Electrode For Hydrogen Evolution Reaction Research Articles

Construction of NiCo2S4/Ni3S2 nanoarrays on Ni foam substrate as an enhanced electrode for hydrogen evolution reaction and supercapacitors

Developing a multifunctional and sustainable electrode material for hydrogen evolution reaction and supercapacitors is a highly feasible avenue for producing the high energy density and renewable energies. In our study, nanostructured NiCo2S4/Ni3S2/NF nanoarrays are rational developed in experiments via a simple hydrothermal reaction. Ascribed to the 3D nanostructured NiCo2S4/Ni3S2 with numerous exposure active sites and large contact areas for the electrolyte, the binder-free feature of NiCo2S4/Ni3S2/NF facilitates a low charge transfer resistance, as well as the synergetic effect of NiCo2S4 and Ni3S2. The obtained electrocatalyst showed ultrahigh electrocatalytic activity with an overpotential of 111 mV at 10 mA cm−2 and a Tafel slope of 57 mV dec−1. In addition, the electrode showed an area specific capacity of 6.13 F cm−2 at 10 mA cm−2 and superior rate capability (2.72 F cm−2 at 80 mA cm−2), accompanied by excellent cycling stability. This results presented in our work can provide an effective strategy for rational design of other hybrid materials with excellent electrochemical performance in the application of electrocatalysis and supercapacitors.

Revealing the effect of electrocatalytic performance boost during hydrogen evolution reaction on free-standing SWCNT film electrode

Large-scale sustainable hydrogen production by water electrolysis requires a highly active yet low-cost hydrogen evolution reaction (HER) electrocatalyst. Conductive carbon nanomaterials with high surface areas are promising candidates for this purpose. In this contribution, single-walled carbon nanotubes (SWCNTs) are assembled into free-standing films and directly used as HER electrodes. During the initial 20 h of electrocatalytic performance in galvanostatic conditions, the films undergo activation, which results in a gradual overpotential decrease to the value of 225 mV. Transient physicochemical properties of the films at various activation stages are characterized to reveal the material features responsible for the activity boost. Results indicate that partial oxidation of iron nanoparticles encapsulated in SWCNTs is the major contributor to the activity enhancement. Furthermore, besides high activity, the material, composed of only earth-abundant elements, possesses exceptional performance stability, with no activity loss for 200 h of galvanostatic performance at − 10 mA cm−2. In conclusion, the work presents the strategy of engineering a highly active HER electrode composed of widely available elements and provides new insights into the origins of electrocatalytic performance of SWCNT-based materials in alkaline HER.

Characterizing the Onset Potential Distribution of Pt/C Catalyst Deposition by a Total Internal Reflection Imaging Method.

A catalytic electrode with extraordinary performances for hydrogen evolution reaction (HER) should achieve a low onset potential of the bulk electrode, as well as its uniform distribution. Herein, a total internal reflection imaging (TIRi) method to characterize the onset potential distribution of the catalytic electrode surface is presented. When the potential scans toward negative in a linear sweep voltammetry, the equivalent refractive index of the electrolyte on the electrode surface will decrease due to H2 microbubbles generation, leading to the increase in optical intensity. Analysis of the relationship between the optical intensity and potential in each region results in the onset potential distribution. The TIRi method reveals poor uniformity and repeatability in the catalytic electrodes which are fabricated by depositing Pt/C catalysts on a porous carbon support with polymer binders (e.g.,Nafion). Further electrochemical stability test also shows poor durability, whose HER onset potential deteriorates from the edge to the middle of these catalytic electrodes. The present TIRi method realizes direct visualization of the activity distribution on the bulk electrode surface, which provides a powerful tool for better fabrication and evaluation of large-area HER electrodes in industrial energy devices.

Design of Aligned Porous Carbon Films with Single-Atom Co-N-C Sites for High-Current-Density Hydrogen Generation.

