Preparation,characterization and hydrogen production performance of MoPd deposited carbon felt/Mo electrodes

Mo-coated carbon felt (C) supporting material modified by electrochemical deposition of trace amounts of MoPd binary composites having various metal ratios and characterized using various techniques. To our best knowledge, these materials is being reported firstly. The hydrogen evolution activity of the electrodes tested in 1 M KOH solution using electrochemical techniques. It shown that MoPd modified electrodes have large surface area, which is very beneficial for the rate of hydrogen evolution reaction (HER). Pd and Mo metals almost homogeneously distributes over the surface and no local aggregations are appeared. The loading of MoPd binary deposits over the Mo-coated C supporting material enhances the rate of the HER more and more when compared to the base substrate. The hydrogen evolution performance of the composites is depending on the metal ratios. The enhanced current density at the C/Mo-Mo₅₀Pd₅₀ electrode at ?1.60 V(Ag/AgCl) is 79.1% with respect to the C felt and 48.1% with respect to the C/Mo modified supporting material. The reduction in resistance related to hydrogen gas releasing at 100 mV overpotential was 97.2% and 58.6% with respect to bare C felt and C/Mo supporting material. The high hydrogen releasing performance of the PdMo-modified electrocatalysts related to intrinsic catalytic activities of Pd and Mo, a possible synergism between these metals and enhanced real surface area of the electrode. The C/Mo-Mo₅₀Pd₅₀ electrode has excellent electrochemical and physical stability during the long time electrolysis. Therefore, it is expected that the procedure applied here contribute to literature since the modifying C support by an active metal provides activation of electrocatalysts. Due to superior properties, we can suggest C/Mo-Mo₅₀Pd₅₀ electrode as promising cathode material for industrial water electrolysis which can reduces the energy input.     

Benign synthesis of robust nickel thin films as stretchable electrodes for electrochemical hydrogen evolution reaction

In this paper, we fabricate the nickel thin film on copper and acrylonitrile-butadiene-styrene (ABS) polymer substrate by means of electroless deposition method and compare their hydrogen evolution reactions (HER). Ni deposited on both specimens reveals the preferred crystalline orientation of (111) plane and petal like topography. The HER activity and durability of the Ni electrode is investigated through linear sweep voltammetry and Tafel polarization studies. We measure the current density value of the first cycle at 350 mV vs. RHE and found that nickel deposited on the ABS polymer and a copper substrate exhibits the cathode current density of 29 and 4 mA cm^?2 respectively. After 1000 cycles, 61% of HER activity has been retained in nickel deposited on the ABS polymer whereas nickel plated on the copper strip retains only 20% of HER activity. A small Tafel slope of 82 and 144 mV dec^?1 is observed for nickel deposited on the ABS polymer and copper samples respectively.     

Mn–Mo–W-oxide anodes for oxygen evolution during seawater electrolysis for hydrogen production: Effect of repeated anodic deposition

MnMoW-triple oxide catalyst for chlorine-less oxygen generating electrodes from seawater electrolysis were prepared by repeated anodic deposition of their oxides on Ti/IrO₂ substrate. The durability of the electrodes were examined by electrolysis in 0.5 M NaCl solution at current density of 1000 Am⁻² and compared with their corresponding electrodes that were prepared by continuous anodic deposition. The electrodes repeatedly and continuously deposited for 90 min kept the oxygen evolution efficiency higher than 99% for 2600 h and 120 h of electrolysis, respectively. The improvement in the electrode durability by repeated deposition was attributed to the formation of single phase oxide deposits of MnMoW-oxides with optimized thickness, composition and structural water content, which enables the reduction of the electrode overpotential for the oxygen evolution reaction and increase overall stability and adhesion of the oxide deposits to Ti/IrO₂ substrate. A mechanism for oxygen evolution at the anode surface during electrolysis was proposed.     

