The development of low‐cost, high‐efficiency, and robust electrocatalysts for the oxygen evolution reaction (OER) is urgently needed to address the energy crisis. In recent years, ...non‐noble‐metal‐based OER electrocatalysts have attracted tremendous research attention. Beginning with the introduction of some evaluation criteria for the OER, the current OER electrocatalysts are reviewed, with the classification of metals/alloys, oxides, hydroxides, chalcogenides, phosphides, phosphates/borates, and other compounds, along with their advantages and shortcomings. The current knowledge of the reaction mechanisms and practical applications of the OER is also summarized for developing more efficient OER electrocatalysts. Finally, the current states, challenges, and some perspectives for non‐noble‐metal‐based OER electrocatalysts are discussed.
This review summarizes the evaluation criteria, recent advancements of non‐noble‐metal‐based electrocatalysts, reaction mechanisms, and some practical applications of the oxygen evolution reaction (OER). Although great strides have been made in the past decades, the current state of non‐noble‐metal‐based OER electrocatalysts is still facing many challenges, which are discussed together with some useful perspectives and future directions.
Modulation of the electronic structure of metal catalysts is an effective approach to optimize the electrocatalytic activity. Herein, we show a surprisingly strong activation effect of black ...phosphorus (BP) on platinum (Pt) catalysts to give greatly enhanced catalytic activity in the hydrogen evolution reaction (HER). The unique and negative binding energy between BP and Pt leads to spontaneous formation of Pt‐P bonds producing strong synergistic ligand effects on the Pt nanoparticles. No Pt‐P bonds are formed with red phosphorus which is another allotrope of P. By controlling the number of Pt‐P bonds, 3.5‐fold enhancement in the HER activity can be achieved from the BP‐activated Pt catalyst and the activity is 6.1 times higher than that of the state‐of‐the‐art commercial Pt/C catalyst. The BP‐activated Pt catalyst exhibits a current density of 82.89 mA cm−2 with only 1 μg of Pt in 1 m KOH at an overpotential of 70 mV.
Back in black: Surprisingly strong activation effects of black phosphorus (BP) on Pt catalysts and subsequent modulation the surface electronic structure of Pt result in greatly enhanced catalytic activity in the hydrogen evolution reaction (HER).
In view of the clean and sustainable energy, metal–organic frameworks (MOFs) based materials, including pristine MOFs, MOF composites, and their derivatives are emerging as unique electrocatalysts ...for oxygen reduction reaction (ORR). Thanks to their tunable compositions and diverse structures, efficient MOF‐based materials provide new opportunities to accelerate the sluggish ORR at the cathode in fuel cells and metal–air batteries. This Minireview first provides some introduction of ORR and MOFs, followed by the classification of MOF‐based electrocatalysts towards ORR. Recent breakthroughs in engineering MOF‐based ORR electrocatalysts are highlighted with an emphasis on synthesis strategy, component, morphology, structure, electrocatalytic performance, and reaction mechanism. Finally, some current challenges and future perspectives for MOF‐based ORR electrocatalysts are also discussed.
Despite the rapid developments in the past decade, many great challenges remain for the practical use of metal–organic frameworks (MOFs) based electrocatalysts. This Minireview summaries some major recent research efforts and advances on MOF‐based electrocatalysts for the oxygen reduction reaction. Some promising directions and strategies are also discussed.
Nitrate electrocatalytic reduction (NO3RR) for ammonia production is a promising strategy to close the N‐cycle from nitration contamination, as well as an alternative to the Haber–Bosch process with ...less energy consumption and carbon dioxide release. However, current long‐term stability of NO3RR catalysts is usually tens of hours, far from the requirements for industrialization. Here, symmetry‐broken Cusingle‐atom catalysts are designed, and the catalytic activity is retained after operation for more than 2000 h, while an average ammonia production rate of 27.84 mg h−1 cm−2 at an industrial level current density of 366 mA cm−2 is achieved, obtaining a good balance between catalytic activity and long‐term stability. Coordination symmetry breaking is achieved by embedding one Cu atom in graphene nanosheets with two N and two O atoms in the cis‐configuration, effectively lowering the coordination symmetry, rendering the active site more polar, and accumulating more NO3− near the electrocatalyst surface. Additionally, the cis‐coordination splits the Cu 3d orbitals, which generates an orbital‐symmetry‐matched π‐complex of the key intermediate *ONH and reduces the energy barrier, compared with the σ‐complex generated with other catalysts. These results reveal the critical role of coordination symmetry in single‐atom catalysts, prompting the design of more coordination‐symmetry‐broken electrocatalysts toward possible industrialization.
