Hydrogen evolution stability of platinum modified graphite electrode

A Platinum-modified alloy coating with high hydrogen evolution reaction (HER) durability activity was prepared by electrodeposition. The durability of this catalyst was determined with electrolysis technique for 120 h. The prepared electrode was characterized by energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Long-term electrolysis was carried out in 1 M KOH solution by cathodic current–potential curves and electrochemical impedance spectroscopy (EIS). Experimental result showed that CoZn–Pt coating has a rough structure and presents good stability and high durability. Electrochemical activity increases slightly with increasing electrolysis time. High durability of Pt modified cathode was attributed to the high surface area and synergistic interaction between Co, Zn and Pt.     

Ni-W nanostructure well-marked by Ni selective etching for enhanced hydrogen evolution reaction

Designing active, stable and affordable electrocatalysts is a promising pathway for fulfilling the mankind's dream of preserving unsustainable fuel sources. Herein, the facile utilization of Romanesco-like and arrow-like nanostructures of Ni-W samples is introduced. Exclusive emphasis is placed on achievement of the unique nanostructure through cost-effective, repeatable and readily accessible two-step techniques, i.e. Ni-W electrodeposition approach followed by etching treatment. Microscopic study was fully utilized for surface morphology and structural investigation. The electrochemical analysis was used to evaluate the electrocatalytic activity and stability. The surface roughness of the Ni-W film electrodeposited by D.C = 90% and etched via acidic solution was up to 93.85, considerably higher than that of the Ni-W electrodeposited by D.C = 20% and without etched Ni-W films (55.36 and 41.51 respectively). Therefore, HER activity was improved with η₁₀ and η₂₀ of 169 and 226 mV vs. RHE, respectively, due to higher effective active surface for H⁺ adsorption. The Tafel slope analysis suggests Volmer mechanism as the HER rate-determining step. The electrochemically active surface area was also enhanced from roughly 2 to 10 cm². In addition, wettability was investigated by a contact angle of less than 65°, which indicates high penetration of electrolyte to the nanostructure. Rapid separation of bubbles on the arrow-like nanostructure of Ni-W films exhibited unstable H₂ bubbles on surface of the electrode.     

Fabrication of highly porous Pt coated nanostructured Cu-foam modified copper electrode and its enhanced catalytic ability for hydrogen evolution reaction

The nanoporous copper foam was prepared by electrochemical reduction of copper ion at the copper substrate. The as-prepared substrate was used as three-dimensional templates for preparation of Pt coated nanostructured Cu-foam by galvanic replacement of Cu with platinum by simply immersing the prepared nanoporous copper foam in a K₂PtCl₆ aqueous solution. The structure and nature of the fabricated Pt coated nanostructured Cu-foam was characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Pt coated nanostructured Cu-foam modified copper electrode exhibited remarkable electrocatalytic activity for the hydrogen evolution reaction. The effect of electrodeposition time during Cu-foam formation on the kinetic constants for hydrogen evolution reaction was comparatively investigated.     

Tunably fabricated nanotremella-like Bi2S3/MoS2: An excellent and highly stable electrocatalyst for alkaline hydrogen evolution reaction

Reasonable design of efficient and stable catalysts with low cost and abundant natural reserves is vital for electrocatalytic water splitting. Herein, novel nanotremella-like Bi₂S₃/MoS₂ composites with different mass ratios between Bi₂S₃ and MoS₂ have been successfully prepared through a hydrothermal approach and further applied to hydrogen evolution reaction (HER) in 1.0 M KOH electrolyte for the first time. When the mass ratio of Bi₂S₃ and MoS₂ is 5:5, as-prepared nanotremella-like Bi₂S₃/MoS₂ (marked as BMS-5) manifests favorable HER catalytic activity with overpotential of 124 mV at current density of 10 mA cm⁻² and relatively low Tafel slope of 123 mV dec⁻¹. Moreover, it exhibits an extraordinary durability for uninterrupted hydrogen generation. The enhanced HER performances are ascribed to the synergistic effects between Bi₂S₃ and MoS₂, giving rise to large electrocatalytic active area and fast HER kinetics. The results pave a new path to design and construct excellent Bi₂S₃/MoS₂ nanomaterials for electrocatalytic hydrogen generation.     

