Systematic Engineering on Ni-Based Nanocatalysts Effectively Promote Hydrogen Evolution Reaction

Rational Construction of Pt Incorporated Co3O4 as High-Performance Electrocatalyst for Hydrogen Evolution Reaction

Electrocatalysts in alkaline electrocatalytic water splitting are required to efficiently produce hydrogen while posing a challenge to show excellent performances. Herein, we have successfully synthesized platinum nanoparticles incorporated in a Co3O4 nanostructure (denoted as Pt-Co3O4) that show superior HER activity and stability in alkaline solutions (the overpotentials of 37 mV to reach 10 mA cm-2). The outstanding electrocatalytic activity originates from synergistic effects between Pt and Co3O4 and increased electron conduction. Theoretical calculations show a significant decrease in the ΔGH* of Co active sites and a remarkable increase in electron transport. Our work puts forward a special and simple synthesized way of adjusting the H* adsorption energy of an inert site for application in HER.

Nanoporous Nickel Cathode with an Electrostatic Chlorine-Resistant Surface for Industrial Seawater Electrolysis Hydrogen Production

Seawater electrolysis presents a promising avenue for green hydrogen production toward a carbon-free society. However, the electrode materials face significant challenges including severe chlorine-induced corrosion and high reaction overpotential, resulting in low energy conversion efficiency and low current density operation. Herein, we put forward a nanoporous nickel (npNi) cathode with high chlorine corrosion resistance for energy-efficient seawater electrolysis at industrial current densities (0.4-1 A cm-2). With the merits of an electrostatic chlorine-resistant surface, modulated Ni active sites, and a robust three-dimensional open structure, the npNi electrode showed a low hydrogen evolution reaction overpotential of 310 mV and a high electricity-hydrogen conversion efficiency of 59.7% at 400 mA cm-2 in real seawater and outperformed most Ni-based seawater electrolysis cathodes in recent publications and the commercial Ni foam electrode (459 mV, 46.4%) under the same test condition. In situ electrochemical impedance spectroscopy, high-frame-rate optical microscopy, and first-principles calculation revealed that the improved corrosion resistance, enhanced intrinsic activity, and mass transfer were responsible for the lowered electrocatalytic overpotential and enhanced energy efficiency.

Precisely Control Relationship between Sulfur Vacancy and H Absorption for Boosting Hydrogen Evolution Reaction

Effective and robust catalyst is the core of water splitting to produce hydrogen. Here, we report an anionic etching method to tailor the sulfur vacancy (VS) of NiS2 to further enhance the electrocatalytic performance for hydrogen evolution reaction (HER). With the VS concentration change from 2.4% to 8.5%, the H* adsorption strength on S sites changed and NiS2-VS 5.9% shows the most optimized H* adsorption for HER with an ultralow onset potential (68 mV) and has long-term stability for 100 h in 1 M KOH media. In situ attenuated-total-reflection Fourier transform infrared spectroscopy (ATR-FTIRS) measurements are usually used to monitor the adsorption of intermediates. The S- H* peak of the NiS2-VS 5.9% appears at a very low voltage, which is favorable for the HER in alkaline media. Density functional theory calculations also demonstrate the NiS2-VS 5.9% has the optimal |ΔGH*| of 0.17 eV. This work offers a simple and promising pathway to enhance catalytic activity via precise vacancies strategy.

Carbon nanotubes encapsulating Pt/MoN heterostructures for superior hydrogen evolution

Achieving efficient hydrogen evolution reaction (HER) catalysts to scale up electrochemical water splitting is desirable but remains a major challenge. Here, nitrogen-doped carbon nanotubes (NCNTs) loaded with PtNi/MoN electrocatalyst (PtNi/MoN@C) is synthesized by a simple strategy to obtain stronger interphase effects and significantly improve HER activity. The surface morphology of the materials is altered by Pt doping and the electronic structure of MoN is changed, which optimizing the electronic environment of the materials, shifting the binding energy and giving the materials a higher electrical conductivity, this ultimately leads to faster proton and electron transfer processes. The synergistic effect of Pt nanoparticles, MoN and the good combination with carbon leads to a high HER activity of 18 mV to reach 10 mA cm-2 in alkaline solution, outperforming that of the commercial Pt/C. Theoretical studies show that the heterostructures can efficiently enhance the electron transport and reduce the △GH*.

Metastable Hexagonal-Phase Nickel with Ultralow Pt Content for an Efficient Alkaline/Seawater Hydrogen Evolution Reaction

Hydrogen has been hailed as the core of the world's future energy architecture. It is imperative to develop catalysts with an efficient and sustained hydrogen evolution reaction (HER) to scale up alkaline/seawater electrolysis, yet significant difficulties and challenges, such as the high usage of precious metals, still remain. In this paper, a metastable-phase hexagonal close-packed (hcp) Ni-based catalyst with ultralow Pt content (3.1 at %) was designed, which has excellent catalytic performance in the alkaline/seawater HER. The optimal catalyst offers low overpotentials of 21 and 137 mV at 10 mA cm-2 and remains stable during operation for 100 and 300 h at this current density in 1.0 M KOH and real seawater, respectively. A mechanistic study shows that the metastable-phase Ni acts as an anchor site for OH-, which promotes the dissociation of water and greatly improves the formation rate of H2.

