Hydrogen Evolution Reaction In Acidic Electrolyte Research Articles

Ionic liquid-assisted controlled synthesis of multi-site Ni2P as a bifunctional catalyst for electrocatalytic water splitting

It is crucial to develop effective electrocatalysts with multiple active sites for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in order to promote the advance energy conversion and development of sustainable energy technology. Here, we synthesized hierarchical nanostructured Ni2P on carbon cloth using ionic liquid (IL) assisted sacrificial template strategy through a simple two-step hydrothermal phosphatization process, which served as an electrode for enhancing bifunctional water electrolysis. By changing the content of ionic liquids in the solvent, the morphology of Ni(OH)2 precursors could be regulated, thereby altering the morphology of Ni2P. Ni2P exhibited remarkable electrocatalytic activity towards HER in acidic electrolytes with an overpotential of 132 mV at a current density of 10 mA cm−2, as well as OER in alkaline media with the overpotential of 309 mV. The excellent electrocatalytic activity of the Ni2P-2 could be attributed to its hierarchical nanostructure providing abundant active sites, which benefits from the structural end-capping effect of ILs.

MOF-derived ultrasmall Ru@RuO2 heterostructures as bifunctional and pH-universal electrocatalysts for 0.79 V asymmetric amphoteric overall water splitting

Developing heterostructures in nano-electrocatalyst has been demonstrated as a feasible method to enhance electrocatalytic activities for water splitting, since it still remains a grand challenge to develop highly efficient and stable electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) within a wide pH range. Herein, we report a facile pyrolysis strategy of Ru-MOF for rationally constructing ultrasmall Ru@RuO2 heterostructures, which exhibit extremely remarkable electrocatalytic performance toward both HER and OER in pH-universal electrolytes. Impressively, optimal Ru@RuO2-250 achieves ultralow overpotentials for both OER (198 mV, 263 mV and 182 mV @ 10 mA cm−2 in acidic, neutral and alkaline media) and HER (31 mV, 43 mV and 32 mV @ 10 mA cm−2 in acidic, neutral and alkaline media) due to the full exposure of highly active sites, which are derived from the synergism of abundant heterointerfaces, ultrafine heterostructure size and hierarchical porous structure with high surface area. Theoretical calculations reveal the charge rearrangement and electron conduction intensification near Ru-RuO2 heterointerfaces, the electronic structure changes of the active sites optimize the adsorption behavior toward various reaction intermediates, reducing the activation barriers and speeding up the reaction kinetics. Deservedly, an asymmetric-electrolyte electrolyzer employed with Ru@RuO2-250 is assembled to acquire an ultralow applied voltage of 0.79 V at 10 mA cm−2 based on amphoteric water electrolysis (HER in acidic electrolyte while OER in alkaline electrolyte).

Elucidating Catalytic Sites Governing the Performance toward the Hydrogen Evolution Reaction in Ternary Nitride Electrocatalysts

Proton exchange membrane electrolyzers are considered the most advanced devices for producing green hydrogen by water electrolysis. Their development requires catalytic materials that are stable under acidic conditions and drive the hydrogen evolution reaction (HER) forward efficiently which makes research into the identification of the catalytic sites important. We report that free-standing Co2Mo3N and Ni2Mo3N achieve overpotentials of 149 ± 8 and 158 ± 10 mV (in 0.5 M H2SO4) at a benchmark current density of 10 mA cm–2. Both nitrides remained stable and consistently deliver current densities >500 mA cm–2 at a potential as low as 308 ± 22 mV when they were immobilized on nickel foam. Replacing Ni for Fe in Ni2Mo3N leads to FexNi2–xMo3N (0.5 ≤ x ≤ 1.25) that show a decrease in catalytic activity as the value of x increases which confirms that Ni (rather than Mo and N) sites are catalytically active. The X-ray photoelectron spectroscopy data additionally suggests that preserving the low oxidation states of transition metals in the nitrides is important for achieving good catalytic performance toward the HER in acidic electrolytes.