Defective-MoS2/rGO heterostructures with conductive 1T phase MoS2 for efficient hydrogen evolution reaction

As a two-dimensional material, molybdenum disulfide (MoS₂) exhibits great potential to replace metal platinum-based catalysts for hydrogen evolution reaction (HER). However, poor electrical conductivity and low intrinsic activity of MoS₂ limit its application in electrocatalysis. Herein, we prepare a defective-MoS₂/rGO heterostructures material containing 1T phase MoS₂ and evaluate its HER performance. The experimental results shown that defective-MoS₂/rGO heterostructures exhibits outstanding HER performance with a low overpotential at 154.77 mV affording the current density of 10 mA cm^?2 and small Tafel slope of 56.17 mV dec^?1. The unique HER performance of as-prepared catalyst can be attributed to the presence of 1T phase MoS₂, which has more active sites and higher intrinsic conductivity. While the defects of as-prepared catalyst fully expose the active sites and further improve catalytic activity. Furthermore, the interaction between MoS₂ and rGO heterostructures can accelerate electron transfer kinetics, and effectively ensure that the obtained catalyst displays excellent conductivity and structural stability, so the as-prepared catalyst also exhibits outstanding electrochemical cycling stability. This work provides a feasible and effective method for preparation of defective-MoS₂/rGO heterostructures, which also supplies a new strategy for designing of highly active and conductive catalysts for HER.     

Tungsten-molybdenum oxide nanowires/reduced graphene oxide nanocomposite with enhanced and durable performance for electrocatalytic hydrogen evolution reaction

Hydrogen has attracted huge interest globally as a durable, environmentally safe and renewable fuel. Electrocatalytic hydrogen evolution reaction (HER) is one of the most promising methods for large scale hydrogen production, but the high cost of Pt-based materials which exhibit the highest activity for HER forced researchers to find alternative electro-catalyst. In this study, we report noble metal free a 3D hybrid composite of tungsten-molybdenum oxide and reduced graphene oxide (GO) prepared by a simple one step hydrothermal method for HER. Benefitting from the synergistic effect between tungsten-molybdenum oxide nanowires and reduced graphene oxide, the obtained W-Mo-O/rGO nanocomposite showed excellent electro-catalytic activity for HER with onset potential 50 mV, a Tafel slope of 46 mV decade^?1 and a large cathodic current, while the tungsten-molybdenum oxide nanowires itself is not as efficient HER catalyst. Additionally, W-Mo-O/rGO composite also demonstrated good durability up to 2000 cycles in acidic medium. The enhanced and durable hydrogen evolution reaction activity stemmed from the synergistic effect broadens noble metal free catalysts for HER and provides an insight into the design and synthesis of low-cost and environment friendly catalysts in electrochemical hydrogen production.     

Synergistic coupling of CoFe-layered double hydroxide nanosheet arrays with reduced graphene oxide modified Ni foam for highly efficient oxygen evolution reaction and hydrogen evolution reaction

Novel CoFe-LDH (layered double hydroxide) nanosheet arrays in situ grown on rGO (reduced graphene oxide) uniformly modified Ni foam were synthesized by a citric acid-assisted aqueous phase coprecipitation strategy. Systematic characterizations indicates that the series of Co_xFe₁-LDH/rGO/NF (x = 4, 3, 2) all show Co_xFe₁-LDH nanosheets (150–180 × 15 nm) grown vertically on the surface of rGO/NF. Especially, the Co₃Fe₁-LDH/rGO/NF exhibits the best performance with overpotentials of 250 and 110 mV at 10 mA cm^?2 in 1 M KOH for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. When it is used as cathode and anode simultaneously for overall water splitting, they require 1.65 and 1.84 V at 10 and 100 mA cm^?2, respectively. Excellent performance of Co₃Fe₁-LDH/rGO/NF is due to the nanosheet arrays structure with open channels, synergistic coupling between Co₃Fe₁-LDH and rGO enhancing electrical conductivity, and in-situ growth of Co₃Fe₁-LDH on rGO/NF enhancing stability.     

Exfoliated MoS2 with porous graphene nanosheets for enhanced electrochemical hydrogen evolution

Porous graphene (P-rGO) was synthesized from graphene oxide (GO) via a one-pot calcination method with CO₂ as an activation agent at 800 °C. Due to the special porous structure, the surface area of P-rGO can be increased to ～759 m²/g. The P-rGO was then used as a support to incorporate with chemical exfoliated molybdenum disulfide (MoS₂) for the fabrication of MoS₂/P-rGO composite. Compared to bulk MoS₂, the exfoliated MoS₂ is in the 1T phase with a metallic property and smaller charge transfer resistance, thus has a better activity in electrochemical hydrogen evolution reaction (HER). The HER activity of 1T MoS₂ could be further increased after the combination with P-rGO. The overpotential of 1T MoS₂/P-rGO was only ～130 mV vs. RHE, and the corresponding Tafel slope was ～75 mV Dec^?1. The special porous structure and good electric conductivity of P-rGO decrease the charge transfer resistance of the composite without sheltering too many active sites of MoS₂, thus leading to the enhanced HER activity. As an efficient noble metal free HER catalyst, the 1T MoS₂/P-rGO has great potential for large-scale hydrogen production.     

