Catalyst overcoating engineering towards high-performance electrocatalysis

Clean and sustainable energy needs the development of advanced heterogeneous catalysts as they are of vital importance for electrochemical transformation reactions in renewable energy conversion and storage devices. Advances in nanoscience and material chemistry have afforded great opportunities for the design and optimization of nanostructured electrocatalysts with high efficiency and practical durability. In this review article, we specifically emphasize the synthetic methodologies for the versatile surface overcoating engineering reported to date for optimal electrocatalysts. We discuss the recent progress in the development of surface overcoating-derived electrocatalysts potentially applied in polymer electrolyte fuel cells and water electrolyzers by correlating catalyst intrinsic structures with electrocatalytic properties. Finally, we present the opportunities and perspectives of surface overcoating engineering for the design of advanced (electro)catalysts and their deep exploitation in a broad scope of applications.

Emergence of Ni-Based Chalcogenides (S and Se) for Clean Energy Conversion and Storage

Nickel chalcogenide (S and Se) based nanostructures intrigued scientists for some time as materials for energy conversion and storage systems. Interest in these materials is due to their good electrochemical stability, eco-friendly nature, and low cost. The present review compiles recent progress in the area of nickel-(S and Se)-based materials by providing a comprehensive summary of their structural and chemical features and performance. Improving properties of the materials, such as electrical conductivity and surface characteristics (surface area and morphology), through strategies like nano-structuring and hybridization, are systematically discussed. The interaction of the materials with electrolytes, other electro-active materials, and inactive components are analyzed to understand their effects on the performance of energy conversion and storage devices. Finally, outstanding challenges and possible solutions are briefly presented with some perspectives toward the future development of these materials for energy-oriented devices with high performance.

Designing Zn-doped nickel sulfide catalysts with an optimized electronic structure for enhanced hydrogen evolution reaction

Designing non-noble-metal electrocatalysts with excellent performance and economic benefits toward the hydrogen evolution reaction (HER) is extremely crucial for future energy development. In particular, the rational cationic-doped strategy can effectively tailor the electronic structure of the catalysts and improve the free energy of the adsorbed intermediate, thus enhancing HER performance. Herein we reported Zn-doped Ni₃S₂ nanosheet arrays supported on Ni foam (Zn-Ni₃S₂/NF) that were synthesized by a two-step hydrothermal process for improving HER catalysis under alkaline conditions. Remarkably, the obtained Zn-Ni₃S₂/NF displays excellent HER catalytic performance with an overpotential of 78 mV to reach a current density of 10 mA cm^-2 and dramatic long-term stability for 18 h in 1 M KOH. In addition, the results based on the density functional theory calculations reveal that Zn dopants can modulate the electronic structure of Ni₃S₂ and optimize the hydrogen adsorption free energy (ΔG_H*). Thus cationic-doping engineering provides an efficient method to enhance the intrinsic activities of transition-metal sulfides, which may contribute to the development of nonprecious electrocatalysts for HER.

Boosting the efficiency and stability of CoMoS4 by N incorporation for electrocatalytic hydrogen evolution

Here, an in situ N incorporation method was developed to boost the efficiency and durability of CoMoS₄ electrocatalyst for hydrogen evolution. Theoretical and experimental results reveal that such modification not only reduces the energy barrier of H* desorption by decreasing the electron densities around active metal sites, but also decreases the leaching rates of the metal ions with enhanced stability.

Morphologically controlled cobalt oxide nanoparticles for efficient oxygen evolution reaction

Electrochemical water oxidation is one of the thrust areas of research today in solving energy and environmental issues. The morphological control in the synthesis of nanomaterials plays a crucial role in designing efficient electrocatalyst. In general, various synthetic parameters can direct the morphology of nanomaterials and often this is the main driving force for the electrocatalyst in tuning the rate of the oxygen evolution reaction (OER) for the electrochemical water-splitting. Here, a facile and cost-effective synthesis of spinel cobalt oxides (Co₃O₄) via a one-pot hydrothermal pathway with tunable morphology has been demonstrated. Different kinds of morphologies have been obtained by systematically varying the reaction time i.e. nanospheres, hexagon and nanocubes. Their catalytic activity has been explored towards OER in 1.0 M alkaline KOH solution. The catalyst Co₃O₄-24 h nanoparticles synthesized in 24 h reaction time shows the lowest overpotential (η) value of 296 mV at 10 mA cm^-2 current density, in comparison to that of other as-prepared catalysts i.e. Co₃O₄-pH9 (311 mV), Co₃O₄-12 h (337 mV), and Co₃O₄-6 h (342 mV) with reference to commercially available IrO₂ (415 mV). Moreover, Co₃O₄-24 h sample shows the outstanding electrochemical stability up to 25 h time.

Formation of graphene encapsulated cobalt–iron phosphide nanoneedles as an attractive electrocatalyst for overall water splitting

Hierarchical CoFe–P nanoneedles encapsulated in the graphene texture are fabricated for water splitting applications.

Al-doped nickel sulfide nanosheet arrays as highly efficient bifunctional electrocatalysts for overall water splitting

The development of low-cost, high-activity, durable non-precious metal bifunctional electrocatalysts is of great importance in the production of hydrogen by water electrolysis. In this work, we have prepared new Al-doped Ni₃S₂ nanosheet arrays grown on Ni foam (Al-Ni₃S₂/NF) as an excellent bifunctional electrocatalyst in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The Al-Ni₃S₂/NF electrode obtained only requires extremely low overpotentials of 86 and 223 mV for the HER and OER to achieve a current density of 10 mA cm^-2 in 1 M KOH, respectively. Moreover, the electrolytic cell assembled using this electrode as both cathode and anode provides a current density of 10 mA cm^-2 at an extremely low battery voltage of 1.58 V relative to that with Ni₃S₂/NF (1.71 V). Additionally, both experimental results and theoretical calculations reveal that the increased electrochemical active surface area and optimized intermediate adsorption free energies are responsible for the enhanced electrocatalytic performance. This work provides a promising bifunctional electrocatalyst for water electrolysis in alkaline media with broad application prospects.

Different phases of few-layer MoS2 and their silver/gold nanocomposites for efficient hydrogen evolution reaction

Three different 1T phase contents of MoS₂ were synthesized; the electrocatalytic performances of their silver/gold nanocomposites toward the HER were investigated.

Performance enhancement of oxygen evolution reaction through incorporating bimetallic electrocatalysts in two-dimensional metal–organic frameworks

We designed and synthesized a series of bimetallic and monometallic 2D metal–organic framework electrocatalysts with excellent stability, discussing their different electrochemical catalysts for oxygen evolution reaction (OER).

Adjustable anchoring of Ni/Co cations by oxygen-containing functional groups on functionalized graphite paper and accelerated mass/electron transfer for overall water splitting

NCS–NCO/FGP_0.44 with a cellular network of porous nanosheets and close-contact heterointerface reveals accelerated interfacial mass/electron transportation for overall water splitting.

P-doped nickel sulfide nanosheet arrays for alkaline overall water splitting

Heazlewoodite, Ni₃S₂, is one of the most promising bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media due to its metallic conductivity and low cost.

Self-supported CoFe LDH/Co0.85Se nanosheet arrays as efficient electrocatalysts for the oxygen evolution reaction

Self-supported binary hybrid heterogeneous CoFe LDH/Co_0.85Se nanosheet array catalyst for efficient oxygen evolution reaction.