Interface engineering of hierarchical NiCoP/NiCoSx heterostructure arrays for efficient alkaline hydrogen evolution at large current density

Design of NiCoP nanorod loaded on cocoon carbon substrate and its non-metal doping for efficient hydrogen evolution

The quest for effective and sustainable electrocatalysts for hydrogen evolution is crucial in advancing the widespread use of H2. In this study, we utilized silkworm cocoons as the source material to produce porous N-doped carbon (PNCC) substrates through a process involving degumming and annealing. Subsequently, NiCoP nanorod (NiCoP@PNCC) is deposited onto the substrates via a simple impregnation and calcination method to enhance the catalytic performance for the hydrogen evolution reaction (HER). The optimal spacing between the silk fibers of PNCC facilitates longitudinal growth, increases the active surface area, and balances the adsorption and desorption of reaction intermediates, thereby accelerating HER kinetics. Consequently, NiCoP@PNCC demonstrates impressive performance, with 44 mV overpotential to achieve a current density of 10 mA cm-2. Additionally, density functional theory (DFT) calculations reveal that the electronic structure and energy band of NiCoP@PNCC can be modified through the doping of elements such as B, C, N, O, F, and S. In addition, with the electronegativity enhancement of the doping elements, the interaction between Co atoms in NiCoP@PNCC and O atoms in adsorbed H2O molecules gradually enhanced, which is conducive to the dissociation of water in alkaline solution. This research introduces a novel approach for fine-tuning the catalytic activity of transition metal phosphides.

Accelerated water dissociation kinetics by nickel-nickelous hydroxide epitaxial interfaces for superior alkaline hydrogen generation

The intrinsic performance of an electrocatalyst can be reinforced by constructing appropriate epitaxial interfaces, where the modulated electronic states and adsorption/desorption behaviors are conductive to enhancing electrocatalytic activity. Herein, nickel-nickelous hydroxide epitaxial interface supported on nickel foam (Ni-Ni(OH)2/NF) with epitaxial growth of nickel nanoparticles on the surface of nickelous hydroxide nanoribbons is devised for alkaline hydrogen evolution reaction (HER). Notably, the Ni-Ni(OH)2/NF reveals excellent electrocatalytic activity of alkaline HER (158 mV @ 100 mA cm-2), along with robust stability (90 % activity retention after 150 h continuous test at 200 mA cm-2). Theoretical simulations disclose the tuned interface electronic structure and accelerated water dissociation around the epitaxial nickel-nickelous hydroxide interface result in efficient electrochemical activity toward alkaline hydrogen evolution.

Synthesis and Electrocatalytic Applications of Layer-Structured Metal Chalcogenides Composites

Featured with the attractive properties such as large surface area, unique atomic layer thickness, excellent electronic conductivity, and superior catalytic activity, layered metal chalcogenides (LMCs) have received considerable research attention in electrocatalytic applications. In this review, the approaches developed to synthesize LMCs-based electrocatalysts are summarized. Recent progress in LMCs-based composites for electrochemical energy conversion applications including oxygen reduction reaction, carbon dioxide reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, overall water splitting, and nitrogen reduction reaction is reviewed, and the potential opportunities and practical obstacles for the development of LMCs-based composites as high-performing active substances for electrocatalytic applications are also discussed. This review may provide an inspiring guidance for developing high-performance LMCs for electrochemical energy conversion applications.

Ru nanoclusters anchored on boron- and nitrogen-doped carbon for a highly efficient hydrogen evolution reaction in alkaline seawater

Electrochemical seawater splitting is an intriguing strategy for green hydrogen production. Constructing advanced electrocatalysts for the hydrogen evolution reaction (HER) in seawater is extremely demanded for accelerating the sluggish kinetic process. Herein, a Ru nanocluster anchored on boron- and nitrogen-doped carbon (Ru/NBC) catalyst was successfully synthesized for the HER in alkaline/seawater electrolytes. Remarkably, Ru/NBC exhibits outstanding activity and durability, delivering low overpotentials@10 mA cm-2 in 1.0 M KOH (30 mV) and 1.0 M KOH + seawater electrolyte (35 mV), outperforming Pt/C, Ru/NC, Ru/BC and Ru/C. Additionally, Ru/NBC also provides a high specific activity of 0.093 mA cm-2ECSA at an overpotential of 150 mV, which is higher than those of Ru/NC, Ru/BC and Ru/C, respectively. Density functional theory calculation results demonstrate that the Ru-B formed interfacial chemical bond can regulate the electronic structure of Ru active sites of Ru/NBC, which can facilitate the adsorption of water and hydrogen in alkaline media. This work provides a feasible strategy to fabricate outstanding electrocatalysts for the HER in alkaline/alkaline seawater electrolytes.