Metal- and nitrogen-doped carbon (M-N-C) materials as a unique class of single-atom catalysts (SACs) have increasingly attracted attention as the replacement of platinum for the hydrogen evolution reaction (HER); however, their employment as HER electrodes at high current densities of industrial level remains a grand challenge. Herein, an aligned porous carbon film embedded with single-atom Co-N-C sites of exceptional activity and stability at high current densities is designed. Within the film, the atomic CoNx moieties exhibit high intrinsic activity, while the multiscale porosity of the carbon frameworks with vertically aligned microchannels afford facilitated mass transfer under the conditions of high production rate and ultrathick electrodes. Moreover, the superwetting properties of the film promote electrolyte wetting and ensure the timely removal of the evolving H2 gas bubbles. The as-designed film can work as an efficient HER electrode to deliver 500 and 1000mA cm-2 in acid at overpotentials of 272 and 343mV, respectively, and can operate uninterruptedly and stably at 1000mA cm-2 for at least 32 h under static conditions. These findings pave the road toward the rational design of SACs with improved activity and stability at high current densities in gas-evolving electrocatalytic processes.

NaBH4-electrooxidation mediated electrodeposition of catalytic Pt nanoparticles on a honeycomb-gold electrode for hydrogen evolution reaction

We report the NaBH4-electrooxidation mediated electrodeposition of platinum nanoparticles (PtNPs) on a pulse-plated gold (Aupla) and three-dimensional honeycomb-like porous nano-golds (3DHPNG) modified glassy carbon electrode (GCE), for electrocatalytic hydrogen evolution reaction (HER). The 3DHPNG of large surface area was deposited on Aupla/GCE at −4.76 V versus RHE for 200 s in 5 M aqueous H2SO4 containing 15 mM HAuCl4, by dynamic hydrogen bubble template. The uniform electrodeposition of PtNPs on 3DHPNG/Aupla/GCE at 1.24 V versus RHE was achieved in 25 mM aqueous NaClO4 containing 5.37 μM PtNPs dispersion that was obtained by mixing aqueous NaBH4, trisodium citrate and H2PtCl6. The electrodeposition mechanism is explained by the electrogeneration of H+ through the electrooxidation of residual NaBH4 and its oxidation intermediates, which can neutralize the negative surface-charges of some PtNPs and make the PtNPs coagulate on the electrode surface, and some new insights into the oxidation of so widely used NaBH4 on the anode and by H2PtCl6 and water are also provided. The optimized PtNPs/3DHPNG/Aupla/GCE exhibited good electrocatalytic performance for HER in 0.5 M aqueous H2SO4, giving an overpotential of 10.0 mV at −10 mA cm−2 and a Tafel slope of 25.2 mV dec−1, being better than those of many reported electrodes.

Facile Fabrication of Robust Hydrogen Evolution Electrodes under High Current Densities via Pt@Cu Interactions

AbstractDurable and efficient hydrogen evolution reaction (HER) electrocatalysts that can satisfy industrial requirements need to be developed. Platinum (Pt)‐based catalysts represent the benchmark performance but are less studied for HER under high current densities in neutral electrolytes due to their high cost, poor stability, and extra water dissociation step. Here a facile and low‐temperature synthesis for constructing “blackberry‐shaped” Pt nanocrystals on copper (Cu) foams with low loading as self‐standing electrodes for HER in neutral media is proposed. Optimized hydrogen adsorption free energy and robust interaction induced by charge density exchange between Pt and Cu ensure the efficient and robust HER, especially under high current densities, which are demonstrated from both experimental and theoretical approaches. The electrode exhibits small overpotentials of 35 and 438 mV to reach current densities of ‐10 and ‐1000 mA cm−2, respectively. Meanwhile the electrode illustrates outstanding stability during chronoamperometry measurement under high current densities (‐100 to ‐400 mA cm−2) and 1000 cycles linear sweep voltammetry tests reaching ‐1000 mA cm−2. This study provides new design strategies for self‐standing electrocatalysts by fabricating robust metal–metal interactions between active materials and current collectors, thus facilitating the stable function of electrodes for HER under technologically relevant high current densities.

