Hydrogen Evolution Reaction Water Research Articles

Spontaneous hydrogen production on well-designed two-dimensional MoSi2N2P2 Janus structure: N-face versus P-face tuning

Based on the recently discovered two-dimensional non-Janus MoSi2N4 structure, we here study a well-designed two-dimensional Janus structure (MoSi2N2P2) for potential application in hydrogen evolution reaction (HER) via water splitting. We first confirm the stability of the MoSi2N2P2 structure using first-principles’ calculations in the framework of density functional theory by calculating cohesive energy, phonon dispersion, and ab-initio molecular dynamics evolution. We then investigate electronic and transport properties of the structure. The MoSi2N2P2 Janus structure exhibits an indirect (Γ→M) band gap of only 0.22 eV using PBE and 0.89 eV using the HSE06 hybrid functional. We also find that there is a large intrinsic electric field across the Janus structure, which tends to gather electrons at the P face. We also calculate the mobility of the Janus structure, showing that it has a high electron mobility (409 cm2/Vs) along the zigzag direction. We then show that compared with the P face, the N face gives a lower overpotential against HER, but not sufficient to activate HER process. Therefore, we investigate how the electronic properties and the HER overpotential of the Janus MoSi2N2P2 monolayer are affected by applying biaxial strain and external perpendicular electric field. Thus, the N face exhibits a higher degree of tunability than the P face toward HER overpotential. In particular by applying an electric field of 2.7 V/Å directing from the P face to the N face, the overpotential against the HER reaction on the N face can be adjusted to zero, showing that the well-designed Janus structure can exhibit a potential application for spontaneous HER water splitting.

High phase purity of stable 1T-phase Co-doped WS2 for full pH hydrogen evolution reaction in water and seawater

Metallic 1T phase transition metal dichloride (TMDs) shows excellent catalytic activity for the hydrogen evolution reaction (HER), but stabilization of 1T phase TMDs is still challenging. Herein, the Finke-type POMs K10[Co4(H2O)2(PW9O34)2] [Co4(PW9)2] was used for the first time as a precursor to obtaining size ∼ 4 nm, highly dispersed 1T-WS2 in the hollow mesoporous carbon sphere (HMCS) by the effect of confinement, named 1T-CoWS/HMCS. 1T-WS2 was obtained based on the natural Co-W atomic interface of POMs and further enhanced dispersion at the molecular and nano scales. 1T-CoWS/HMCS only requires ultralow overpotential with high electrocatalytic surface area and robust stability in water and seawater. According to DFT calculations, the Co-S-edge site of 1T-CoWS significantly reduced the rate-limiting step of HER as the predominant active site. This work provides a worthy reference for the synthesis of high-quality metastable TMDs.

Diiodo-BODIPY Sensitizing of the [Mo3S13]2- Cluster for Noble-Metal-Free Visible-Light-Driven Hydrogen Evolution within a Polyampholytic Matrix.

We report on a photocatalytic setup that utilizes the organic photosensitizer (PS) diiodo-BODIPY and the non-precious-metal-based hydrogen evolution reaction (HER) catalyst (NH4)2[Mo3S13] together with a polyampholytic unimolecular matrix poly(dehydroalanine)-graft-poly(ethylene glycol) (PDha-g-PEG) in aqueous media. The system shows exceptionally high performance with turnover numbers (TON > 7300) and turnover frequencies (TOF > 450 h-1) that are typical for noble-metal-containing systems. Excited-state absorption spectra reveal the formation of a long-lived triplet state of the PS in both aqueous and organic media. The system is a blueprint for developing noble-metal-free HER in water. Component optimization, e.g., by modification of the meso substituent of the PS and the composition of the HER catalyst, is further possible.

Early Transition-Metal-Based Binary Oxide/Nitride for Efficient Electrocatalytic Hydrogen Evolution from Saline Water in Different pH Environments.

