Electrocatalysts For Hydrogen Production Research Articles

Robust Hydrogen-Evolving Electrocatalyst from Heterogeneous Molybdenum Disulfide-Based Catalyst

Molybdenum disulfide-based layered materials are promising electrocatalysts for hydrogen production from water electrolysis if their catalytic performance can be further improved by increasing the ...

Plasma-assisted synthesis of hierarchical NiCoxPy nanosheets as robust and stable electrocatalyst for hydrogen evolution reaction in both acidic and alkaline media

Transition metal phosphides are emerging non-noble metal electrocatalysts for hydrogen evolution reaction (HER) in water splitting. Herein, porous nickel cobalt phosphide nanosheet arrays with hierarchical structure were synthesized on carbon cloth (NiCoxPy-P/CC) as a robust and stable HER electrocatalyst by a facile approach involving electrodeposition and an effective PH3 plasma-assisted phosphorization. Owing to the unique structure with porous nanosheets composed of defect-abundant fine nanocrystals, the as-synthesized NiCoxPy/CC electrocatalyst demonstrates superior catalytic activity for HER to its thermally-phosphorized counterpart. Only at the overpotential as low as 70 (in 0.5 M H2SO4) and 42 mV (in 1 M KOH), the current density of 10 mA/cm2 is achieved for the NiCoxPy/CC, which is among the best reported values for metal phosphide electrocatalysts. Moreover, the catalyst shows satisfying long-term durability up to 24 h in both the acidic and alkaline media. The outstanding HER performance and efficient synthesis strategy for the NiCoxP-P/CC makes it a promising electrocatalyst for hydrogen production.

Interlaced rosette-like MoS2/Ni3S2/NiFe-LDH grown on nickel foam: A bifunctional electrocatalyst for hydrogen production by urea-assisted electrolysis

In targeting the most important energy and environmental issues in current society, the development of low-cost, bifunctional electrocatalysts for urea-assisted electrocatalytic hydrogen (H2) production is an urgent and challenging task. In this work, interlaced rosette-like MoS2/Ni3S2/NiFe-layered double hydroxide/nickel foam (LDH/NF) is successfully synthesized by a two-step hydrothermal reaction. Due to its unique interlaced heterostructure, MoS2/Ni3S2/NiFe-LDH/NF exhibits excellent bifunctional catalytic activity towards the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER) in 1.0 M KOH with 0.5 M urea. In a concurrent two-electrode electrolyser (MoS2/Ni3S2/NiFe-LDH/NF(+,-)), only voltage of 1.343 V is required to reach 50 mA cm−2, which is 216 mV lower than for pure water splitting. Furthermore, after 16 h of urea electrolysis in 1.0 M KOH with 0.5 M urea, the current density remains at 98% of the original value. Thus, the catalyst is not only favorable for H2 production, but also has great significance for the problem of urea-rich wastewater treatment.

Molecular Electrocatalysts for the Hydrogen Evolution Reaction: Input from Quantum Chemistry.

In the pursuit of carbon-free fuels, hydrogen can be considered as an apt energy carrier. The design of molecular electrocatalysts for hydrogen production is important for the development of renewable energy sources that are abundant, inexpensive, and environmentally benign. Over the last 20 years, a large number of electrocatalysts have been developed, and considerable efforts have been directed toward the design of earth-abundant, first-row transition-metal complexes capable of promoting electrocatalytic hydrogen evolution reaction (HER). In this context, numerical approaches have emerged as powerful tools to study the catalytic performances of these complexes. This review covers some of the most significant theoretical mechanistic studies of biomimetic and bioinspired homogeneous HER catalysts. The approaches employed to study the free energy landscapes are discussed and methods used to obtain accurate estimates of relevant observables required to study the HER are presented. Furthermore, the structural and electronic parameters that govern the reactivity, and are necessary to achieve efficient hydrogen production, are discussed in view of future research directions.

Bimetallic NiPd Nanoparticle-Incorporated Ordered Mesoporous Carbon as Highly Efficient Electrocatalysts for Hydrogen Production via Overall Urea Electrolysis

Efficient catalysts for energy conversation from wastewater and energy storage are still existing. The effective hydrogen energy production through lower energy consumption is considered as a promi...