Facile colloidal synthesis of transition metal (Co, Fe, and Ni)-added Ir-W NPs for HER in acidic electrolyte

Alloying earth-abundant transition metals with iridium, one of the promising catalysts for the hydrogen evolution reaction (HER), is an effective way to reduce the usage of precious metal without sacrificing its catalytic activity. In particular, tungsten and early transition metals (Co, Fe, and Ni) are known to promote the inherent HER activity by modulating surface adsorption energy, but ternary alloy nanoparticles (NPs) of those elements and their universal synthetic strategy are not well-established yet. In this study, we synthesized a new iridium-based ternary alloy NP with tungsten and transition metals of cobalt, iron, and nickel (Ir-M-W, M = Co, Fe, and Ni) through colloidal synthesis. All the constituent metal elements were uniformly distributed over the particle, forming a homogeneous solid solution. The Ir-M-W NPs showed excellent catalytic activity and mass activity toward HER in an acidic electrolyte compared with the binary Ir-W NPs. In particular, the Ir-Co-W NPs exhibited the lowest overpotential (35.82 mV of overpotential to drive −10 mA cm−2) and the highest mass activity (3.98 A/mgIr) with 40 µg cm−2 of catalyst loading. Such superior catalytic HER performance could be achieved by the modulation of the surface electronic structure induced by the inclusion of transition metal.

3D Carbon Electrode with Hierarchical Nanostructure Based on NiCoP Core‐Layered Double Hydroxide Shell for Supercapacitors and Hydrogen Evolution

AbstractCurrently, the development of self‐supported and low‐cost earth‐abundant electrocatalysts with well‐defined nanostructure has shown significant potential in energy‐related storage and electrocatalytic reactions. Herein, a three‐dimensional (3D) self‐supporting electrode NiCoP@NiCo LDH/CC (NCP@NCH/CC) constructed with NCP@NCH core‐shell nanostructures and carbon cloth as substrate has been developed via the hydrothermal and subsequent electrodeposition process. The obtained 3D electrode with 1D NiCoP nanowires (NWs) core and 2D NiCo LDH nanosheets shell can exhibit superior electrochemical performance and remarkable stability for the pseudocapacitive reaction and hydrogen evolution reaction (HER), even comparable to the best reported transition metal phosphides (TMP) electrodes. It reveals an ultra‐high area specific capacitance (9.4 F/cm2 at 10 mA/cm2 in 3 M KOH electrolyte), outstanding capacitance retention (74.12 % from 10 to 60 mA/cm2) and excellent cycling stability (93.51 % of original capacitance was retained after 5000 cycles at 50 mA/cm2) as supercapacitor electrode material. For HER in alkaline media, it can demonstrate an overpotential of 182 mV at 10 mA/cm2 and Tafel slope of 82 mV/dec in 1 M KOH. For HER in acidic electrolyte, it can exhibit an overpotential of 141 mV at 10 mA/cm2 and Tafel slope of 82 mV/dec in 0.5 M H2SO4. The electrochemical performance enhancement can be ascribed to the core‐shell NiCoP@NiCo LDH nanostructure anchored on the carbon and synergistic effect with the carbon cloth in 3D electrode. Our present work provides a facile strategy to construct 3D TMP‐based carbon electrode with core‐shell nanostructures, demonstrating a great promise for storage processes and energy conversion.

Uniform Formation of Amorphous Cobalt Phosphate on Carbon Nanotubes for Hydrogen Evolution Reaction†

Main observation and conclusionTremendous efforts have been made to the development of highly active, stable hydrogen evolution reaction (HER) electrocatalysts based on earth‐abundant metal compounds. Recently, cobalt phosphorus (Co‐P) catalysts have received particular attention owing to their good performances for the HER. However, the reported Co‐P catalysts were not uniformly anchored on the substrates. Hence, developing Co‐P catalysts with a uniform surface structure for HER remains a major challenge. Herein, we utilized small molecule tris(4‐fluorophenyl)phosphane (PF) for preliminarily functionalizing carbon nanotubes (PF‐CNTs) via π–π stacking interactions. Using these as the substrate, amorphous cobalt phosphate (CoPi) catalysts could then be uniformly anchored on PF‐CNTs by electrodeposition method. These obtained CoPi/PF‐CNTs catalysts show an onset potential low to 29 mV, a low overpotential (105 mV in 0.5 mol/L H2SO4 at a current density of 10 mA·cm–2 with a Tafel plot of 32 mV·dec–1) and an excellent stability for HER in acidic electrolyte, which is a promising noble‐metal‐free HER catalyst.