Using abundant seawater can reduce reliance on freshwater resources for hydrogen production from electrocatalytic water splitting. However, seawater has detrimental effects on the stability and activity of the hydrogen evolution reaction (HER) electrocatalysts under different pH conditions. In this work, we report the synthesis of binary metallic core-sheath nitride@oxynitride electrocatalysts [Ni(ETM)]δ+-[O-N]δ-, where ETM is an early transition metal V or Cr. Using NiVN on a nickel foam (NF) substrate, we demonstrate an HER overpotential as low as 32 mV at -10 mA cm-2 in saline water (0.6 M NaCl). The results represent an advancement in saline water HER performance of earth-abundant electrocatalysts, especially under near-neutral pH range (i.e., pH 6-8). Doping ETMs in nickel oxynitrides accelerates the typically rate-determining H2O dissociation step for HER and suppresses chloride deactivation of the catalyst in neutral-pH saline water. Heterointerface synergism occurs through H2O adsorption and dissociation at interfacial oxide character, while adsorbed H* proceeds via Heyrovsky or Tafel step on the nitride character. This electrocatalyst showed stable performance under a constant current density of -50 mA cm-2 for 50 h followed by additional 50 h at -100 mA cm-2 in a neutral saline electrolyte (1 M PB + 0.6 M NaCl). Contrarily, under the same conditions, Pt/C@NF exhibited significantly low performance after a mere 4 h at -50 mA cm-2. The low Tafel slope of 25 mV dec-1 indicated that the reaction is Tafel limited, unlike commercial Pt/C, which is Heyrovsky limited. We close by discussing general principles concerning surface charge delocalization for the design of HER electrocatalysts in pH saline environments.

Cu2O/CuO heterojunction catalysts through atmospheric pressure plasma induced defect passivation

A novel route to fabricate Cu2O/CuO heterojunction electrodes using an atmospheric pressure plasma jet (APPJ) is demonstrated. This process promotes favourable band alignment and produces nanoscale CuO surface features from Cu2O with low density of interfacial defects. This electrode can operate without any transparent current collector, showing remarkable currents and stability towards oxygen evolution reaction (OER) (6 mA cm−2 for 2 h at pH14) as well as photocatalytic hydrogen evolution reaction (HER) activity (−1.9 mA cm−2 for 800 s at pH7). When the electrocatalytic oxygen evolution (OER) activity was measured for Cu2O/CuO electrode deposited on FTO substrate the currents increased to ~40 mA cm−2 at 0.8 V vs SCE in 1 M KOH without compensating for the electrode electrolyte surface resistance (iR correction). The composite films also exhibited a high rate towards photo degradation of Methylene Blue (MB) and phenol in the visible spectra, indicating efficient charge separation. We modelled the electronic structure of this epitaxially grown Cu2O/CuO heterojunction using density functional theory. The calculations revealed the distinctive shifts towards Fermi level of the p-band centre of O atom in Cu2O and d-band centre of Cu atom in CuO at the interface contribute towards the increased catalytic activity of the heterostructure. Another factor influencing the activity stems from the high density of excited species in the plasma introducing polar radicals at the electrode surface increasing the electrolyte coverage. This work presents the potential of APPJ functionalization to tune the surface electronic properties of copper oxide based catalysts for enhanced efficiency in OER and HER water splitting.

Defect-rich exfoliated MoSe2 nanosheets by supercritical fluid process as an attractive catalyst for hydrogen evolution in water

Single- to few-layers MoSe2 nanosheets were obtained from bulk MoSe2 by a supercritical fluid exfoliation. High angle annular dark field (HAADF) imaging showed the presence of a great variety of vacancies and edge defects within the exfoliated MoSe2 nanosheets. Thanks to these defects, the exfoliated MoSe2 nanosheets showed attractive catalytic performance and robustness for the hydrogen evolution reaction in water. The best electrode made of these nanosheets required 300 mV overpotential to generate a catalytic current of 10 mA/cm2 and showed a Tafel slop of 90 mV/s. The catalytic performance was further enhanced by twice when the MoSe2 nanosheets catalyst was conditioned at a mild oxidative potential, e.g.+0.73 V vs. RHE. The mild oxidation treatment was proposed to create novel Se-vacancy and Se2-vacancy while an oxidation treatment at higher potential, e.g. +1.23 V vs. RHE, completely oxidized MoSe2 into inactive MoO3. As a consequence, the later caused a rapid degradation of catalytic performance.