Visible-light-enhanced electrocatalytic hydrogen production on semimetal bismuth nanorods

Controlling the compositions and morphologies of the electrocatalysts were conventionally used for improving the catalytic activities. Here, visible-light-enhanced electrocatalytic water reduction reactions on semimetal bismuth (Bi) nanorods were achieved. The Bi catalyst not only exhibited an ideal Faradaic efficiency of 98% for electrocatalytic hydrogen production, but also acted as a light absorber for improving the activity even under light irradiation up to 740 nm. As a result, the solar-to‑hydrogen conversion efficiency under simulated AM 1.5G illumination was reached to 0.82%, which is 2.7 times higher than that induced by plasmon Au nanoparticles. This conversion efficiency is attributed to the excellent solar light absorption property of Bi and the enhanced electron-transfer at the interface of Bi/electrolyte under irradiation. The low-cost Bi catalyst with the dual function could open a venue toward designing more-energy-efficient electrocatalysts for hydrogen production assisted by sunlight.

Laser-direct-writing of 3D self-supported NiS2/MoS2 heterostructures as an efficient electrocatalyst for hydrogen evolution reaction in alkaline and neutral electrolytes

Searching for low-cost widely applicable electrocatalysts for hydrogen production is very important. Here, 3D self-supported NiS2/MoS2 heterostructures were synthesized via a one-step millisecond-laser-direct-writing method; these structures exhibited excellent hydrogen evolution reaction activities over a wide pH range. The current density of 10 mA cm−2 could be reached at low overpotentials of 98 and 159 mV in alkaline and neutral electrolytes, respectively. Such an outstanding electrocatalytic performance should be attributed to the integration of the 3D self-supported nanostructures, the high conductivity of the framework, and particularly, the incalculable heterointerfaces formed between NiS2 and MoS2. This work provides a new strategy to study interfacial engineering and the mechanism of interface enhancement.

Self-Supported Ni/NiSPx Microdendrite Structure for Highly Efficient and Stable Overall Water Splitting in Simulated Industrial Environment

The design and development of non-noble metal-based bifunctional electrocatalysts for hydrogen production from catalytic electrolysis of water in industrial environments is very important for the a...

Amorphous Ni/C nanocomposites from tandem plasma reaction for hydrogen evolution

There is a growing interest in the nanostructure of metal nanoparticles encapsulated in carbon shells (M/C) to act as cost-effective and high-performance electrocatalysts for hydrogen production. Despite tremendous efforts, large-scale and controllable production of highly-active M/C nanocomposites for electrocatalysis remains a great challenge. Herein, we report a tunable and general strategy tandem plasma reaction (TPR) for manufacturing a series of carbon encapsulated Ni/C nanocomposites with different compositions. Benefiting from the synergistic effect between the conductive carbon layer and Ni nanoparticles, the electrocatalytic performance can be adjusted to an optimal state. A volcano shape dependence between electrocatalytic activity and the percentage of carbon is presented experimentally. With the simplicity and intelligence of the approach, the strategy based on tandem plasma reaction presents great potential to the preparation of extendable metal/carbon nanocomposites for versatile applications.

Scalable Production of Few-Layer Niobium Disulfide Nanosheets via Electrochemical Exfoliation for Energy-Efficient Hydrogen Evolution Reaction.

Two-dimensional (2D) niobium disulfide (NbS2) materials feature unique physical and chemical properties leading to highly promising energy conversion applications. Herein, we developed a robust synthesis technique consisting of electrochemical exfoliation under alternating currents and subsequent liquid-phase exfoliation to prepare highly uniform few-layer NbS2 nanosheets. The obtained few-layer NbS2 material has a 2D nanosheet structure with an ultrathin thickness of ∼3 nm and a lateral size of ∼2 μm. Benefiting from their unique 2D structure and highly exposed active sites, the few-layer NbS2 nanosheets drop-casted on carbon paper exhibited excellent catalytic activity for the hydrogen evolution reaction (HER) in acid with an overpotential of 90 mV at a current density of 10 mA cm-2 and a low Tafel slope of 83 mV dec-1, which are superior to those reported for other NbS2-based HER electrocatalysts. Furthermore, few-layer NbS2 nanosheets are effective as bifunctional electrocatalysts for hydrogen production by overall water splitting, where the urea and hydrazine oxidation reactions replace the oxygen evolution reaction.