Layer‐by‐Layer Assembly‐Based Electrocatalytic Fibril Electrodes Enabling Extremely Low Overpotentials and Stable Operation at 1 A cm−2 in Water‐Splitting Reaction

AbstractFor the practical use of water electrolyzers using non‐noble metal catalysts, it is crucial to minimize the overpotentials for the hydrogen and oxygen evolution reactions. Here, cotton‐based, highly porous electrocatalytic electrodes are introduced with extremely low overpotentials and fast reaction kinetics using metal nanoparticle assembly‐driven electroplating. Hydrophobic metal nanoparticles are layer‐by‐layer assembled with small‐molecule linkers onto cotton fibrils to form the conductive seeds for effective electroplating of non‐noble metal electrocatalysts. This approach converts insulating cottons to highly electrocatalytic textiles while maintaining their intrinsic 3D porous structure with extremely large surface area without metal agglomerations. To prepare hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrodes, Ni is first electroplated onto the conductive cotton textile (HER electrode), and NiFe is subsequently electroplated onto the Ni–electroplated textile (OER electrode). The resulting HER and OER electrodes exhibit remarkably low overpotentials of 12 mV at 10 mA cm−2 and 214 mV at 50 mA cm−2, respectively. The two‐electrode water electrolyzer exhibits a current density of 10 mA cm−2 at a low cell voltage of 1.39 V. Additionally, the operational stability of the device is well maintained even at an extremely high current density of 1 A cm−2 for at least 100 h.

Correlation of Exchange Current Density j₀ and the Standard Potential of the Metal Electrodes E0 M : A Different View of the Hydrogen Evolution Reaction (HER)

Technologically, the hydrogen evolution reaction (HER) is the foundation of many electrochemical energy systems. Fundamentally, HER is important as 2H+ + 2e ⇌ H2 defines the standard reference potential E0 H = 0.000 V in thermodynamics. All evolutions in kinetic theory are critically tested against HER.In electrocatalysis, the HER mechanism is historically specified in three steps. The first step, Volmer, couples concerted adsorption and reduction of proton to form electrochemically adsorbed hydrogen.H+ + e ⇄ Hads (Volmer) (1)Once the first proton electroadsorbs, H2 forms by two parallel pathways. The Heyrovsky step proceeds as a second proton is electroadsorbed to the same metal atom and hydrogen gas desorbs from the common metal center.Hads + H+ + e ⇄ H2 (Heyrovsky) (2)In the Tafel step, electrochemically adsorbed hydrogen forms on an adjacent metal center and H2 desorbs.Hads + Hads ⇄ H2 (Tafel) (3)Commonly, HER electrode kinetics are evaluated according to the Volmer-Heyrovsky-Tafel scheme, where rate is measured as exchange current densities j₀. For HER at metal electrodes, log j₀ depends strongly on the electrode metal where log j₀ falls between -3 for Pt, Re, and Pd and -12 for Hg. Although metals are not explicit in the Volmer-Heyrovsky-Tafel scheme, j₀ is evaluated in view of Steps (1) to (3). Here, metal electrode properties are introduced as the standard potential E0 M of the electrode metal. For metal cation reduction to metal M⁰,Mz+ + ze ⇌ M⁰ E0 M log j₀ values are cataloged in a paper by Trasatti (Electroanalytical Chemistry and Interfacial Electrochemistry 1972, 39, 163-184), where he partitioned 31 metal electrodes into d and sp metals. For the transition metals, the d metals, log j₀ is well and linearly correlated with E0 M . For the sp metals, there is little to no correlation of log j₀ with E0 M .For the transition metals, several observations and a model sketch are noted. HER rates as log j₀ increase with more positive values of E0 M .For the initial step of the metal dependent HER process, it is sketched that electron(s) release from M0 to form Mz+ immediately at the electrode surface.For this initial step, formation of Mz+ immediately at the electrode solution interface yields log j₀ linearly dependent on E0 M .Within transition state or activated complex theory, a proposed transition state is formed of electron(s) shared between Mz+ and H+.Formation of the transition state [(1/z)Mz+⋯e⋯H+]‡ precedes the Volmer step, and where applicable, is a rate determining step.Overpotential η pinned by E0 M may characterize the counter intuitive observation that rate (log j₀) increases as E0 M is more positive.This sketch of HER yields a kinetic model where a component of the activation energy is set by F(E0 H -E0 M ). The sketch of an electrode dependent transition state may pose a general approach to characterizing electrocatalysis and interfacial electron transfers. The proposed transition state introduces physical properties of specific electrode materials into the rate expressions a priori.