Insights into the Electrochemical Polymerization of [Mo3 S13 ]2- Generating Amorphous Molybdenum Sulfide.

Amorphous molybdenum sulfide is an attractive electrode material for Li/Mg batteries and an efficient Pt-free catalyst for the hydrogen evolution reaction in water. By using the electrochemical quartz crystal microbalance (EQCM) analysis, new insights were gained into the electrochemical polymerization of the [Mo3 S13 ]2- cluster, which generates amorphous molybdenum sulfide thin films. In this work, it is shown that, at the anodic potential, a two-electron oxidative elimination of the terminal disulfide ligand within the [Mo3 S13 ]2- cluster induces the polymerization. A reductive elimination of the terminal disulfide ligand also occurs at the cathodic potential, inducing the polymerization. However, in sharp contrast to the anodic polymerization, according to which the film growth is rapid, the cathodic polymerization competes with the electrochemical reductive corrosion of the readily grown film, therefore occurring at a significant lower growth rate.

Interfacial Sites between Cobalt Nitride and Cobalt Act as Bifunctional Catalysts for Hydrogen Electrochemistry

Hydrogen (H2) electrochemistry primarily consists of two reactions: hydrogen evolution reaction in water for H2 production (HER) and hydrogen oxidation reaction in hydrogen fuel cells for H2 utiliz...

Crystal Phase Dependence on HER Water Splitting Performance of Earth-Abundant Electrocatalysts

Economical hydrogen production via renewable-energy-powered water splitting is only feasible with earth-abundant low over-potential (<150 mV @ 10 mA/cm2) electrocatalysts. Nickel-molybdenum alloys, as earth-abundant electrocatalysts, have been reported to show competitive performance characteristics over past years. Herein, we will present stoichiometric ratios that result in multiple crystal phases and alkaline hydrogen evolution reaction (HER) over-potentials. In particular, the performance of specific transition metal crystal phases in alkaline media were evaluated for HER performance with general knowledge of that alkaline media leads to higher stabilities over acidic media. Typically, alkaline media also limits low over-potentials. In our case, specific phases of NixMo showed competitive over-potentials regardless of electrolyte. Colloidal nanocrystals were synthesized and drop-casted onto titanium foil to form fashioned single crystal phase electrodes. Electrodepositing, contrary to drop-casting, films might result in good electrode stability and performance but cannot easily provide experimental elucidation of crystal phase dependence on HER over-potential. A more robust method is needed to differentiate long-term stability differences for fashioned electrodes in 2M KOH. Structural crystal phase differences between different colloidal nanocrystal alloy compositions will be presented as x-ray photoelectron spectroscopy (XPS) and x-ray powder diffraction (XRD) data. Electrochemical data, including polarization curves and Tafel plots, will be presented. Specific insights into over-potential differences of alloys with similar elemental composition was gained and a discussion linking metal oxidation states to over-potential performance will take place.

Novel Amorphous Molybdenum Selenide as an Efficient Catalyst for Hydrogen Evolution Reaction.

Amorphous molybdenum selenide nanopowder, obtained by refluxing Mo(CO)6 and Se precursors in dichlorobenzene, shows several structural and electrochemical similarities to the amorphous molybdenum sulfide analogue. The molybdenum selenide displays attractive catalytic properties for the hydrogen evolution reaction in water over a wide range of pH. In a pH 0 solution, it operates with a small onset overpotential of 125 mV and requires an overpotential of 270 mV for generating a catalytic current of 10 mA/cm2. Compared with molybdenum sulfide, the selenide analogue is more robust in a basic electrolyte. Therefore, molybdenum selenide is a potential candidate for incorporating within an electrolyzer or a photoelectrochemical cell for water electrolysis in acidic, neutral, or alkaline medium.

Gold nanoparticles as an outstanding catalyst for the hydrogen evolution reaction.

An electrode made of Au nanoparticles, ca. 13 nm in diameter, displays outstanding catalytic activity for the hydrogen evolution reaction in water. At an overpotential of 200 mV it operates with a catalytic rate TOF of 0.3 s-1, which is among the best performances ever achieved for a Pt-free H2-evolving catalyst.