Highly Electroactive Ni Pyrophosphate/Pt Catalyst toward Hydrogen Evolution Reaction.

Robust electrocatalysts toward the resourceful and sustainable generation of hydrogen by splitting of water via electrocatalytic hydrogen evolution reaction (HER) are a prerequisite to realize high-efficiency energy research. Highly electroactive catalysts for hydrogen production with ultralow loading of platinum (Pt) have been under exhaustive exploration to make them cutting-edge and cost-effectively reasonable for water splitting. Herein, we report the synthesis of hierarchically structured nickel pyrophosphate (β-Ni2P2O7) by a precipitation method and nickel phosphate (Ni3(PO4)2) by two different synthetic routes, namely, simple cost-effective precipitation and solution combustion processes. Thereafter, Pt-decorated nickel pyrophosphate and nickel phosphate (β-Ni2P2O7/Pt and Ni3(PO4)2/Pt) were prepared by using potassium hexachloroplatinate and ascorbic acid. The fabricated novel nickel pyrophosphate and nickel phosphate/Pt materials were utilized as potential and affordable electrocatalysts for HER by water splitting. The detailed electrochemical studies revealed that the β-Ni2P2O7/Pt (1 μg·cm-2 Pt) electrocatalyst showed excellent electrocatalytic performances for HER in acidic solution with an overpotential of 28 mV at -10 mA·cm-2, a Tafel slope of 32 mV·dec, and an exchange current density ( j0) of -1.31 mA·cm-2, which were close to the values obtained using the Vulcan/Pt (8.0 μg·cm-2 Pt), commercial benchmarking electrocatalyst with eight times higher Pt amount. Furthermore, the β-Ni2P2O7/Pt electrocatalyst maintains an excellent stability for over -0.1 V versus RHE for 12 days, keeping j0 equal after the stability test (-1.28 mA cm-2). Very well-distributed Pt NPs inside the "cages" on the β-Ni2P2O7 structure with a crystalline pattern of 0.67 nm distance to the Ni2P2O7/Pt electrocatalyst, helping the Volmer-Tafel mechanism with the Tafel reaction as a major rate-limiting step, help to liberate very fast the Pt sites after HER. The high electrocatalytic performance and remarkable durability showed the β-Ni2P2O7/Pt material to be a promising cost-effective electrocatalyst for hydrogen production.

Metal-organic frameworks derived bundled N-doped carbon nanowires confined cobalt phosphide nanocrystals as a robust electrocatalyst for hydrogen production

Exploring highly active, low-cost and further durable catalysts toward electrocatalytic hydrogen evolution reaction (HER) has become a research hotspot for investigators. VIII group transition metal phosphides (TMPs) gradually stand out due to their intriguing properties including low resistance, excellent catalytic activity and stability. Herein, we adopt an unconventional metal-organic framework (MOF) as precursor as well as an optimized pyrolytic strategy to fabricate a unique hybrid of bundled N-doped carbon nanowires confined small-sized cobalt phosphide (CoP) nanocrystals (CoP/NCNWs). As a HER catalyst, CoP/NCNWs hybrid exhibits excellent electrocatalytic activity with low overpotential and durable long-term stability in both acidic and alkaline solutions, respectively, which could be ascribed to the structural integrity of the hybrid and the synergetic effects between catalytically active CoP components and the protective N-doped carbon matrixes. Furthermore, the as-synthesized nanocomposite also presents favorable performances toward oxygen evolution reaction (OER). This research provides an operable strategy to construct low-dimensional carbonaceous materials coupled with TMPs using MOFs as precursor and shows the promising potential of multifunctional nanomaterials in electrocatalytic applications.

One-Dimensional Porous Hybrid Structure of Mo2C-CoP Encapsulated in N-Doped Carbon Derived from MOF: An Efficient Electrocatalyst for Hydrogen Evolution Reaction over the Entire pH Range.