Ni–P alloy@carbon nanotubes immobilized on the framework of Ni foam as a 3D hierarchical porous self-supporting electrode for hydrogen evolution reaction

The development of self-supporting electrodes that exhibited both high efficiency and good durability remained a challenge in the field of hydrogen energy utilisation. Here, we designed a self-supporting 3D hierarchical porous electrode by filling carbon nanotubes (CNTs) loaded with Ni–P alloy into the framework of nickel foam (NF). Firstly, CNTs were decorated with a catalytically active Ni–P alloy via electroless plating (Ni–P@CNTs). Then, the Ni–P@CNTs were filled and anchored onto the framework of NF via electroplating to synthesise a self-supporting electrode (Ni–P@CNTs/NF). The Ni–P@CNTs/NF exhibited an excellent catalytic performance toward the hydrogen evolution reaction (HER) in 1 M KOH electrolyte, with an overpotential of 53 mV at 10 mA cm−2, a small Tafel slope of 101.56 mV dec−1 and excellent long-term durability. This facile and effective strategy might provide a new path to the design of self-supporting electrodes with enhanced HER catalytic.

Ultra-thin pine tree-like MoS2 nanosheets with maximally exposed active edges terminated at side surfaces on stainless steel fiber felt for hydrogen evolution reaction

High active edge sites guarantee MoS2 as a promising electrocatalyst alternative for the costly Pt based materials. However, the inherent high surface energy nature of the layer edges thermodynamically blocks the large scale synthesis, and meanwhile poses instability problems. In this work, vertically grown ultra-thin MoS2 nanosheets with a large proportion of exposed edges on commercially available 316L stainless steel fiber felts (SSF) via a simple one-step kinetically controlled hydrothermal process is reported aiming for electrocatalytic H2 production. Notably, the synthesized MoS2 nanosheet presents a three dimensional pine tree-like structure featured by the maximally exposed active edges toward side surfaces. Abundant gaps between the MoS2 nanosheets together with impressive super-hydrophilic property assure the large density of effective edge sites that accessible to electrochemical reaction and the rapid desorption of H2 products, and thus high intrinsic hydrogen evolution reaction (HER) activity. In addition to those electrochemically desired properties, the reliable contact of the MoS2 sheet on the SSF substrate together with the low price, porosity, high conductivity and high chemical corrosion resistance properties of the SSF substrate guarantee the MoS2/SSF electrode as an efficient and durable HER electrode in both strong acidic and alkaline medium for potential commercial applications.

Hydrazine-assisted electrochemical hydrogen production by efficient and self-supported electrodeposited Ni-Cu-P@Ni-Cu nano-micro dendrite catalyst

The emergence of high-performance noble metal-free electrodes in water splitting operations to produce hydrogen is of paramount importance to generate new energy in the future. The oxygen evolution reaction (OER) in water splitting is a slow reaction that consumes much energy to produce hydrogen, and generally, replacing an anodic reaction with less thermodynamic potential can significantly improve the efficiency of hydrogen production. The hydrazine oxidation reaction (HzOR) can be a great alternative to OER. We describe the fabrication of Ni-Cu-P@Ni-Cu nano-micro dendrite using a simple electrodeposition method. The developed Ni-Cu-P@Ni-Cu is used as a bifunctional electrode for hydrogen evolution reaction (HER) and HzOR. The high active electrochemical area, the porous structure and the penetration of electrolyte into the pores, the synergistic effect between Ni and Cu, and the rapid separation of the bubbles created from the surface led to the creation of an electrode with excellent electrocatalytic activity. The HER and HzOR processes required only -70 mV vs.RHE and 3.88 mV vs.RHE potentials in 1.0 M KOH and 1.0 M KOH + 0.5 M N2H4, respectively, to generate a current density of 10 mA.cm−2. Also, a very low potential of 125 mV was required in the hybrid overall water electrolysis system. This study presents a new, cost-effective, versatile, and industrial strategy to fabricate three-dimensional electrocatalysts.