A coordination‐symmetry‐breaking Cusingle‐atom catalyst enables a good balance between catalytic activity and long‐term stability in nitrate electroreduction to ammonia. The catalytic activity is retained after operation for more than 2000 h, while an average ammonia production rate of 27.84 mg h−1 cm−2 at an industrial level current density of 366 mA cm−2 is achieved.
Electrocatalysts based on hierarchically structured and heteroatom‐doped non‐noble metal oxide materials are of great importance for efficient and low‐cost electrochemical water splitting systems. ...Herein, the synthesis of a series of hierarchical hollow nanoplates (NPs) composed of ultrathin Co3O4 nanosheets doped with 13 different metal atoms is reported. The synthesis involves a cooperative etching−coordination−reorganization approach starting from zeolitic imidazolate framework‐67 (ZIF‐67) NPs. First, metal atom decorated ZIF‐67 NPs with unique cross‐channels are formed through a Lewis acid etching and metal species coordination process. Afterward, the composite NPs are converted to hollow Co3O4 hierarchical NPs composed of ultrathin nanosheets through a solvothermal reaction, during which the guest metal species is doped into the octahedral sites of Co3O4. Density functional theory calculations suggest that doping of small amount of Fe atoms near the surface of Co3O4 can greatly enhance the electrocatalytic activity toward the oxygen evolution reaction (OER). Benefiting from the structural and compositional advantages, the obtained Fe‐doped Co3O4 hierarchical NPs manifest superior electrocatalytic performance for OER with an overpotential of 262 mV at 10 mA cm−2, a Tafel slope of 43 mV dec−1, and excellent stability even at a high current density of 100 mA cm−2 for 50 h.
Metal‐atom‐doped Co3O4 hierarchical nanoplates constructed by ultrathin nanosheets are synthesized by a cooperative etching−coordination−reorganization approach. The method allows doping of 13 metal elements in total. With its structural and compositional advantages, as an example, the Fe‐doped Co3O4 hierarchical nanoplates exhibit greatly enhanced electrocatalytic performance for oxygen evolution.
Efficient electrocatalysts are of great importance in improving the water splitting efficiency. Herein, we develop a self-templating strategy to construct porous iron cobalt (oxy)phosphide (Fe-Co-P) ...nanoboxes as promising pre-catalysts for the oxygen evolution reaction in alkaline solution. The constructed Fe-Co-P nanoboxes exhibit excellent electrocatalytic activity and afford a current density of 10 mA cm
−2
at a small overpotential of 269 mV. Moreover, the structural evolution of the metal phosphides in the oxygen evolution process has been well monitored. X-ray absorption near-edge structure analyses and computational studies reveal that the structural merits and the effective intramolecular electronic coupling between the Fe and Co atoms
via
P/O bridges are responsible for the greatly improved electrocatalytic activity.
The effective intramolecular electronic coupling between the Fe and Co atoms
via
P/O bridges greatly enhances the electrocatalytic activity of Fe-Co (oxy)phosphide nanoboxes.
PdCo nanotube arrays (NTAs) supported on carbon fiber cloth (CFC) (PdCo NTAs/CFC) are presented as high‐performance flexible electrocatalysts for ethanol oxidation. The fabricated flexible PdCo ...NTAs/CFC exhibits significantly improved electrocatalytic activity and durability compared with Pd NTAs/CFC and commercial Pd/C catalysts. Most importantly, the PdCo NTAs/CFC shows excellent flexibility and the high electrocatalytic performance remains almost constant under the different distorted states, such as normal, bending, and twisting states. This work shows the first example of Pd‐based alloy NTAs supported on CFC as high‐performance flexible electrocatalysts for ethanol oxidation.