The development of outstanding noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) has attracted broad interest. Herein, a novel one-dimensional (1D) HER hybrid catalyst consisted of cobalt phosphide (CoP) and molybdenum carbide (Mo2C) nanoparticles wrapped by nitrogen-doped graphitic carbon (called CoP/Mo2C-NC) was successfully fabricated by a facile continuous-flow method and a simple two-step annealing process. During these processes, the successful synthesis of the MoO3 nanorods coated with cobalt zeolitic imidazolate frameworks (Co-ZIF-67) (Co-ZIF-67@MoO3) through the continuous-flow method plays a key role. The as-synthesized CoP/Mo2C-NC hybrid electrocatalyst exhibits a significantly enhanced HER electrocatalytic activity over the entire pH range relative to that of the control materials CoP, Mo2C-NC, and physically mixed CoP and Mo2C-NC. The outstanding HER catalytic performance is mainly due to the fact that the electron cloud transfers from Co to Mo in CoP/Mo2C-NC through the Co-P-Mo bond, resulting in the formation of a high valence state for Co (Co3+) species and lower valence states for Mo (i.e., Mo2+, Mo3+) species, providing the abundant HER active sites. Moreover, the Gibbs free energy (Δ GH*) of CoP/Mo2C-NC obtained by the density function theory calculations indicates a good balance between the Volmer and Heyrovsky/Tafel steps in HER kinetics. Such a cobalt zeolitic imidazolate framework-mediated strategy depicted in this work offers an interesting perspective for developing highly efficient noble-metal-free electrocatalysts for hydrogen production.

High intrinsic catalytic activity of boron nanotubes for hydrogen evolution reaction: an ab initio study

Exploring efficient electro-catalysts for hydrogen production with earth-rich and non-noble elements is a promising pathway for electrochemical splitting of water. Boron (B) is the fifth element in the periodic table and the complexity of boron coordination number leads to the diversity of boron structure, which has great potential for the development of novel light material for hydrogen evolution reaction (HER). In this work, the electronic properties, catalytic performance and structural stability of boron nanotubes (BNTs) have been investigated using density functional theory. The calculation results show that the metallicity of BNTs is independent on their chirality and diameters but a strong diameter-dependent catalytic behavior is observed. The BNTs behave potentially high catalytic active for HER with a nearly zero free energy of hydrogen adsorption is presented when their diameters are larger than 11.5 and 13.0 Å for zigzag and armchair BNTs, respectively. This high catalytic performance is mainly due to the presence of a plenty of active sites on intrinsic nanotubes. This study opens a new way for the developing of non-metal tubular structures as candidates of catalyst for HER.

Two-Dimensional Sandwich-Structured Mesoporous Mo2C/Carbon/Graphene Nanohybrids for Efficient Hydrogen Production Electrocatalysts.

The main challenge in water electrolysis, an appealing technique to alleviate future energy crisis, is the design of efficient electrocatalysts for hydrogen evolution reaction (HER). On the basis of an interface self-assembly approach, we synthesize mesoporous nitrogen-doped carbon/Mo2C/reduced graphene oxide nanohybrids (denoted as mNC-Mo2C@rGO), which represent a new type of two-dimensional Mo2C/carbon hybrid nanomaterials and possess a sandwichlike structure with well-defined mesopores. The method involves the co-self-assembly of spherical micelles formed from polystyrene- block-poly(ethylene oxide), pyrrole (Py) monomers, and molybdate ions (Mo7O246-) on GO surfaces in aqueous solution, followed by polymerization of Py and calcination of the nanocomposites at 900 °C under nitrogen atmosphere. The resultant mNC-Mo2C@rGO nanosheets possess high N contents, large specific surface areas (SSAs), and 4 nm Mo2C particles well-distributed in the mesoporous carbon matrix. The Mo2C content is controllable in the range of 18.4-42.4 wt % by adjusting the feed amount of Mo7O246-. In particular, mNC-Mo2C@rGO with an SSA of 344 m2/g and a Mo2C content of ca. 28 wt % exhibits the highest HER catalytic activity in 1 M KOH electrolyte, with a 95 mV overpotential at 10 mA/cm2, a Tafel slope of 49.8 mV/dec, and a long-term stability of 60 h at 20 mA/cm2. This study blazes a trail for the synthesis of new functional nanomaterials with potential applications as efficient HER electrocatalysts.