Noble fabrication of Ni–Mo cathode for alkaline water electrolysis and alkaline polymer electrolyte water electrolysis

Among the catalysts for hydrogen evolution reaction (HER) in alkaline media, Ni–Mo turns out to be the most active one. Conventional preparations of Ni–Mo electrode involve repeated spraying of dilute solutions of precursors onto the electrode substrate, which is time-consuming and usually results in cracking and brittle electrodes. Here we report a noble fabrication of Ni–Mo electrode for HER. NiMoO₄ powder was synthesized and used as the precursor. After reduction in H₂ at 500 °C, the NiMoO₄ powder layer was converted to a uniform and robust electrode containing metallic Ni and amorphous Mo(IV) oxides. The distribution of Ni and Mo components in this electrode is naturally uniform, which can maximize the interaction between Ni and Mo and benefit the electrocatalysis. The thus-obtained Ni–Mo electrode exhibits a very high catalytic activity toward the HER: the current density reaches 700 mA/cm² at 150 mV overpotential in 5 M KOH solution at 70 °C. This new fabrication method of Ni–Mo electrode is not only suitable for alkaline water electrolysis (AWE), but also applicable to the alkaline polymer electrolyte water electrolysis (APEWE), an emerging technique for efficient production of H₂.     

Investigation of noble metal loading CoWZn electrode for HER

It is important to metal deposition on the electrode surface to increase the electrocatalytic activity of the electrodes. CoWZn coated the graphite rod was used to prepare the cathode electrode. Moreover, then Pt and Ru metals were deposited on the electrode surface. These electrodes were named as CoWZnPt and CoWZnRu. Cyclic voltammetry, electrochemical impedance spectroscopy, and potentiodynamic polarization techniques were used for characterization of electrodes in alkaline media. Hydrogen evolution efficiency was determined by accumulated of hydrogen gas. The catalytic activity for hydrogen evolution reaction of CoWZn, CoWZnPt, and CoWZnRu electrodes was compared. It was reported that modification of the CoWZn electrode with low amounts of Ru enhances the HER activity of the electrodes. The enhancement in the hydrogen evolution activity of the electrodes was attributed to the increase in their real surface area and/or a possible synergistic effect between Co, W, Zn and Ru as well as the well-known intrinsic catalytic activity of Ru.     

Pt/Fe-NF electrode with high double-layer capacitance for efficient hydrogen evolution reaction in alkaline media

The electrode with high catalytic activity, low hydrogen overpotential and low cost is desired for hydrogen evolution reaction (HER) via electrocatalytic water splitting. In this study, Pt/Fe-Ni foam (Pt/Fe-NF) electrode was synthesized via cathodic electrodeposition followed by impregnation deposition. Physical and electrochemical properties of Pt/Fe-NF, NF and Pt/NF electrodes were characterized by various techniques. The Pt/Fe-NF electrode exhibited better electrochemical activity for HER under alkaline condition than those of Pt/NF and NF electrodes, owing to the introduction of zero valences Pt and Fe onto the NF, and synergetic effect resulted from the formation of Fe-Ni alloy. Furthermore, Pt/Fe-NF electrode showed extremely high double-layer capacitance (69.1 mFcm^?2), suggesting high active sites for the Pt/Fe-NF. Tafel slope of Pt/Fe-NF was 59.9 mV dec^?1, indicating that the Volmer-Heyrovsky HER mechanism was the rate-limiting step. The Pt/Fe-NF electrode with great electrocatalytic activity is a promising electro-catalyst for industrial hydrogen production from alkaline electrolyte.     