Tuning the electronic structure of NiCoP arrays through V doping for pH-universal hydrogen evolution reaction electrocatalyst

The exploration of cost-effective, high-performance, and stable electrocatalysts for the hydrogen evolution reaction (HER) over wide pH range (0–14) is of paramount importance for future renewable energy conversion technologies. Regulation of electronic structure through doping vanadium atoms is a feasible construction strategy to enhance catalytic activities, electron transfer capability, and stability of the HER electrode. Herein, V-doped NiCoP nanosheets on carbon fiber paper (CFP) (denoted as Vx-NiCoP/CFP) were constructed by doping V modulation on NiCoP nanosheets on CFP and used for pH-universal HER. Benefiting from the abundant catalytic sites and optimized hydrogen binding thermodynamics, the resultant V15-NiCoP/CFP demonstrates a significantly improved HER catalytic activity, requiring overpotentials of 46.5, 52.4, and 85.3 mV to reach a current density of 10 mA·cm−2 in 1 mol·L−1 KOH, 0.5 mol·L−1 H2SO4, and 1 mol·L−1 phosphate buffer solution (PBS) electrolytes, respectively. This proposed cation-doping strategy provides a new inspiration to rationally enhance or design new-type nonprecious metal-based, highly efficient, and pH-universal electrocatalysts for various energy conversion systems.

Facile synthesis of MoS2 nanosheets-deposited TiO2 nanotubes array electrode for enhanced electrocatalytic hydrogen evolution reaction

MoS2 nanosheets were fabricated by ultrasonication of bulk MoS2 and TiO2 nanotubes array (TNA) was formed on Ti foil via anodization method. Using facile and binder-free electrophoretic technique, MoS2 nanosheets were deposited on the TNA as high surface area and well-ordered support to fabricate the MS/TNA electrode. In electrocatalytic hydrogen evolution reaction (HER), the MS/TNA indicated a low onset potential and overpotential of 85 mV at current density of −10 mA/cm2 with Tafel slope of 39 mV/dec. Furthermore, after 1000 cycles, the MS/TNA displays high stability in HER. Our results demonstrated that the MoS2 nanosheets on the TNA provide more active sites while the ordered tubular TNA support creates straight pathways for electron transport toward MoS2 nanosheets with improved interaction of the electrolyte and electrode in HER. This work introduces the MS/TNA as an efficient and cost-effective electrode for electrocatalytic production of hydrogen.

VSe2 quantum dots with high-density active edges for flexible efficient hydrogen evolution reaction

Two-dimensional (2D) metallic transition metal dichalcogenides (TMDCs) with large specific surface areas and high conductivities are promising catalysts for electrocatalytic hydrogen production. The highly active edges of the 2D metallic TMDCs are the desirable catalytic sites for the hydrogen evolution reaction (HER). Herein, the vanadium diselenide (VSe2) quantum dots with high-density edge sites are prepared by tip sonication of the self-detached VSe2 nanosheets. The spontaneously released VSe2 nanosheets, without chemical-involved transfer, offer a noncontaminated catalyst for HER. Compared to the VSe2 nanosheets, VSe2 quantum dots with a high density of active edges present a significant enhancement of the electrocatalytic performance. The reduced overpotential and transfer resistance indicate the lower Gibbs free energy and faster faradic process of the VSe2 quantum dots for HER. The active edge sites of VSe2 quantum dots show improved catalytic properties in thermodynamic and kinetic aspects. The VSe2 quantum dots loaded on a carbon cloth could be used as a flexible electrode for HER. This work provides an effective way to regulate the defects of the 2D TMDCs for high-performance HER catalysts and also offers a catalyst for flexible HER.