Electric double layer-mediated polarization field for optimizing photogenerated carrier dynamics and thermodynamics

Photocatalytic hydrogen evolution efficiency is limited due to unfavorable carrier dynamics and thermodynamic performance. Here, we propose to introduce electronegative molecules to build an electric double layer (EDL) to generate a polarization field instead of the traditional built-in electric field to improve carrier dynamics, and optimize the thermodynamics by regulating the chemical coordination of surface atoms. Based on theoretical simulation, we designed CuNi@EDL and applied it as the cocatalyst of semiconductor photocatalysts, finally achieved a hydrogen evolution rate of 249.6 mmol h^-1 g^-1 and remained stable after storing under environmental conditions for more than 300 days. The high H₂ yield is mainly due to the perfect work function, Fermi level and Gibbs free energy of hydrogen adsorption, improved light absorption ability, enhanced electron transfer dynamics, decreased HER overpotential and effective carrier transfer channel arose by EDL. Here, our work opens up new perspectives for the design and optimization of photosystems.

NiMo solid-solution alloy porous nanofiber as outstanding hydrogen evolution electrocatalyst

Developing a high-efficiency hydrogen evolution reaction (HER) electrocatalyst for the large-scale production of hydrogen is essential but challenging. In this study, we used NiMo solid-solution alloy porous nanofibers to develop a robust HER electrocatalyst through electrospinning, oxidization, and high-temperature reduction treatment. In 1 M KOH electrolyte, the fabricated NiMo solid-solution alloy porous nanofibers exhibited higher HER activity than Ni nanofibers, which required a low overpotential of 69, 208, and 300 mV at 100, 500, and 1000 mA cm^-2, respectively, and had outstanding durability at 100 mA cm^-2 over 60 h. We developed a promising candidate for a high-efficiency HER electrocatalyst, and our findings provided valuable information for fabricating highly robust alloy-based electrocatalysts.

IrPd Nanoalloy-Structured Bifunctional Electrocatalyst for Efficient and pH-Universal Water Splitting

The lack of high efficiency and pH-universal bifunctional electrocatalysts for water splitting to hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) hinders the large-scale production of green hydrogen. Here, an IrPd electrocatalyst supported on ketjenblack that exhibits outstanding bifunctional performance for both HER and OER at wide pH conditions is presented. The optimized IrPd catalyst exhibits a specific activity of 4.46 and 3.98 A mg_Ir ^-1 in the overpotential of 100 and 370 mV for HER and OER, respectively, in alkaline conditions. When applied to the anion exchange membrane electrolyzer, the Ir₄₄ Pd₅₆ /KB catalyst shows a stability of >20 h at a current of 250 mA cm^-2 for water decomposition, indicating promising prospects for practical applications. Beyond offering an advanced electrocatalyst, this work also guides the rational design of desirable bifunctional electrocatalysts for HER and OER by regulating the microenvironments and electronic structures of metal catalytic sites for diverse catalysis.

Homogenous Cr and C Doped 3D Self-Supporting NiO Cellular Nanospheres for Hydrogen Evolution Reaction

Hydrogen evolution reaction (HER) is one promising technique to obtain high-purity hydrogen, therefore, exploiting inexpensive and high-efficiency HER electrocatalysts is a matter of cardinal significance under the background of achieving carbon neutrality. In this paper, a hydrothermal method was used to prepare the Cr-NiC₂O₄/NF (Ni foam) precursor. Then, the NiO-Cr-C/NF self-supporting HER catalyst was obtained by heating the precursor at 400 °C. The catalyst presents a 3D cellular nanospheres structure which was composed of 2D nanosheets. Microstructure characterization shows that Cr and C elements were successfully doped into NiO. The results of electrochemical measurements and density functional theory (DFT) calculations show that under the synergy of Cr and C, the conductivity of NiO was improved, and the Gibbs free energy of H* (∆GH*) value is optimized. As a result, in 1.0 M KOH solution the NiO-Cr-C/NF-3 (Ni:Cr = 7:3) HER catalyst exhibits an overpotential of 69 mV and a Tafel slope of 45 mV/dec when the current density is 10 mA·cm^-2. Besides, after 20 h of chronopotentiometry, the catalytic activity is basically unchanged. It is demonstrated that C and Cr co-doping on the lattice of NiO prepared by a simple hydrothermal method and subsequent heat treatment to improve the catalytic activity and stability of the non-precious metal HER catalysts in an alkaline medium is facile and efficient.

A ternary PdNiMo alloy as a bifunctional nanocatalyst for the oxygen reduction reaction and hydrogen evolution reaction

Mo0.2Pd3Ni/NC shows superior electrochemical performances for both ORR and HER due to the charge redistribution among Ni, Pd, and Mo, tuning the electronic structure of Pd.