A novel MoNi@Ni(OH)2 heterostructure with Pt-like and stable electrocatalytic activity for the hydrogen evolution reaction

Interfacial engineering of POM-stabilized Ni quantum dots on porous titanium mesh for high-rate and stable alkaline hydrogen production

The development of low-cost, high-efficiency, and stable electrocatalysts for the alkaline hydrogen evolution reaction (HER) is a key challenge because the alkaline HER kinetics is slowed by an additional water dissociation step. Herein, we report an interfacial engineering strategy for polyoxometalate (POM)-stabilized nickel (Ni) quantum dots decorated on the surface of porous titanium mesh (POMs-Ni@PTM) for high-rate and stable alkaline hydrogen production. Benefiting from the strong interfacial interactions among POMs, Ni atoms, and PTM substrates, as well as unique POM-Ni quantum dot structures, the optimized POMs-Ni@PTM electrocatalyst exhibits a remarkable alkaline HER performance with an overpotential (η10) of 30.1 mV to reach a current density of 10 mA cm-2, which is much better than those of bare Ni decorated porous titanium mesh (Ni@PTM) (η10 = 171.1 mV) and POM decorated porous titanium mesh (POMs@PTM) electrocatalysts (η10 = 493.6 mV), comparable to that of the commercial 20 wt% platinum/carbon (20% Pt/C) electrocatalyst (η10 = 20 mV). Moreover, the optimized POMs-Ni@PTM electrocatalyst demonstrates excellent stability under continuous alkaline water-splitting at a current density of ∼100 mA cm-2 for 100 h, demonstrating great potential for its practical application.

Pt nanoparticle dispersed Ni(OH)2 nanosheets via a pulsed laser deposition method efficiently enhanced hydrogen evolution reaction performance in alkaline conditions

The use of electrochemical water is a very attractive and environmentally friendly solution for hydrogen fuel production. Platinum (Pt) catalysts are considered to be the most active catalyst for the hydrogen evolution reaction (HER) but suffer from low efficiency and slow kinetics. Herein, Pt nanoparticles dispersed Ni(OH)₂ nanosheets (Pt-Ni(OH)₂-X) with different deposition times were designed and developed via a vapour-phase hydrothermal method, followed by a pulsed laser deposition method. The Pt-Ni(OH)₂-5 only needs overpotentials of 247.5 ± 43 and 512.5 ± 18 mV to reach current densities of 10 and 100 mA cm^-2, respectively, outperforming the commercial Pt/C at a current density of 100 mA cm^-2. Furthermore, the infrared spectrum revealed that the adsorption of water molecules becomes stronger at the surface of the Pt-Ni(OH)₂-5 nanosheets, and the hydrogen protons overflow onto the Pt surface and facilitate the HER process. This work suggests that moderate Pt nanoparticle dispersed Ni(OH)₂ nanosheet help to promote the hydrogen production process.

Transition metal oxy/hydroxides functionalized flexible halloysite nanotubes for hydrogen evolution reaction

The hierarchical halloysite nanotubes (HNT) have alumina containing positive Al-OH groups on its inner surface and silica-containing negative siloxane groups of Si-O-Si on its outer surface. The silicate laminate consists of silicon-oxygen at tetrahedral sites and aluminum-oxygen at octahedral sites. Since HNT has an abundant hydroxyl group on the surface with exceptional cation/anion exchange capacity, the surface-functionalized HNT could boost electrocatalytic activity. Hence, we have synthesized Ni, Co, and Cu metal oxy/hydroxides functionalized HNT by a facile hydrothermal method for HER. Among them, Co(OH)₂@HNT on flexible carbon cloth displays an ultra-low overpotential of 65 mV at 10 mA cm^-2 current density and Tafel slope of 181 mV dec^-1 and also exhibited a larger exchange current density of 3.98 mA cm^-2 in alkaline 1 M KOH electrolyte due to superior electrostatic affinity between OH^- and Co²⁺. The electrolyzers with anion exchange membrane consisting of RuO₂||Co(OH)₂@HNT show remarkable stability of over 50 h at 10 mA cm^-2 in alkaline electrolyte. The post stability sample retains the same surface oxidation state which confirms the robustness of the electrocatalyst. The reported results are far better than many of the transition metal oxides/chalcogenides electrocatalysts and hence it is expected that HNT could act as a potential alternative candidate to replace the benchmark platinum catalyst.