Ultra-thin CoS2 nanosheets synthesized by one-step hydrothermal process for hydrogen evolution

Rationally designing and synthesizing nanostructures with increased density of active sites are an effective route to enhance the hydrogen evolution reaction (HER) activity of electrocatalysts. In this work, a simple one-step hydrothermal method was used to synthesize cobalt disulfide (CoS2) nanosheets on the stainless-steel fiber (SSF) felt substrate, by which the thickness of CoS2 nanosheets can be sensitively tuned by thiourea concentration in reactant precursors. Especially, the CoS2 nanosheets synthesized under a thiourea concentration of 0.083 M present an ultra-thin thickness of about 10 nm with abundant gaps between the nanosheets. Such morphology with large effective surface area together with superhydrophilic property assures it an effective HER electrode, showing an overpotential of − 290.6 mV at 10 mA cm−2 and a Tafel slope of 74.21 mV dec−1 over other samples synthesized under higher thiourea concentrations. Chronoamperometric test also shows excellent HER durability by the assistance of chemical-stable SSF substrate.

Electrodeposited rhenium–cobalt alloy with high activity for acidic hydrogen evolution reaction

The development of high-performance electrodes for hydrogen evolution reaction (HER) is essential for commercialization of water electrolyzers. Among the promising candidate for HER catalyst, Re and its oxide display an optimal hydrogen binding energy to that of Pt. Nevertheless, only a few studies have reported the acidic HER catalysts with the high overpotentials (>100 mV at –10 mA cm–2). Furthermore, Re transition metal alloy for the acidic HER catalyst have rarely been reported. Herein, we report a CoRe alloy catalyst for the acidic HER, which was fabricated by electrodeposition on carbon paper (CP) by controlling the electrodeposition. The optimized CoRe/CP electrode exhibited a higher HER activity than those of the other Re-based catalysts with an overpotential of 45.1 mV at −10 mA cm–2. The activation energy for the HER of CoRe/CP, which was calculated from the Arrhenius plot, demonstrated a lower value of 8.99 kJ mol–1 K–1.

Recasting Ni-foam into NiF2 nanorod arrays via a hydrothermal process for hydrogen evolution reaction application.

A promising electrode for hydrogen evolution reaction (HER) has been prepared via a reduction process to form NiF2 nanorod arrays directly grown on a 3D nickel foam. We reveal NiF2@Ni nanorod arrays for a stable hydrogen evolution reaction (HER) application. The computational analysis for H2O, OH and H and experimentally in aqueous KOH endow considerable shift in Fermi levels for Ni (111) unlike for NiF2(110) on account of an effective coalition ofp-orbitals of fluorine andd-orbitals of Ni in NiF2, NiF2 under pinning the reduced overpotential of 172 mV at 10 mA cm-2compared to Ni (242 mV) in same electrolyte. The electrocatalytic mechanism has been proposed using density functional theory (DFT) and is found in well accordance with the experimental findings of the present study. The preparation of self-grown porous nanostructured electrodes on the 3D nickel foam via a displacement reaction is possibly valuable for other metal halides for energy storage and conversion applications as these materials have inherently smaller overpotentials.

Pd nanocluster-decorated CoFe composite supported on nitrogen carbon nanotubes as a high-performance trifunctional electrocatalyst

Rational design and synthesis of low-cost trifunctional electrocatalysts with improved stability and superior electrocatalytic activity for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are highly desirable but remain as the bottlenecks at the current state of technology. In this paper, the cobalt-iron (Co–Fe) composite supported on nitrogen-doped carbon nanotubes (CoFe composite/NCNTs) is synthesized. The intrinsic OER and HER catalytic activities of this CoFe composite/NCNTs composite are significantly improved with palladium (Pd) nanocluster decoration [Pd-coated (CoFe composite/NCNTs)]. The as-prepared Pd-coated (CoFe composite/NCNTs) catalyst exhibits excellent trifunctional electrocatalytic activity and stability due to the interfacial coupling between Pd and (CoFe composite/NCNTs). This catalyst is successfully employed in the water electrolysis cell as both OER and HER electrode catalysts, flexible rechargeable Zn-air battery as the bifunctional ORR and OER electrode catalyst. The cell voltage of this catalyst-coated electrodes requires only 1.60 V to achieve 10 mA cm−2 current density for water electrolysis cell, which is comparable to and even better than that of Pt/C and Ir/C based cell. The primary Zn-air battery using this catalyst shows a constant high open-circuit voltage (OCV) of 1.47 V and a maximum power density of 261 mW cm−2 in the flooded mode configuration. Most importantly, a flexible Zn-air battery with this catalyst runs very smoothly without a change in voltage gap during flat, bending, and twisting positions.

