow them with high catalytic performances in multiple redox reactions and versatile applications in organic synthesis, environmental remediation, energy conversion, and biomedicine. Despite intense research, the relation of structure-activity for single-atom catalysts (SACs) still bedazzles researchers, since diversified configurations of active sites would bring about difficulty in structural identification and theoretical simulations. Here, recent results on the applications of SACs are reviewed with an emphasis on identifying the active sites and discussing the relation between structure and property.

To solve the energy crisis and environmental pollution problems, the use of clean and renewable energy to replace fossil energy has become a top priority. The oxygen evolution reaction (OER) is the core of many renewable energy technologies. Developing low-cost and high-performance OER electrocatalysts is the key to implementing efficient energy conversion processes. Here, we synthesize ordered mesoporous iron-cobalt oxides using a hard template strategy. As a mesoporous oxide catalyst, meso-CoFe0.05Ox exhibits low OER overpotentials of 280 and 373 mV at current densities of 10 and 100 mA cm-2, respectively, and does not show deactivation for at least 18 hours at 100 mA cm-2. The introduction of iron can change the electronic structure of Co, and the orbital electrons are easily transferred from cobalt to iron. The enhanced OER performance can be attributed to concerted catalysis between the iron and cobalt sites that lowers the OER energy barrier, and the large specific surface area of the porous oxide providing efficient active sites for the reaction.

High specific activity of single-atom catalysts shows great application potentials in water splitting and fuel cell systems. Herein, we report a facile pyrolysis method to fabricate an atomically dispersed rhodium catalyst (Rh@NG). The Rh@NG exhibits outstanding electrochemical activities and kinetics for oxygen reduction reaction in alkaline medium, which can compare to Pt/C catalysts, along with excellent durability and good tolerance to methanol and carbon monoxide. The half-wave potential on Rh@NG in 0.1 M KOH and 0.1 M HClO4 is 0.848 and 0.74 V vs RHE, respectively. Additionally, the Rh@NG displays superior performance for hydrogen evolution reaction, offering a low overpotential of only 29, 33, and 45 mV at 10 mA cm−2 in 0.5 M H2SO4, 1.0 M KOH, and 0.1 M KOH, respectively. Theoretical calculations reveal that the efficient active sites for HER and ORR might be RhN3 and RhN4 moiety embedded into the N-doped graphene, respectively.

Development of low-cost and high-efficiency electrocatalysts toward bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial for reversible fuel cells. Herein, we fabricate an N/P-codoped Fe/Co/Ni-containing graphene-based material by deriving metal–organic frameworks (MOFs). The homogeneous dispersion of tri-metallic Fe/Co/Ni in the MOF-derived carbon materials favors the formation of heterojunctions between the resulted different phosphides, which speed up electron transfer and improve the electrocatalytic properties. The graphene support can efficiently protect the phosphides from degradation during the catalytic process. The obtained FeCoNiP@NC catalyst shows low HER overpotential of 93 and 187 mV at a current density of 10 mA cm−2 in 0.5 M H2SO4 and 1.0 M KOH, respectively. In addition, The FeCoNiP@NC exhibits low OER overpotential of 266 mV at 10 mA cm−2 in 1.0 M KOH solution. The FeCoNiP@NC electrocatalyst can work as bifunctional electrode materials for overall water splitting in alkaline electrolyte with good stability. FeP and CoP play a dominant role in HER, while CoP plays a main role in OER.

Ammonia can not only be used as an active nitrogen component of nitrogen fertilizers, fibers, explosives, etc., but also provides a high energy density and carbon free energy carrier. Currently, ammonia is industrially synthesized by the Haber Bosch process at high temperature and high pressure, which results in high energy loss and a serious greenhouse effect. The electrocatalytic nitrogen reduction reaction (NRR) is a sustainable and environmentally friendly strategy for the synthesis of ammonia. Although lots of electrocatalysts have been developed for this reaction, further breakthroughs are needed in catalytic activity, selectivity and Faraday efficiency to meet the large-scale commercial demand. In this review, the recent advance in NRR electrocatalysis is thoroughly commented on. Different kinds of electrocatalysts used in ammonia synthesis (including single atom catalysts, metal oxide catalysts, nanocomposite catalysts, and metal free catalysts) are introduced. The reaction mechanism of the NRR is discussed in detail. The structure-function relationship and efficient strategies to improve the ammonia yield are clearly discussed. The effect of the electronic structure and morphology of catalysts on the selectivity of the NRR is highlighted. The research directions and perspectives on the further development of more efficient electrocatalysts for the NRR are provided.

The water oxidation reaction is the pivotal half-reaction for photo-/electro-catalytic water splitting. Fabrication of high-efficiency and robust water oxidation is essential to realize wide-scale artificial photosynthesis. Here, we report an efficient strategy to improve the water oxidation activity of iridium oxide by a nitrogen-coordination method. Due to the coordination effect, the iridium oxide can be well dispersed to generate ultra-small nanoparticles and the intrinsic activity can be improved for the water oxidation reaction. This study suggests that high-performance water oxidation catalysts can be constructed based on a nitrogen-coordination strategy.