Enhancement of hydrogen evolution at cobalt-zinc deposited graphite electrode in alkaline solution

Thin Co layers were electrochemically deposited on a graphite electrode at different deposition current densities and thicknesses. After determining the best deposition conditions for hydrogen evolution (deposition current density and thickness), co-deposits of Co with Zn were prepared on the graphite electrode. The binary coatings prepared on the graphite electrode (CoZn) were etched in a concentrated alkaline solution (30% NaOH) to produce a porous and electrocatalytic surface suitable for use in the hydrogen evolution reaction (HER). After the leaching process, a low amount of Pt was deposited onto the etched CoZn deposit in order to further improve the catalytic activity of the electrode for the HER. The HER activity is assessed by recording cathodic current-potential curves, electrochemical impedance spectroscopy (EIS) and electrolysis techniques. Chemical composition of layers after alkaline leaching was determined by energy dispersive X-ray (EDX) analysis. The surface morphologies of coatings were investigated by scanning electron microscopy (SEM). It was found that, the HER activity of coatings depends on the metal ratio of Co and Zn, deposition current density and the thickness of coatings. The alkaline leached CoZn coating has a compact and porous structure as well as good electrocatalytic activity for the HER in alkaline media. Moreover, deposition of a low amount of Pt over the CoZn can further enhance its hydrogen evolution activity.     

Electrochemical growth of MoSx on Cu foam: A highly active and robust three-dimensional cathode for hydrogen evolution

In this paper, we report a highly active and robust three-dimensional (3D) Cu foam@MoS_x electrode for electrocatalytic hydrogen evolution reaction (HER) prepared by a simple and controllable electrochemical deposition method. Highly conductive Cu foam scaffold with exposed 3D frameworks can not only ensure an intimate interface for facilitate a fast electron transfer but also render the deposited amorphous MoS_x with abundant exposed active sites and large contact area for electrolyte diffusion. As a result, the optimized Cu foam@MoS_x electrode exhibits high activity for electrocatalytic H₂ evolution in 0.5 M H₂SO₄, the required overpotentials to reach current densities of 10 and 100 mA cm^?2 are 200 and 250 mV, respectively. Moreover, the Cu foam@MoS_x electrode shows no obvious deactivation after 2000 potential cycling and also retains its outstanding electrocatalytic activity after 10 h bulk electrolysis for H₂ evolution due to the robust adhesion of MoS_x. This work provides a new strategy to the development of highly active HER electrocatalyst by integrating high-surface-area and conductive substrate and the favorable surface structures of active components.     

Enhanced catalytic activity towards hydrogen evolution on polythiophene via microstructural changes

The discovery of poly(2,2′-bithiophene) (PBTh) as a photo-electrochemical catalyst for the hydrogen evolution reaction (HER) presents a novel electrode material for the transition to a sustainable hydrogen energy economy. Nonetheless, it remains limited by a low hydrogen evolution rate. We here investigate two methods in which to increase the catalytic activity of PBTh: using humidity for alternative templating and substrate roughening. It was found that exposure of the oxidant solution to humidity prior to polymerisation causes the formation of new microstructures that was found to increase catalytic activity of the PBTh film by over four times, from 14 to 57 µA cm^-2. It was also found that control of the atmospheric environment proved critical. In contrast, the roughening of the substrate did not consistently lead to an increase in performance and was attributed to poor adhesion and electrical contact of the film to the substrate. During these tests however, a photo-electrocatalytic current of 150 μA cm^?2 was recorded in pH 7.0 and an underpotential of 0.12 V on an un-roughened PBTh sample. This represents the highest reported value for PBTh thus far and a significant achievement for its further development towards a low-cost and efficient HER catalyst.     

Gold‐supported activated NiZn coatings: hydrogen evolution and corrosion studies

Gold‐supported Raney‐type NiZn coatings were prepared on a thin Ni film‐modified copper substrate (Cu/Ni/NiZn‐Au). The hydrogen evolution activity, time stability and corrosion behaviour of the electrode was investigated in 1 M KOH solution by electrochemical, microscopic and spectroscopic technique. It was found that Au‐modified activated coatings exhibits good hydrogen evolution activity, electrochemical and physical stability as well as corrosion resistance. The enhanced hydrogen evolution activity of the Au‐modified electrode was related to the larger available surface area and/or a possible synergistic effect between the metals. Copyright © 2017 John Wiley & Sons, Ltd.     

