Herein, we demonstrate the use of heterostructures comprised of Co/β-Mo2 C@N-CNT hybrids for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline electrolyte. The Co can not only create a well-defined heterointerface with β-Mo2 C but also overcomes the poor OER activity of β-Mo2 C, thus leading to enhanced electrocatalytic activity for HER and OER. DFT calculations further proved that cooperation between the N-CNTs, Co, and β-Mo2 C results in lower energy barriers of intermediates and thus greatly enhances the HER and OER performance. This study not only provides a simple strategy for the construction of heterostructures with nonprecious metals, but also provides in-depth insight into the HER and OER mechanism in alkaline solution.

Heterostructures Composed of N‑Doped Carbon Nanotubes Encapsulating Cobalt and β‑Mo 2 C Nanoparticles as Bifunctional Electrodes for Water Splitting

Nitrogen is a fundamental constituent for all living creatures on the Earth and modern industrial society. The current nitrogen industry is largely powered by fossil fuels with huge energy consumption and carbon dioxide emission, and nitrogen pollution in surface water bodies induced by the indiscriminate discharge of industrial and domestic wastewater has become a worldwide environmental concern. Electrochemical techniques for nitrogen fixation and transformation under mild conditions are promising approaches to meet the challenge of efficiently managing and balancing the nitrogen cycle, where the rational design of advanced electrocatalysts from both structural and compositional aspects down to the nanoscale plays the most essential role. Herein, important nitrogen species including dinitrogen (N2), ammonia (NH3) and hydrazine (N2H4), their transformation processes between each other including the nitrogen reduction reaction (NRR), ammonia oxidation reaction (AOR) and hydrazine oxidation reaction (HzOR), and research progress on the development of related electrocatalysts are systematically summarized, aiming at establishing a general picture of the whole nitrogen cycle instead of a certain single reaction. Strategies combining theoretical computations and experimental optimizations are proposed to improve the catalytic performance including activity, efficiency, selectivity and stability, finally contributing to a self-sufficient and carbon-free "green" nitrogen economy.

Electrochemical nitrogen fixation and utilization: theories, advanced catalyst materials and system design.

The hydrogen evolution reaction (HER) is a half-cell reaction in water electrolysis for producing hydrogen gas. In industrial water electrolysis, the HER is often conducted in alkaline media to achieve higher stability of the electrode materials. However, the kinetics of the HER in alkaline medium is slow relative to that in acid because of the low concentration of protons in the former. Under the latter conditions, the entire HER process will require additional effort to obtain protons by water dissociation near or on the catalyst surface. Heterostructured catalysts, with fascinating synergistic effects derived from their heterogeneous interfaces, can provide multiple functional sites for the overall reaction process. At present, the activity of the most active known heterostructured catalysts surpasses (platinum-based heterostructures) or approaches (noble-metal-free heterostructures) that of the commercial Pt/C catalyst under alkaline conditions, demonstrating an infusive potential to break through the bottlenecks. This review summarizes the most representative and recent heterostructured HER catalysts for alkaline medium. The basics and principles of the HER under alkaline conditions are first introduced, followed by a discussion of the latest advances in heterostructured catalysts with/without noble-metal-based heterostructures. Special focus is placed on approaches for enhancing the reaction rate by accelerating the Volmer step. This review aims to provide an overview of the current developments in alkaline HER catalysts, as well as the design principles for the future development of heterostructured nano- or micro-sized electrocatalysts.

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Heterostructured Electrocatalysts for Hydrogen Evolution Reaction Under Alkaline Conditions

Metal-organic frameworks derived reverse-encapsulation Co-NC@Mo2C complex for efficient overall water splitting

Hydrogen production by electrocatalytic water splitting is an efficient and economical technology, however, is severely impeded by the kinetic-sluggish and low value-added anodic oxygen evolution reaction. Here we report the nickel-molybdenum-nitride nanoplates loaded on carbon fiber cloth (Ni-Mo-N/CFC), for the concurrent electrolytic productions of high-purity hydrogen at the cathode and value-added formate at the anode in low-cost alkaline glycerol solutions. Especially, when equipped with Ni-Mo-N/CFC at both anode and cathode, the established electrolyzer requires as low as 1.36 V of cell voltage to achieve 10 mA cm−2, which is 260 mV lower than that in alkaline aqueous solution. Moreover, high Faraday efficiencies of 99.7% for H2 evolution and 95.0% for formate production have been obtained. Based on the excellent electrochemical performances of Ni-Mo-N/CFC, electrolytic H2 and formate productions from the alkaline glycerol solutions are an energy-efficient and promising technology for the renewable and clean energy supply in the future. Hydrogen production by electrocatalytic water splitting is limited by the sluggish evolution kinetics of low value-oxygen. Here, authors show concurrent electrolytic productions of H2 and glycerol oxidation to formate by utilizing Ni-Mo-N/CFC electro-catalyst as both anodic and cathodic catalysts.