Development of high-efficiency single-atom catalysts (SACs) for the oxygen evolution reaction (OER) is challenging. Herein, we report a facile annealing strategy to construct an atomically dispersed cobalt- and nitrogen-codoped graphene catalyst for high-efficiency OER. The as-prepared 0.7-Co@NG-750 electrocatalyst requires an ultra-low onset overpotential of approximately 210 mV on a glassy carbon electrode in both 1.0 M KOH and 0.1 M KOH solutions. The density functional theory (DFT) calculations reveal that the theoretical overpotential on Co–N4 and Co–N2C2 sites is 0.41 and 0.53 V, respectively, and these might be efficient active sites for electrocatalytic water oxidation.

Development of high-performance multifunctional electrocatalysts is of great interest for renewable energy systems. Here, an atomically dispersed iridium embedded nitrogen-doped graphene electrocatalyst (Ir@NG-750) is synthesized through a simple annealing method. The atomic Ir@NG-750 catalyst exhibits excellent electrocatalytic performance for the oxygen reduction reaction in both acidic and alkaline media with half-wave potentials of 0.77 V and 0.865 V, respectively, together with good durability, a four-electron pathway, and excellent resistance to carbon monoxide poisoning. It also shows outstanding electrochemical performance for the hydrogen evolution reaction, providing low overpotentials of 114 mV and 25 mV at 10 mA cm−2 in 0.1 M KOH and 0.5 M H2SO4, respectively. Moreover, it displays superior catalytic performance for the oxygen evolution reaction with low overpotentials of 273 mV, 340 mV, and 371 mV at 10 mA cm−2, in 1.0 M KOH, 0.1 M KOH and 0.5 M H2SO4, respectively. Due to its excellent trifunctional properties, it can deliver an overall water splitting current density of 10 mA cm−2 at a cell voltage of 1.7 V. In addition, the Ir@NG-750-based Zn–air battery exhibits a peak power density of 56.8 mW cm−2 at a voltage of 0.62 V. DFT calculations reveal that the IrN4–G center is the active site for these reactions.

Improvement of the catalytic performance of oxygen evolution reaction (OER) is the key to the large-scale implementation of water electrolysis. Here, we report an efficient strategy to improve the OER activity of Co-based nanocomposite catalysts by adding Fe3+ ions into the electrolyte. The overpotential of cobalt tartrate annealed at 700 °C can be decreased from 360 to 329 mV by introducing 20 ppm Fe3+ into the alkaline electrolyte. Electrochemical measurements indicate that the introduction of Fe3+ can generate more efficient active sites by cooperation with Co species and promote OER kinetics, thus improving electrocatalytic performance.

Electrocatalytic water splitting is a feasible method to store solar, wind, and water energy in the form of hydrogen fuel. However, the sluggish oxygen evolution reaction (OER) limits the energy ef...

Development of high-efficiency atomic transition metal catalysts for oxygen electrode reactions is attractive for regenerative energy conversion and storage technologies. Here we report a facile approach to fabricate an atomic iron- and nitrogen-codoped graphene catalyst with high content of iron (up to 1.5 wt%). The atomic iron-based catalyst on glassy carbon electrodes displays low overpotential (194 mV and 275 mV) reported at 10 mA cm−2 in 1.0 M KOH and 0.1 M KOH solutions for the oxygen evolution reaction (OER), respectively. In addition, the atomic iron-based composite electrocatalyst exhibits a high half-wave potential of 0.90 V vs. RHE for the oxygen reduction reaction (ORR) in 0.1 M KOH, and a combined ORR and OER potential gap of 0.605 V. Structural characterization and theoretical calculations demonstrate that the efficient active sites for OER and ORR should be FeN4-moiety embedded into the graphene, on which the overpotential-determining step is the O O coupling step.

A high-efficiency trifunctional electrocatalyst is required for practical applications of regenerative fuel cells, because the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), an...

Development of effective transition metal catalysts to replace precious metal platinum-based electrocatalysts for hydrogen evolution reaction (HER) has attracted widespread interest. Metal–organic framework (MOF) is an organic–inorganic porous material composed of organic ligands and metal centers with crystalline morphology, and has been developed as a promising class of new materials for high-efficiency HER electrocatalysts. In this review, the progress and current developments of various transition metal MOFs and MOF-derived electrocatalysts for HER are summarized. The application of MOF-derived materials in HER is documented in detail. The reasons why the original MOF materials show good HER activity but poor stability are discussed. The effect of bimetal-doped and heteroatom-doped MOF-derived materials on catalytic activity and stability is highlighted. The understandings of the synergy between metal center and heteroatoms are provided. The general principle of HER in acidic and alkaline electrolytes is introduced. The application and future prospects of MOF-derived materials in HER catalysts are presented.

Magnetic nanomaterials show promising applications in heterogeneous catalysis because of their ease of separation and good reusability. The magnetization saturation values of magnetic nanoparticles...

Rational design of highly active and durable electrocatalysts for oxygen reduction reaction is critical to substitute precious metal platinum for fuel cells. Herein, a novel non-precious atomic scandium embedded into nitrogen-doped graphene material is successfully synthesized via a facile annealing method. The catalyst exhibits superior oxygen reduction reaction performance in both 0.1 M KOH and 0.5 M H2SO4, with onset potential (Eonset, 0.99 vs 0.82 V) and half-wave potential (E1/2, 0.89 vs 0.72 V). Theoretical calculations reveal that the possible active sites for ORR might be ScN3O and ScN2O embedded into the N-doped graphene. The outstanding electrochemical stability and strong tolerance to methanol crossover on the atomic scandium and nitrogen-codoped graphene make it a promising application in metal-air batteries and fuel cells.