Electrochemical fabrication of Ni–Mo nanostars with Pt-like catalytic activity for both electrochemical hydrogen and oxygen evolution reactions

Synthesis of electrocatalysts with excellent performance for hydrogen and oxygen evolution are the main challenges for production of hydrogen by electrochemical water splitting method. Here, Ni–Mo nanostars were created by electrochemical deposition process at different morphologies and their electrocatalytic behavior was studied for hydrogen and oxygen evolution reactions in 1.0 M KOH solution. Increased electrochemically active surface area due to the nanostars formation, improved intrinsic electrocatalytic activity, increased surface wettability, as well as being binder-free during electrode production, resulted in excellent electrocatalytic behavior. For optimized condition, 60 mV and 225 mV overpotential are needed for generating the current density of 10 mA.cm-² in HER and OER process respectively in the alkaline medium. The lower slope of the electrode compared to the other electrodes also indicated that the kinetics of HER on the surface of the electrode was better. Also, there was very little change in the potential during the stability test, indicating the excellent electrocatalytic stability of the synthesized electrode. The present study introduces a rational, cost-effective and binder-free method for the synthesis of high performance electrocatalysts.     

Highly active nanostructured water oxidation catalyst electrodeposited from Co(cyclam) complex

The water soluble molecular complex [Co(cyclam)(ClO₄)]ClO₄ (cyclam = 1,4,8,11-tetraazacyclotetradecane) is utilized as a precursor for deposition of highly active cobalt based nanostructured material on the electrode surface upon electrooxidation. The electrolysis of the complex at +1.1 V vs Ag/AgCl in 0.1 M potassium phosphate at pH 12 leads to the formation of a nanoporous Co(II) hydroxide/phosphate thin film on the printed carbon electrode. The deposited surface was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). The modified electrode (Co-PCE-12) is stable for more than 34 h during the continuous electrolysis. The modified electrode exhibits a high water oxidation catalytic activity of 6.5 mA cm^?2 at an overpotential of 580 mV (0.9 V vs Ag/AgCl (3 M KCl) at pH 12) with 98% Faradaic yield.     

Electrochemical preparation and characterization of C/Ni–NiIr composite electrodes as novel cathode materials for alkaline water electrolysis

The binary NiIr coatings as novel and effective catalysts were electrochemically prepared on a Ni-modified carbon felt electrode (C/Ni–NiIr) in view of their possible application as cathode materials for the alkaline water electrolysis. The surface morphology and chemical composition of the electrodes were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. Their hydrogen evolution activity was assessed by electrochemical techniques. It was found that, the preparation of NiIr co-deposits on the Ni-modified C substrate enhances the hydrogen evolution activity. The electrodes have wide space, which is an advantage for diffusion of ions and hydrogen bubbles through inner zones and reduction of diffusion resistance. The high hydrogen evolution activity of the C/Ni–NiIr electrode was mainly attributed to the finer surface structure, high surface area and the higher numbers of the catalytically active centers.     

Influence of electrodeposition parameters of Ni–W on Ni cathode for alkaline water electrolyser

In this study, different Ni–W coatings, obtained by cheap and technologically simple electrodeposition method, were examined as potential electrocatalysts for the hydrogen evolution reaction (HER). All electrodepositions were done on a Ni mesh substrate from ammoniacal-citrate bath containing different concentrations of Na₂WO₄. The influence of deposition parameters, such as deposition current density, pH and composition of ammoniacal-citrate bath on electrocatalytic activity of obtained Ni–W coatings toward HER was examined by polarization curve measurements in 6 M KOH at room temperature. The morphology and tungsten content of the Ni–W coatings were investigated by means of SEM and EDS analysis. All investigated electrodes have shown high electrocatalytic activity for the HER. The samples obtained at higher deposition current densities had the lowest overvoltage for the HER. It has been shown that the plating bath pH value is very important parameter in obtaining active coatings. Results of the analysis of polarization curves, morphology of deposited Ni–W coatings and the content of tungsten in the coatings, indicate that the surface roughness of the coatings is responsible for their catalytic activity towards HER.     