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Nickel-molybdenum nitride nanoplate electrocatalysts for concurrent electrolytic hydrogen and formate productions.

Water electrolysis is a promising source of hydrogen; however, technological challenges remain. Intensive efforts have focused on developing highly efficient and earth-abundant electrocatalysts for water splitting. An effective strategy is proposed, using a bifunctional tubular cobalt perselenide nanosheet electrode, in which the sluggish oxygen evolution reaction is substituted with anodic hydrazine oxidation so as to assist energy-efficient hydrogen production. Specifically, this electrode produces a current density of 10 mA cm-2 at -84 mV for hydrogen evolution and -17 mV for hydrazine oxidation in 1.0 m KOH and 0.5 m hydrazine electrolyte. An ultralow cell voltage of only 164 mV is required to generate a current density of 10 mA cm-2 for 14 hours of stable water electrolysis.

Anodic Hydrazine Oxidation Assists Energy-Efficient Hydrogen Evolution over a Bifunctional Cobalt Perselenide Nanosheet Electrode

Tailoring the size, controlling the morphology, and designing the metal–organic interface are three promising strategies to improve the catalytic performance of monometallic noble-metal nanocrystals. In the “hydrogen economy” society, water electrolysis is viewed as one of the most promising technologies for hydrogen production. The design and synthesis of highly active and durable electrocatalysts for the hydrogen evolution reaction (HER) is vitally important for the development of the hydrogen economy. In this work, we successfully synthesized polyallylamine (PAA)-functionalized Pt tripods (Pttripods@PAA) with ultrathin and ultralong branches through a facile chemical reduction method in an aqueous solution of PAA. The morphology, structure, and composition of Pttripods@PAA were fully investigated by various physical techniques. The characterization results reveal that ultrathin and ultralong branches of Pttripods@PAA have a concave structure with high-index facets and that PAA strongly binds on the Pt ...

Polyallylamine-Functionalized Platinum Tripods: Enhancement of Hydrogen Evolution Reaction by Proton Carriers

Optimizing the shape, structure, and interface of noble metal bimetallic nanostructures significantly improves their catalytic properties. Recently, Au@Pd core–shell bimetallic nanostructures have ...

Au Nanowires@Pd-Polyethylenimine Nanohybrids as Highly Active and Methanol-Tolerant Electrocatalysts toward Oxygen Reduction Reaction in Alkaline Media

Au core-PtAu alloy shell nanowires for formic acid electrolysis

Heterostructured noble metal/transition metal nanohybrids have attracted increasing attention in energy/environment-related electrocatalysis field due to their high activity. In this work, the ultrathin NiO nanosheets (NiO-NSs) decorated with ultrafine Rh nanocrystals (Rh-NCs) electrocatalyst (termed as Rh-NCs/NiO-NSs) is successfully synthesized by using mixed-cyanogels-NaBH4 method and succedent heat treatment. Physical characterizations confirm that as-prepared Rh-NCs/NiO-NSs have 1.6 nm thickness and a large specific surface area of 166.2 m2 g−1, and ultrafine Rh-NCs are uniformly dispersed on surface of NiO-NSs. Electrochemical measurements show that the incorporation of Rh-NCs can promote the generation of NiIIIOOH species and accelerate the oxidation of CO, thus significantly improving the electrocatalytic performance of NiO-NSs for urea electro-oxidation reaction (UEOR). The UEOR current at Rh-NCs/NiO-NSs achieves the 616 mA mg−1 at 1.55 V potential, which is 11.5 times bigger than that at NiO-NSs in 1 M KOH solution with 0.33 M urea. Additionally, Rh-NCs/NiO-NSs also show excellent long-term stability due to improved structural/chemical stability and anti-poisoning capability.

Yu Chen

Papers

Anodic Hydrazine Oxidation Assists Energy-Efficient Hydrogen Evolution over a Bifunctional Cobalt Perselenide Nanosheet Electrode

Polyallylamine-Functionalized Platinum Tripods: Enhancement of Hydrogen Evolution Reaction by Proton Carriers

Au Nanowires@Pd-Polyethylenimine Nanohybrids as Highly Active and Methanol-Tolerant Electrocatalysts toward Oxygen Reduction Reaction in Alkaline Media

Au core-PtAu alloy shell nanowires for formic acid electrolysis

Ultrafine Rh nanocrystals decorated ultrathin NiO nanosheets for urea electro-oxidation