Engineering iron phosphide-on-plasmonic Ag/Au-nanoshells as an efficient cathode catalyst in water splitting for hydrogen production

Constructing highly active electrocatalysts for hydrogen evolution reaction (HER) have drawn considerable attention recently. However, how to design nanostructured electrocatalysts with enhanced catalytic performances is still a challenge. Herein, plasmonic Ag/Au hollow porous nanoshells decorated with porous Fe2P thin layers (denoted as Ag/Au-HPNSs@PFP) are fabricated, in which porous Fe2P (PFP) thin layers are derived from pyrolysis and phosphidation of MIL-100(Fe) coated on plasmonic Ag/Au hollow porous nanoshells (Ag/Au-HPNSs) and the high porosity of the HER-active Fe2P, along with plasmonic enhancement of the Ag/Au hollow porous nanoshells, facilitates hydrogen evolution and electron transport, and accordingly boosts the electrocatalytic HER performance. When applied as a HER electrode, the hybrid electrocatalyst displays an onset overpotential of only 108 mV, satisfactory stability, and enhanced performance for hydrogen evolution under visible light, ascribing to electron interactions between Fe and P and synergistic effects of porous Fe2P and plasmonic Au/Ag hollow porous nanoshells.

Fabrication of Iron Phosphide Nanoparticle/Carbon Paper Electrodes Via Electrophoretic Deposition for HER Catalysis

As a renewable energy source to replace traditional fossil fuels, hydrogen is a promising sustainable energy carrier due to its eco-friendly nature and high energy density. Although Pt-based materials are widely used as catalysts for generating hydrogen through water electrolysis because of their high catalytic activity, Pt is expensive, and its scarcity hinders the commercialization of large-scale hydrogen production. The development of alternative low-cost materials with low hydrogen evolution reaction (HER) overpotential is the key to achieve low price and highly efficient hydrogen generators such as proton-exchange membrane water electrolysis (PEMWE). Among the numerous candidates of earth-abundant materials, transition metal-based phosphides (TMPs) are suitable for HER applications due to their low toxicity, high electrical conductivity, and catalytic activity. Especially, FeP is in the spotlight as a HER catalyst due to its high catalytic activity in solutions with a wide pH range, and this is a competitive material for large-scale commercial production of hydrogen, since Fe is one of the most abundant elements on earth.In this study, we synthesized the colloidal FeP nanoparticles (NPs) via a hot injection process, so that the pre-synthesized Fe NPs can be converted to FeP NPs through the phosphorization reactions by various phosphorus sources (trioctylphosphine, triphenylphosphite (TPP), tris(diethylamino)phosphine, and tri-n-butylphosphine). Different HER activities were induced by the phase transformation of NPs over the controlled reaction time for the NP samples synthesized with each phosphorus precursor. The FeP synthesized using TPP achieved excellent HER activity with an overpotential of 76 mV at 10 mA cm-2 in 0.5 M H2SO4 as measured by drop casting the catalyst on Ti foil. In terms of the fabrication for the efficient HER electrode, the prepared FeP NPs were deposited on the carbon paper (CP) via electrophoretic deposition (EPD), which is a suitable method for the fabrication of NP films that can be used for various electronic applications. Different morphologies and catalytic activities of the FeP/CP samples were derived by controlling EPD parameters such as mixing ratio of solvents, NP concentration, and deposition voltage. The optimized EPD process lead to excellent HER activity of the FeP/CP with an overpotential of 38 mV and 91 mV at 10 mA cm-2 in 0.5 M H2SO4 and 1 M KOH, respectively. The maximum activity of the catalyst was mainly attributed to the large active surface area and low charge transfer resistance due to the strong contact between the NPs and CP. A PEMWE single cell with the FeP/CP cathode achieved 1.2 A cm-2 at cell voltage of 2.0 V. This study of the EPD procedure for fabricating the NP film from the colloidal NP catalysts contributes to advance manufacturing of HER electrodes for efficient hydrogen generation through water electrolysis.