(Ni,Co)Se@Ni(OH)2 heterojunction nanosheets as an efficient electrocatalyst for the hydrogen evolution reaction

A heterogeneous structure formed by coupling two or more phases can reinforce the activity of active sites and expedite electron transfer, which is conducive to boosting its electrocatalytic activity. Herein, we designed nickel foam supported (NiCo₂)Se@Ni(OH)₂ (NCS@NH) heterojunction nanosheets by a two-step method. First of all, the NiCo₂S₄@Ni(OH)₂ (NiCo₂S₄@NH) nanosheets coated on nickel foam were acquired via a hydrothermal method. In the selenization treatment that followed, NiCo₂S₄@NH was converted into NCS@NH heterogeneous nanosheets in which the selenide nanoparticles decorated on the surface of the Ni(OH)₂ nanosheets formed heterojunction interfaces, and the heterogeneous structure could accelerate electron transfer, thus improving the catalytic activity. The Ni(OH)₂ nanosheets can adequately contact the electrolyte and promote the decomposition of water. Meanwhile, the thickness of the Ni(OH)₂ nanosheets gradually decreases with the increase of Co doping (1.5-2.5 mmol), consequently affecting the HER properties. Notably, when the amount of Co salt added is 2 mmol, NCS@NH exhibited superior HER properties (with a voltage of 253 mV at 100 mA cm^-2) and excellent stability for 24 h.

Enhanced Electron Transfer and Ion Transport by Binary and Multidimensional CuCo2 S4 /Fe2 O3 on Carbon Cloth for Water Oxidation

The behavior of electron transfer and ion transport plays a significant role in the electrocatalytic activity. However, the improvement of CuCo₂ S₄ electrocatalytic activity has been a difficult problem owing to lack of effective electron transfer and ion transport. Herein, the unique structure connected CuCo₂ S₄ nanosheets and carbon cloth (CC) with Fe₂ O₃ nanoparticles to form CuCo₂ S₄ /Fe₂ O₃ /CC. Compared with CuCo₂ S₄ /CC, the resistances of electron transfer and ion transport were decreased by 65 and 84 %, respectively. The electrochemical surface area of CuCo₂ S₄ /Fe₂ O₃ /CC was 2.76 times larger than that of CuCo₂ S₄ /CC due to the high double-layer capacitance. For the oxygen evolution reaction, CuCo₂ S₄ /Fe₂ O₃ /CC could achieve an overpotential of 273 mV and a Tafel slope of 67 mV dec^-1 in alkaline solution.

Regulating the electronic structure of CoMoO4 microrod by phosphorus doping: an efficient electrocatalyst for the hydrogen evolution reaction

It is of extreme importance to design efficient electrocatalysts for hydrogen evolution reaction (HER), which is considered as a promising approach to provide efficient and renewable clean fuel (hydrogen). Tuning the electronic structure through heteroatom doping demonstrates one of the most effective strategies to promote the electrocatalytic performance of HER. Herein, phosphorus-doping modulation is utilized to fabricate monoclinic P-CoMoO₄ with optimized electron structure supported on nickel foam (P-CoMoO₄/NF) for alkaline HER via a facile hydrothermal method, followed by low-temperature phosphidation. Notably, P-CoMoO₄/NF shows outstanding electrocatalytic performance for HER in 1 M KOH with a low overpotential of 89 mV at 10 mA cm^-2, a remarkable Tafel slope value of 59 mV dec^-1, and excellent 24 h-long stability. The excellent catalyst activity and stability merits of P-CoMoO₄/NF are comparable to the reported highly efficient non-precious metal HER electrocatalysts and could be applied as a powerful electrocatalyst in water electrolysis. This work provides a superior synthesis strategy for the effective design and rational fabrication of low-cost, highly active, and highly stable non-precious metal HER electrocatalysts for electricity-to-hydrogen applications.