Non-precious metal-based heterostructure catalysts for hydrogen evolution reaction: mechanisms, design principles, and future prospects

As a highly promising clean energy source to replace fossil fuels in the 21st century, hydrogen energy has garnered considerable attention, with water electrolysis emerging as a key hydrogen production technology. The development of highly active and stable non-precious metal-based catalysts for the hydrogen evolution reaction (HER) is crucial for achieving efficient and low-cost hydrogen production through electrolysis. Recently, heterostructure composite catalysts comprising two or more non-precious metals have demonstrated outstanding catalytic performance. First, we introduced the basic mechanism of the HER and, based on the reported HER theory, discussed the essence of constructing heterostructures to improve the catalytic activity of non-noble metal-based catalysts, that is, the coupling effect between components effectively regulates the electronic structure and the position of d-band centers. Then three catalytic effects of non-precious metal-based heterogeneous catalysts are described: synergistic effect, electron transfer effect and support effect. Lastly, we emphasized the potential of non-precious metal-based heterogeneous catalysts to replace precious metal-based catalysts, and summarized the future prospects and challenges.

Construct of an Electrodeposited Cobalt-Molybdenum Film and Evaluation of Its Efficiency in Hydrogen Evolution

Hydrogen is a valuable clean energy source, and electrolysis to produce hydrogen from water is a crucial component. However, a major problem of hydrogen generation by electrolysis is its large overpotential and poor economics. To reduce the overpotential, we mainly use nickel foam and Co-Mo ions as feedstock and create an efficient catalytic material by electrodeposition. The Co-Mo interaction improves the current efficiency. In 1 mol/L NaOH solution, the overpotential of the Co-Mo-NF composites was low when the current density is -10 mA/cm², with the best value reaching 45.3 mV, which is less than those of Co-NF (94.4 mV) and Mo-NF (88.2 mV). All deposits had similar Tafel slopes in the 77.9 mV/decade range. The catalyst does not just have a favorable effect on hydrogen formation but also has a surprisingly high double-layer capacitance (up to 180 mF/cm²) and good stability. This research provides an impactful approach for developing a non-precious metal HER catalyst for industrial hydrogen production.

Tailored nitrogen-defect induced by diels-alder reaction for enhanced electrochemical hydrogen evolution reaction

Electrocatalytic water splitting in an alkaline medium is recognized as the promising technology to sustainably generate clean hydrogen energy via hydrogen evolution reaction (HER), while the sluggish water dissociation and subsequent *H adsorption steps greatly retarded the reaction kinetics and efficiency of the overall hydrogen evolution process. Whilst nitrogen (N)-doped carbon-based materials are attractive candidates for promoting HER activity, the facile fabrication and gaining a deeper insight into the electrocatalytic mechanism are still challenging. Herein, inspired by the Diels-Alder reaction, we precisely tailored six-membered pyridinic N and five-membered pyrrolic N sites at the edge of the carbon substrates. Comprehensive analysis validates that the participation of pyridinic N (electron-withdrawing) and pyrrolic N (electron-releasing) will induce the charge rearrangements, and further generate local electrophilic and nucleophilic domains in adjacent carbon rings, which guarantees the occurrence of water dissociation to generate protons and the subsequent adsorption of *H intermediates through electrostatic interactions, thereby facilitating the overall reaction kinetics. To this end, the optimal NC-ZnCl₂-25 % electrocatalysts present excellent alkaline HER activity (η₁₀ = 45 mV, Tafel slop of 37.7 mV dec^-1) superior to commercial Pt/C.

Hydrogen Evolution Reaction Performance of Ni-Co-Coated Graphene-Based 3D Printed Electrodes

Additive manufacturing has been a very promising topic in recent years for research and development studies and industrial applications. Its electrochemical applications are very popular due to the cost-effective rapid production from the environmentally friendly method. In this study, three-dimensional (3D) printed electrodes are prepared by Ni and Co coatings in different molar ratios. Different Ni/Co molar ratios (x:y) of the Ni/Co/x:y alloys are prepared as 1:1, 1:4, and 4:1 and they are named Ni/Co/1:1, Ni/Co/4:1, and Ni/Co/1:4, respectively. According to the results, when the 3D electrode samples are coated with Ni and Co at different molar ratios, the kinetic performance of the NiCo-coated 3D electrode samples for hydrogen evolution reaction is enhanced compared to that of the uncoated 3D electrode sample. The results indicate that the Ni/Co/1:4-coated 3D electrode has the highest kinetic activity for hydrogen evolution reactions (HERs). The calculated Tafel's slope and overpotential value (η₁₀) for HER are determined as 164.65 mV/dec and 101.92 mV, respectively. Moreover, the Ni/Co/1:4-coated 3D electrode has an 81.2% higher current density than the other electrode. It is observed that the 3D printing of the electrochemical electrodes is very promising when they are coated with Ni-Co metals in different ratios. This study provides a new perspective on the use of 3D printed electrodes for high-performance water electrolysis.