In-situ activation of self-supported 3D hierarchically porous Ni3S2 films grown on nanoporous copper as excellent pH-universal electrocatalysts for hydrogen evolution reaction

The exploitation of low-cost, stable, and highly active electrocatalysts based on earth-abundant metals for hydrogen evolution reaction (HER) is crucial for developing renewable energy techniques. In this work, we report a facile synthesis strategy for in-situ fabrication of 3D hierarchically porous Ni3S2 films on a nanoporous copper substrate (Ni3S2@NPC) by unusual galvanic replacement reaction in the Ethaline-based deep eutectic solvent (DES) under a normal atmosphere. The self-supported nanoporous Ni3S2@NPC electrode is binder- free and exhibits good structural integrity with high conductivity. A mild evolution of bulk gas bubbles (H2-O2 gas mixture) is proved to drive an in-situ structure rearrangement process of the Ni3S2@NPC and results in substantial increases in the HER activity. The activated Ni3S2@NPC (a-Ni3S2@NPC) electrode can serve as a highly efficient and stable electrocatalyst for the HER in water over a wide pH range. Significantly, it displays high-performance HER catalytic activity in acidic media with robust durability over 111h and functions well under alkaline and neutral conditions. Such a superior catalytic performance of the a-Ni3S2@NPC is mainly due to the unique hierarchically nanoporous architectures and the synergetic effects in it caused by the restructuring NPC skeletons and active components. Our work offers a generic strategy for design and fabrication of many other self-supported transition metal sulfide and phosphide based HER electrocatalysts, and uncovers a new O2-induced electrochemical self-activation mechanism for improving the activity of catalysts.

Electrodeposition of Cu–In alloys from a choline chloride based deep eutectic solvent for photovoltaic applications

Electrodeposition and post-annealing is a promising low-cost approach to the growth of Cu(In,Ga)Se2 for photovoltaic applications. However, In and Ga electrodeposition is not facile from aqueous electrolytes. Efficient electrodeposition can be achieved by using deep eutectic solvent (DES) based electrolytes since solvent decomposition reactions (such as hydrogen evolution reaction in water) do not occur.In this work, the electrochemical behavior of InCl3 and CuCl2–InCl3 on the DES 1:2 choline chloride:urea (ChCl:U) on a Mo rotating disk electrode is studied via cyclic voltammetry. The deposited Cu–In thin films are characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) in terms of morphology and composition and X-ray diffraction (XRD) regarding crystal structure. The cyclic voltammetric studies on the ChCl:U–CuCl2–InCl3 system showed multiple cathodic and anodic responses, which were assigned to various crystalline phases. The crystalline phases, composition and morphology of the deposits were potential dependent. Cu–In intermetallics formation is studied as a function of deposition potential and electrolyte composition. Cu–In metal precursors were thermally annealed under selenium pressure to form CuInSe2.

Novel cobalt/nickel–tungsten-sulfide catalysts for electrocatalytic hydrogen generation from water

The potential of water (photo)electrolysis technology to provide hydrogen as a fuel on a large scale depends on how viable electrocatalysts for the water oxidation reaction (WOR) and the hydrogen evolution reaction (HER) are and whether they can be constructed from elements which are abundant in the Earth's crust. Here we show that ternary sulfides of cobalt–tungsten and nickel–tungsten (MWSx where M is Co or Ni) are efficient and robust electrocatalysts for the HER in water over a wide pH range. These novel ternary sulfides were readily grown on a conducting electrode surface by employing a scalable electrodeposition process from aqueous solutions of [M(WS4)2]2−. In terms of HER activity, the MWSx catalysts represent attractive alternatives to platinum. Moreover, we show that the HER activity is governed by the nature of the metal M within M–S–W heterobimetallic sulfide centres, located in the WS2-like layered structure of MWSx. Our work provides structural and mechanistic keys to understand how HER activity is promoted in previously described nickel and cobalt-doped molybdenum and tungsten sulfide materials.