Hierarchical Mo2C/C Scaffolds Organized by Nanosheets as Highly Efficient Electrocatalysts for Hydrogen Production

A facile and low-cost strategy is developed for the in situ synthesis of well-defined 3D porous scaffold-like Mo2C/C nanosheet hybrids as electrocatalysts for the hydrogen evolution reaction (HER). In this strategy, cubic NaCl particles play a critical template role in not only directing the formation of a 3D porous scaffold-like architecture but also creating a 2D-finite space to obtain Mo2C/C nanosheet hybrids. More importantly, the presence of NaCl will increase the content of amorphous carbon residue, reducing the charge transfer resistance. As a result, in this unique structure, the 3D porous scaffold can effectively avoid aggregation and expose more active sites, facilitating mass transportation, while the sheet-like Mo2C/C hybrids can achieve a relatively high density of catalytic sites with excellent charge transfer ability. Moreover, the effects of the mass ratio on the HER activity were also investigated. And the final optimized Mo2C/C electrocatalyst manifests an outstanding HER performance in ...

Mesoporous Mo2C/Carbon Hybrid Nanotubes Synthesized by a Dual-Template Self-Assembly Approach for an Efficient Hydrogen Production Electrocatalyst.

Molybdenum carbide-containing nanomaterials have drawn considerable attention in the application of hydrogen production electrocatalysts in light of the high abundance, low cost, and Pt-like electronic structure of molybdenum carbide. In this article, we report the synthesis of one-dimensional (1D) Mo2C/carbon mesoporous nanotubes (Mo2C/C PNTs) through a dual-template self-assembly approach, which employs 1D MoO3 nanobelts as the structure-directing template as well as one of the Mo2C precursors, along with block copolymer (BCP) micelles as the pore-forming template. In aqueous solution, the interface self-assembly of the micelles with pyrrole (Py) molecules absorbed in the PEO domains leads to the tight arrangement of the micelles on the surfaces of the MoO3 nanobelts. The polymerization of Py and the subsequent pyrolysis at 800 °C under a nitrogen atmosphere yield Mo2C/C PNTs with well-defined mesopores. Among the resultant Mo2C/C PNT samples, Mo2C/C PNTs with a specific surface area of 69 m2/g, a N atom percentage of 5.5 atom %, and an optimum Mo2C content of 40 wt % exhibit the highest HER catalytic performance in 0.5 M H2SO4 electrolyte, with a low onset potential of 34 mV, a satisfied overpotential of 140 mV at 10 mA/cm2, and excellent cycling stability. This study not only opens an avenue toward new Mo2C-containing nanomaterials but also provides a new system for the fundamental study on 1D porous nanohybrids with potential applications as hydrogen production electrocatalysts.

Crystalline Ru0.33Se Nanoparticles‐Decorated TiO2 Nanotube Arrays for Enhanced Hydrogen Evolution Reaction

Nowadays, the state-of-the-art electrocatalysts for hydrogen evolution reaction (HER) are platinum group metals. Nonetheless, Pt-based catalysts show decreased HER activity in alkaline media compared with that in acidic media due to the sluggish dissociation process of H2 O on the surface of Pt. With a cost 1/25 that of Pt, Ru demonstrates a favorable dissociation kinetics of absorbed H2 O. Herein, crystalline Ru0.33 Se nanoparticles are decorated onto TiO2 nanotube arrays (TNAs) to fabricate Ru0.33 Se @ TNA hybrid for HER. Owing to the large-specific surface area, Ru0.33 Se nanoparticles are freely distributed and the particle aggregation is eliminated, providing more active sites. The contracted electron transport pathway rendered by TiO2 nanotubes and the synergistic effect at the interface significantly improve the charge transfer efficiency in the hybrid catalyst. Compared with Ru0.33 Se nanoparticles deposited directly on the Ti foil (Ru0.33 Se/Ti) or carbon cloth (Ru0.33 Se/CC), Ru0.33 Se @ TNA shows an enhanced catalytic activity with an overpotential of 57 mV to afford a current density of 10 mA cm-2 , a Tafel slope of 50.0 mV dec-1 . Furthermore, the hybrid catalyst also exhibits an outstanding catalytic stability. The strategy here opens up a new synthetic avenue to the design of highly efficient hybrid electrocatalysts for hydrogen production.