The effect of 3D silver nanodome size on hydrogen evolution activity in alkaline solution

Three-dimensional (3D) Ag nanodomes (AgNDs) having different sizes (400, 800, 1200 and 1600 nm) were fabricated using combination of nanosphere lithography and soft lithography. The surface structures of 3D assembled latex particles, nanovoids and metal nanodomes (ND) were examined using scanning electron microscopy (SEM). Their heights and widths analyses were performed with the help of atomic force microscopy (AFM). The effect of diameter of the NDs on their hydrogen evolution activity was examined in 6 M KOH solution at 298 K using electrochemical techniques. Their activities were compared with the activity of bulk Ag electrode. The preparation of 3D-AgNDs having various diameters and examination of their size effects on the water splitting activity have not been studied yet and are being reported firstly. It was found that very well-structured and very uniformly distributed NDs can be fabricated using this procedure. AgNDs exhibit higher hydrogen evolution activity with respect to bulk Ag. Their hydrogen evolution activity depends on their diameters; 1200 nm NDs were the best among them. The current density at ?1.40 V(Ag/AgCl) which is proportional to the rate of hydrogen releasing reaction increases from 0.70 mA cm^?2 to 44.13 mA cm^?2 at this ND electrode with respect to the bulk Ag electrode. At the same 3D-AgNDs electrode and potential, the resistance against the HER reduces from 148.7 Ω cm² to 1.12 Ω cm² (99.6%) by comparing with the bulk Ag electrode. The average surface roughness factors of bulk Ag, 400 nm, 800 nm, 1200 nm and 1600 nm AgNDs are 8, 123, 100, 291 and 176, respectively. The superior hydrogen evolution performance of this electrode is related to its well-structured surface and large real surface area.     

Efficient hydrogen evolution performance of phase-pure NiS electrocatalysts grown on fluorine-doped tin oxide-coated glass by facile chemical bath deposition

The production of hydrogen, the future fuel, on stable, efficient, and robust electrocatalysts represents an attractive approach for the conversion and storage of carbon-free energy resources. In this study, earth-abundant nickel sulfide (NiS) electrocatalyst were grown on fluorine-doped tin oxide (FTO) substrate by a simple and cost-effective chemical bath deposition for hydrogen evolution reaction (HER). Energy dispersive X-ray analysis and X-ray photoelectron spectra indicated the presence of highly pure NiS. The HER performance of the catalyst was examined in alkaline solution (1.0 M NaOH; pH = 13.5). Notably, NiS film prepared at 100 °C demonstrated superior HER activity with an overpotential of 290 mV to afford a current density of 10 mA/cm² and a Tafel slope of 143.4 mV/dec which are among the promising results obtained for sulfide-based HER electrocatalysts. The catalyst exhibited 100% faradaic efficiency and electrochemical stability which indicate its potential as noble-metal-free HER electrocatalyst.     

Electrocatalytic oxidation of hydrogen peroxide on the surface of nano zeolite modified carbon paste electrode

This study investigated the use of synthesized nanozeolite Y to prepare modified carbon paste electrode for electrocatalytic oxidation of hydrogen peroxide. In order to prepare the modified electrodes, the nickel ions were doped to Y zeolite framework through ion exchange mechanism and the electrochemical behaviour of the proposed modified electrode was studied using the cyclic voltammetry technique. The obtained results revealed that modified carbon paste electrode in the form of Ni/NiYCPE is the best electrode for the oxidation of hydrogen peroxide in the alkaline media. The hydrogen peroxide transfer coefficient (α) and the current density were calculated as 0.54 and 6.7 mA/cm², respectively. The catalytic rate constant (K) for this electrocatalytic reaction was calculated through the chronoamperometric technique (K = 0.43 × 10⁴ cm²s^?1mol^?1).     