Fabrication of platinum thin films for ultra-high electrocatalytic hydrogen evolution reaction

While the noble metals (e.g., platinum, (Pt)) remain the benchmark electrocatalyst for the hydrogen evolution reaction (HER), their mass production require a reduced metal loading and faster fabrication protocols. The aim of the present work is to prepare Pt thin films by simple and fast fabrication technique, and to evaluate their performance for HER. The thin films of Pt are grown on two substrates, namely titanium foil (Ti) and nickel foam (NF), using a single step aerosol assisted chemical vapor deposition (AACVD) method. The film deposition time are varied from 20 to 60 min. Microscopic analyses suggest a gradual evolution of the films into percolated and/or porous nanostructures, a feature that remains highly desired to allow the maximum access of active sites. The performance of the as-prepared electrodes is evaluated by monitoring the HER in acidic electrolyte. The Pt film on nickel foam (Pt/NF) exhibits better electrical conductivity and smaller charge transfer resistance, while the film deposited on the Ti foil (Pt/Ti) demonstrates superior catalytic activity per active sites. The as-prepared Pt/Ti and Pt/NF electrodes produce 10 mA cm−2 at overpotential of 28 mV and 26 mV, respectively, better in performance than commercial Pt/C electrode (~39 mV), set a new bench mark electrocatalyst for the HER.

P-doped CNTs encapsulated nickel hybrids with flower-like structure as efficient catalysts for hydrogen evolution reaction

Electrochemical water splitting attracted an increasing attention as a promising approach to produce high-purity hydrogen. Both the design and synthesis of low-cost and high-performance catalysts for hydrogen evolution reaction (HER) remain challenging. Herein, an in-situ growth of carbon nanotubes encapsulated Ni particles on nickel foam is described. This catalyst is synthesized via a one-step chemical vapor deposition (CVD) at different temperatures followed by P-doping treatment (P-doped Ni@CNTs/NF). The corresponding physicochemical and electrochemical results illustrate that the P-doped Ni@CNTs/NF prepared at 600 °C with flower-like structure exhibits excellent activity and stability for HER in acidic electrolytes. In 0.5 M H2SO4 aqueous solution, the sample shows a small overpotential value of −135.2 mV to achieve a current density of −10 mA cm−2, which also displays acceptable long-term stability for lasting 20 h. This work provides a facile approach to prepare a cost-effective catalyst with high efficiency and might promote further study of the transition metal catalysts for hydrogen evolution in acid environments.

Stoichiometric Control of Electrocatalytic Amorphous Nickel Phosphide to Increase Hydrogen Evolution Reaction Activity and Stability in Acidic Medium

AbstractThis work describes the electrocatalysis of amorphous nickel phosphide (Ni‐P) electrodeposited onto copper metal foil, for its use as a non‐noble metal catalyst for the hydrogen evolution reaction (HER) in 0.5 M H2SO4. Although electrodeposition offers many advantages over conventional high temperature and high pressure fabrication techniques, there are very few reports on the preparation of Ni‐P electrocatalysts via electrodeposition. This Ni‐P electrocatalyst exhibits good activity in acidic medium, with a potential of –222 mV to achieve 10 mA cm–2 cathodic current density. This potential is comparable to that of electrodeposited Pt black (–104 mV), and much better than that of electrodeposited Ni (–480 mV). An unusual long‐term stability in acidic medium was demonstrated by the –222 mV potential remaining constant after 5000 cyclic voltammetric sweeps in 0.5 M H2SO4. Importantly, the stoichiometry of the nickel phosphide films can be easily varied from an atomic % of phosphorus from 15 % to as high as 24 % by modifications to the electrodeposition conditions. Such a high phosphorous loading is greater than is generally reported with electrodeposited Ni‐P materials. In addition, we observed Ni‐P films electrodeposited at lower temperatures (∼ 3 °C) result in higher phosphorous loading, which gives rise to enhanced stability as well as activity. Electrodeposited amorphous Ni‐P can therefore be used as an active, stable and Earth‐abundant metal catalyst for the HER in acidic electrolytes.

Molybdenum-Carbide-Modified Nitrogen-Doped Carbon Vesicle Encapsulating Nickel Nanoparticles: A Highly Efficient, Low-Cost Catalyst for Hydrogen Evolution Reaction.

Despite being promising substitutes for noble metal catalysts used in hydrogen evolution reaction (HER), the nonprecious metal catalysts (NPMCs) based on inexpensive and earth-abundant 3d transition metals (TMs) are still practically unfeasible due mainly to unsatisfactory activity and durability. Herein, a highly active and stable catalyst for HER has been developed on the basis of molybdenum-carbide-modified N-doped carbon vesicle encapsulating Ni nanoparticles (MoxC-Ni@NCV). This MoxC-Ni@NCV material was synthesized simply by the solid-state thermolysis of melamine-related composites of oxalate and molybdate with uniform Ni ions doping (Ni@MOM-com). Notably, the prepared MoxC-Ni@NCV was almost the most efficient NPMCs for HER in acidic electrolyte to date. Besides good long-term stability, MoxC-Ni@NCV exhibited a quiet low overpotential that was comparable to Pt/C. Thus, this work opens a new avenue toward the development of highly efficient, inexpensive HER catalysts.