Reduced Graphene Oxide-Supported Bimetallic M-Platinum (M: Co, Ni, Cu) Alloy Nanoparticles for Hydrogen Evolution Reaction

Hydrogen is one of the most promising energy carriers, especially if produced from renewable energy sources, replacing fossil fuels for both portable and stationary applications [1]. Although hydrogen is one of the most abundant elements on Earth, it does not exist in nature in molecular form. Currently, most of the hydrogen is produced from fossil fuel-based technologies, such as gas reforming. Only 5% of worldwide hydrogen production comes from water electrolysis. The main problem of this process is the high overpotentials necessary to split the water molecule into hydrogen and oxygen and, consequently, the high energy consumption. To overcome this problem, different electrode materials such as Pt, Ni, Co, Ir and Rh, have been tested as cathodes for water electrolyzers. Pt has high activity and good stability for the hydrogen evolution reaction (HER), but its limited resources and high price prevent its use on industrial scale [2]. Alkaline water electrolysis is a mature technology that typically operates at temperatures around 60 – 80 ºC and uses cathodes based on Ni, Raney Ni and Co [3]. These cathodes are less expensive than Pt, but show good activity (in alkaline media) and corrosion resistance. A common approach used in electrocatalysis to minimize the utilization of precious metals involves employing an electrocatalyst support material. The support material has several functions, as to increase the catalytic electrochemically surface area, to stabilize and to accommodate the metal particles and also to increase the catalyst’s conductivity [4-6]. Carbon-based supports are the mostly used, as they can offer all the aforementioned properties [6]. The present work combines the advantages of using highly active Pt together with low cost transition metals, like Ni, Co and Cu, with the employment of reduced graphene oxide (rGO) as an efficient carbon-based electrocatalyst support. Thus, Pt and three different PtM alloys supported on rGO, i.e., Pt/rGO, PtCo/rGO, PtCu/rGO and PtNi/rGO, were tested as electrocatalysts for hydrogen production by alkaline water electrolysis. rGO has adequate features to enhance and stabilize the metal particles, with rGO-supported catalysts having recently demonstrated promising results in alkaline media [7]. To prepare the working electrodes, 5 mg of each of the fours electrocatalysts was dispersed in 125 µL of 5 wt.% solution of polyvinylidene fluoride (PVDF, Alfa Aesar) in N-methyl-2-pyrrolidone (NMP, Sigma Aldrich) followed by ultrasonic treatment for ca. 30 min. The working electrodes were prepared by pipetting 80 μL of the corresponding catalytic ink onto a polished glassy carbon (GC) electrode (A = 4 cm2). The electrodes were dried at 80 ºC for 4 hours. A conventional three-electrode setup was used for the electrochemical characterization. The rGO-supported PtM (M = Co, Cu, Ni) electrode was used as working electrode, the counter electrode was a Pt mesh (Johnson Matthey) of 25 cm2 area, and a calomel electrode (Hanna Instruments, HI-5412, 3.5 M KCl) was used as the reference. All recorded potentials were converted to RHE scale using the equation ERHE = Ecal + 0.250 + 0.059 pH. The evaluation of HER kinetics at the PtM/rGO composites was done by linear scan voltammetry measurements at scan rate of 1 mV s-1, starting from the open circuit potential up to -0.17 V in 8 M KOH (AnalaR NORMAPUR, 87 wt.%) solutions. Higher current densities were achieved for the PtM/rGO electrocatalysts, in comparison with the non-alloyed material (Pt/rGO). It was also observed that increasing the temperature up to 65 ºC leads to a substantial increase of HER current densities at all electrocatalysts. Furthermore, long-term stability of the four electrocatalysts’ activity for HER was evaluated by chronoamperometry studies at 25 and 65 ºC, revealing better stability at lower temperature. It is shown that PtM/rGO nanocomposites are good candidates for application as novel electrocatalysts for the HER in alkaline media. [1] J.A.S.B. Cardoso, B. Šljukić, M. Erdem, C.A.C. Sequeira, D.M.F. Santos, Catalysts 50, 8 (2018). [2] D.M.F. Santos, B. Šljukić, C.A.C. Sequeira, D. Macciò, A. Saccone, J.L. Figueiredo, Energy 50, 486 (2013). [3] D.S.P. Cardoso, L. Amaral, D.M.F. Santos, B. Šljukić, C.A.C. Sequeira, D. Macciò, A. Saccone, Int. J. Hydrogen Energy 40, 4295 (2015). [4] M. Martins, B. Šljukić, C.A.C. Sequeira, O. Metin, M. Erdem, T. Şener, D.M.F. Santos, Int. J. Hydrogen Energy 41, 10914 (2016). [5] R.C.P. Oliveira, V. Vasić, D.M.F. Santos, B. Babić, R. Hercigonja, C.A.C. Sequeira, B. Šljukić, Electrochim. Acta 269, 517 (2018). [6] E. Antolini, Appl. Catal. B 88, 1 (2009). [7] M. Martins, B. Šljukić, O. Metin, M. Sevim, C.A.C. Sequeira, T. Şener, D.M.F. Santos, J. Alloys Compd. 718, 204 (2017).