Three dimensional assembly of electrocatalytic platinum nanostructures on reduced graphene oxide – An electrochemical approach for high performance catalyst for methanol oxidation

By means of co-electrodeposition, we fabricated 3D assembly of Pt nanostructures with dominant (100) plane on reduced graphene oxide (rGO) modified graphite electrode. The strong metal-support interaction at the atomic level makes the nanostructure highly durable and this modified electrode exhibited high electrocatalytic activity towards methanol oxidation. It has been found that the morphology, active site and the electrochemical activity of Pt are highly dependent on the substrate and the number of electrochemical cycling used for the deposition. rGO-Pt composite deposited using one cycle showed a high mass activity of 2.54 A/mg at 0.67 V for methanol oxidation in acidic condition and 1.84 A/mg at ?0.03 V in alkaline medium. This simple and single step approach using electrodeposition to grow the morphology controlled Pt nanostructure on rGO, will aid in the development of active and stable catalyst for fuel cell applications.     

Dimensionally stable NiFe@Co/Ti nanoporous electrodes by reactive deposition for water electrolysis

The development of efficient and dimensionally stable electrode plates is of a significant challenge for the oxygen evolution reaction in the industrial water electrolysis process. In this work, structurally stable electrode plates are developed based on the nanostructured NiFe catalysts on highly porous and dimensionally stable Co reactive deposited on Ti substrates, NiFe@Co/Ti. SEM analysis shows the hierarchically structured micro- and nano-porous structure of the Co electrode on Ti substrates by reactive deposition route. The surface area of the reactive deposited Co is 3 times larger than that of the conventional electrodeposited Co electrode, providing highly porous and stable base for the subsequent deposition of NiFe electrocatalysts. The as-prepared NiFe@Co/Ti electrode exhibits high catalytic activity towards oxygen evolution in alkaline solutions, achieving an onset potential of as low as 1.44 V (η = 210 mV) and delivering a current of 10 mA cm^?2 at an overpotential of 0.26 V. Most importantly, the electrode shows excellent stability with negligible degradation under the discharge current density at 100 mA cm^?2 for 100 h, demonstrating the practical applicability of the NiFe@Co/Ti nanostructured electrodes for industrial scale water electrolysis.     

Synthesis and characterisation of platinum–cobalt–manganese ternary alloy catalysts supported on carbon nanofibers: An alternative catalyst for hydrogen evolution reaction

A systematic method for obtaining a novel electrode structure based on PtCoMn ternary alloy catalyst supported on graphitic carbon nanofibers (CNF) for hydrogen evolution reaction (HER) in acidic media is proposed. Ternary alloy nanoparticles (Co0.6Mn0.4 Pt), with a mean crystallite diameter under 10 nm, were electrodeposited onto a graphitic support material using a two-step pulsed deposition technique. Initially, a surface functionalisation of the carbon nanofibers is performed with the aid of oxygen plasma. Subsequently, a short galvanostatic pulse electrodeposition technique is applied. It has been demonstrated that, if pulsing current is employed, compositionally controlled PtCoMn catalysts can be achieved. Variations of metal concentration ratios in the electrolyte and main deposition parameters, such as current density and pulse shape, led to electrodes with relevant catalytic activity towards HER. The samples were further characterised using several physico-chemical methods to reveal their morphology, structure, chemical and electrochemical properties. X-ray diffraction confirms the PtCoMn alloy formation on the graphitic support and energy dispersive X-ray spectroscopy highlights the presence of the three metallic components from the alloy structure. The preliminary tests regarding the electrocatalytic activity of the developed electrodes display promising results compared to commercial Pt/C catalysts. The PtCoMn/CNF electrode exhibits a decrease in hydrogen evolution overpotential of about 250 mV at 40 mA cm⁻² in acidic solution (0.5 M H₂SO₄) when compared to similar platinum based electrodes (Pt/CNF) and a Tafel slope of around 120 mV dec⁻¹, indicating that HER takes place under the Volmer-Heyrovsky mechanism.