A facile one-pot synthesis of microspherical-shaped CoS2/CNT composite as Pt-free electrocatalyst for efficient hydrogen evolution reaction

Hydrogen evolution reaction has been recognized as a green technology in the field of electrochemical energy conversion and storage devices. Nevertheless, it is necessary task to finding an economical and effective electrocatalysts for HER. Among the different HER catalysts, the cobalt disulfide (CoS₂) showed an excellent HER activity owing to its low cost, easy to synthesize and good stability. Hence, in this work, we prepared a series of CoS₂/CNT composites with different contents CNT from 4 to 12 wt% by a simple one-step hydrothermal method to investigate the influence of CNT on HER activity of CoS₂. The structural and morphological properties of the obtained samples were analyzed through XRD, SEM, HR-TEM, and XPS. The SEM images of CoS₂/CNT composite showed the spherical-shaped CoS₂ covered by the CNT nanostructure. In addition, the electrochemical tests were carried out using 0.5 M H₂SO₄ solution in order to assess their HER activity. The attained electrochemical results showed that the CoS₂/CNT composite with 8% CNT offers an outstanding HER activity with the smallest overpotential of 155 mV at 10 mA cm⁻² and lowest Tafel slope of 59 mV dec⁻¹ when compared with other composites. Also, the optimized CoS₂/CNT composite provided excellent stability in the acidic medium after 1000 cycles. Therefore, the as-synthesized CoS₂/CNT composite will be an efficient, low-cost and Pt-free electrocatalyst for HER application.     

Hydrogen deactivation of sputter-deposited platinum thin films on highly oriented pyrolytic graphite

Electrochemical techniques such as chronopotentiometry and a.c. impedance spectroscopy have been used successfully to characterise the behavior of sputter-deposited platinum on highly oriented pyrolytic graphite (HOPG) substrate under hydrogen evolution reaction (HER) in 1 M NaOH at 25 °C. Prior to the sputtering process, HOPG surfaces were etched up to 60 min and deposition time was varied up to 20 min. Under a constant applied current density, the rate of overpotential increase with time and its magnitude are strongly related to the experimental conditions during the electrode preparation. Deactivation during HER is attributed to a loss of sputtered platinum due to its poor adhesion to the substrate.     

Nickel-based nanosheets array as a binder free and highly efficient catalyst for electrochemical hydrogen evolution reaction

Hydrogen technology through water electrolyzer systems has attracted a great attention to overcome the energy crisis. So, rationally designed non-noble metal based-electrocatalysts with high activity and durability can lead to high performance water electrolyzer systems and high purity hydrogen generation. Herein, a facile two-step method: hydrothermal and electrodeposition, respectively, are developed to decorate highly porous three-dimensional binder-free structure NiFeO/NiO nanosheets array on Ni foam (NiFeO/NiO/NF) with robust adhesion as a high-performance electrode for Hydrogen Evolution Reaction (HER).The electrodeposition process applied after the initial hydrothermal process provides a stable structure and, in addition, enhances the sluggish hydrogen evolution efficiency. In alkaline media, the developed electrode needs an overpotential of 48 and 188 mV to drive current densities (j) of 10 and 100 mA cm^?2, respectively. After continuous 110 h electrochemical stability test under j = 150 mA cm^?2 conditions, demonstrates an excellent stability with ignorable activity decrease. Such superior HER catalytic performance can be derived from the synergistic effect between Ni and Fe atoms, also exposure to a high number of active sites on the nanosheets, and good dynamic with effective electron transport along the nanosheets. The present work provides a promising route for the design and fabrication of cost-effective and highly efficient HER electrocatalysts.     