Water Splitting Electrodes Based on Nife Alloy Foil Produced By Roll-to-Roll Processing

With the rapid increase of global temperature and depletion of fossil fuels, developing sustainable energy resources is crucial nowadays. Among the various renewable energy source generation approaches, water splitting has attracted increasing attention for clean energy generation and efficient energy storage. Electrochemical production of hydrogen from solar electricity is also an attractive option for generating energy in the form of a hydrogen which could be used at a later stage for electricity. Over the past decades, despite of significant achievements have been obtained, the solar-to-hydrogen (STH) efficiency is still too low for practical applications. Low solar to hydrogen (STH) conversion efficiency is due to the suppressed water splitting reactions by high overpotential, especially oxygen evolution reaction. Due to relatively high overpotential than hydrogen evolution reaction(HER), the oxygen evolution reaction(OER) is a key reaction in water splitting. To overcome this problem, current studies are focused on development of efficient, abundant and inexpensive OER catalyst. The implementation of efficient electrocatalyst leads to decreased overpotentials, thereby making the whole process more energy-efficiently. Currently, the most efficient catalysts for water splitting are noble-metal catalysts such as Pt-group metals, Ru and Ir-based compounds. Unfortunately, the scarcity and high cost of noble metals seriously impede its large-scale applications in electrocatalytic water splitting. It is therefore highly attractive to explore earth-abundant materials to overcome this obstacle. In past decades, Ni has emerged as an important non-noble metal due to its catalytic power for water splitting and Ni-based compounds have been intensively studied as efficient OER and HER catalysts. Among the various type of Ni based materials, layered transition-metal alloy with Fe have attracted much attention of researchers because of their special redox character and good accessibility for the reaction species. Bimetallic electrocatalysts also have attracted increasing attention as a reliable approach to enhanced electrocatalytic activity for the HER. In the meantime, inspired by the abundant element Ni used in nature, various Ni-based catalysts have been designed to catalyze the conversion of H2O to H2 in commercial alkaline electrolyzers. Among these, Ni–Mo alloys are well-known non-precious-metal electrocatalysts for hydrogen production in alkaline electrolytes because of the increased intrinsic electrocatalytic caused by appropriate binding energy to hydrogen activity compared to pure Ni.Herein we report an approach to improve efficiency of water splitting electrodes based on flexible NiFe-based foil. Anodic oxidation method is applied to enhance the oxygen evolution activity of NiFe alloy foil. The anodized NiFe alloy foil exhibit significant higher activity than the corresponding Ni foam in base conditions. The anodic oxidation method generate NiFe oxide and hydroxide layers on NiFe alloy surface, act as electrocatalyst. Spontaneously, the anodic oxidation method widen the specific surface area of water splitting electrodes. Increased reaction sites and catalytic behavior of NiFe hydroxide is the reason of improved water splitting property. Because Ni based alloy like NiMo is remarkable hydrogen evolution catalyst, similar to noble metal, electrodeposition method is applied to enhance the hydrogen evolution activity of NiFe alloy foil. NiMo electrodeposited NiFe alloy foil exhibit highly enhanced activity than pure NiFe foil. Combining with 23% Si based solar cell using anodized NiFe alloy foil as anode and electrodeposited NiMo as cathode, PV-EC cell shows excellent STH properties around 18%.