PdCo nanotube arrays supported on carbon fiber cloth for use as high‐performance electrocatalysts were synthesized for ethanol electrooxidation. The system of nanotube arrays on carbon fiber cloth is highly flexible, and its high electrocatalytic performance is almost constant regardless of the distorted state, such as normal, bent, and twisted.
The development of efficient and low‐cost electrocatalysts toward the oxygen evolution reaction (OER) is critical for improving the efficiency of several electrochemical energy conversion and storage ...devices. Here, we report an elaborate design and synthesis of porous Co‐based trimetallic spinel oxide nanoboxes (NiCo2−xFexO4 NBs) by a novel metal‐organic framework engaged strategy, which involves chemical etching, cation exchange, and subsequent thermal oxidation processes. Owing to the structural and compositional advantages, the optimized trimetallic NiCo2−xFexO4 NBs (x is about 0.117) deliver superior electrocatalytic performance for OER with an overpotential of 274 mV at 10 mA cm−2, a small Tafel slope of 42 mV dec−1, and good stability in alkaline electrolyte, which is much better than that of Co‐based bi/monometallic spinel oxides and even commercial RuO2.
Co‐based trimetallic spinel oxide nanoboxes are synthesized through an elaborate strategy involving chemical etching, cation exchange and thermal oxidation processes. The unique structural and compositional advantages endow the trimetallic NiCo2−xFexO4 nanoboxes with superior electrocatalytic activity and stability toward oxygen evolution reaction.
Delicate design of nanostructures for oxygen‐evolution electrocatalysts is an important strategy for accelerating the reaction kinetics of water splitting. In this work, Ni–Fe ...layered‐double‐hydroxide (LDH) nanocages with tunable shells are synthesized via a facile one‐pot self‐templating method. The number of shells can be precisely controlled by regulating the template etching at the interface. Benefiting from the double‐shelled structure with large electroactive surface area and optimized chemical composition, the hierarchical Ni–Fe LDH nanocages exhibit appealing electrocatalytic activity for the oxygen evolution reaction in alkaline electrolyte. Particularly, double‐shelled Ni–Fe LDH nanocages can achieve a current density of 20 mA cm−2 at a low overpotential of 246 mV with excellent stability.
Hierarchical Ni–Fe layered‐double‐hy‐droxide (LDH) nanocages with different shells are designed and synthesized via a one‐pot self‐templating method. Benefiting from the optimized architecture and improved reaction kinetics, the double‐shelled Ni–Fe LDH nanocages demonstrate appealing electrocatalytic activity for the oxygen evolution reaction in an alkaline medium.
Photocatalysts with well‐designed compositions and structures are desirable for achieving highly efficient solar‐to‐chemical energy conversion. Heterostructured semiconductor photocatalysts with ...advanced hollow structures possess beneficial features for promoting the activity towards photocatalytic reactions. Here we develop a facile synthetic strategy for the fabrication of Fe2TiO5–TiO2 nanocages (NCs) as anode materials in photoelectrochemical (PEC) water splitting cells. A hydrothermal reaction is performed to transform MIL‐125(Ti) nanodisks (NDs) to Ti–Fe–O NCs, which are further converted to Fe2TiO5–TiO2 NCs through a post annealing process. Owing to the compositional and structural advantages, the heterostructured Fe2TiO5–TiO2 NCs show enhanced performance for PEC water oxidation compared with TiO2 NDs, Fe2TiO5 nanoparticles (NPs) and Fe2TiO5–TiO2 NPs.
Heterostructured Fe2TiO5–TiO2 nanocages are fabricated through a facile synthetic approach. With the advantages of the novel hollow heterostructure, the well‐defined FeTi2O5–TiO2 nanocages exhibit enhanced photoelectrochemical performance compared with TiO2 nanodisks, Fe2TiO5 nanoparticles, and Fe2TiO5–TiO2 nanoparticles.
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