Quaternary-metal phosphide as electrocatalyst for efficient hydrogen evolution reaction in alkaline solution

Hydrogen evolution reaction (HER) is a critical process in electrocatalytic water splitting for hydrogen production. However, the development of low-cost electrocatalysts for highly efficient HER is still a huge challenge. Hence, we fabricate a multi-metal phosphide on Ni foam, FeCoNiNb_xP, through a facile hydrothermal reaction followed by phosphorization. We find that Nb promotes the formation of metal phosphides, and the main phases of the catalysts with Nb are multiphase phosphides. Importantly, the Nb incorporation significantly improves the HER activity of FeCoNiP. We show that FeCoNiNb_0.3P has the best HER activity, which only requires an overpotential of 78 mV to achieve a current density of 10 mA cm^?2 in 1 M KOH, and demonstrates excellent stability under both constant potential and varied current densities. Our findings show that the multiple-metal compounds are beneficial to the improvement of catalytic activity and provide guidance on the design of novel catalysts for applications.     

Cobalt-molybdenum disulfide supported on nitrogen-doped graphene towards an efficient hydrogen evolution reaction

Herein, the cobalt-molybdenum bimetallic sulfide catalysts supported on nitrogen-doped graphene (CoMoS₂/NGO) were facilely synthesized by a one-pot hydrothermal route. These composites exhibit various special nanostructures, rich in abundant edge site exposure and defects, which play an important role in providing active sites for catalyzing hydrogen evolution reaction (HER). When hydrogen peroxide (H₂O₂) was used as an additive in hydrothermal process, the as-fabricated composite exhibited more efficiency towards HER, showing as low onset overpotential (η_on) as −54 mV in 0.5 M H₂SO₄. Typical H₂O₂-assisted composite realized a remarkable cathodic current density of 30 mA cm⁻² at an overpotential η = −137 mV and it possessed a small Tafel slope of 34.13 mV dec⁻¹. Moreover, it exhibited an excellent cycling stability and superior electronic exchange rate. The results prove that CoMoS₂/NGO catalysts have great potential for electrochemical HER.     

Nanostructure and stoichiometry tailoring of CoS2 for high performance hydrogen evolution reaction

Developing efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) is important for hydrogen fuel production. In this study, we synthesized two different types of CoS₂ under low sulfur (LS) and high sulfur concentration (HS) conditions. Structural analysis results show that CoS impurity phase forms easily when the concentration of sulfur is low, while at high sulfur concentration the growth of CoS impurity phase is inhibited and leads to phase-pure CoS₂. Electrochemical investigation of HER performance reveals that the onset potential of CoS₂ (HS) electrode (ca. − 0.11 V vs. the reversible hydrogen electrode, RHE) is 30 mV anodic of the CoS₂ (LS) one (ca. − 0.14 V vs. RHE). At a specific current density of 10 mA cm⁻² the required overpotential on CoS₂ (HS) electrode is only 163 mV, which is 40 mV less than the CoS₂ (LS) electrode. Electrochemical impedance spectroscopy (EIS) data further demonstrate that the charge transfer rate of CoS₂ (HS) electrode is faster than that of CoS₂ (LS) electrode towards HER.     

Catalytic enhancement of hydrogen evolution reaction on copper in the presence of benzylamine

Benzylamine catalytic effect on the cathodic hydrogen evolution in acid aqueous solution has been studied on copper electrode. Experimental results obtained by voltammetric techniques emphasize that the presence of benzylamine in 1 M sulfuric acid solution enhances the hydrogen evolution reaction (HER). In such a solution, benzylamine is protonated and exists as benzylammonium cation. Kinetic parameters of HER have been determined, observing a significant increase of the exchange current in the presence of benzylamine. Also, a decrease of the cathodic transfer coefficient has been noticed. Activation energy for HER has been computed on the basis of the Arrhenius plots. In the presence of benzylamine the activation energy was 33.0 kJ mol⁻¹, whereas without benzylamine a greater value was obtained: 94.6 kJ mol⁻¹. The catalytic effect of benzylamine was confirmed by electrochemical impedance spectroscopy. The considerable diminution of the double layer capacity is a valid proof of the strong adsorption of benzylamine at the Cu - sulfuric acid solution interface, while the reduction of the charge transfer resistance is a symptom of the enhancement of HER. Ab initio molecular modeling of benzylammonium ion showed that, due to a high value of the dipole moment, the molecules are oriented in the most favorable position for the charge transfer reaction, i.e., with the protonated amino group facing toward the electrode.     

Nanocoral-like NiSe2 modified with CeO2: A highly active and durable electrocatalyst for hydrogen evolution in alkaline solution

The excessive exhaustion of conventional fossil fuels and increasingly severe environmental issues prompt us to grope for high-performance and cost-effective catalysts for hydrogen evolution reaction (HER) by electrocatalytic water splitting. In this work, nanocoral-like NiSe₂ catalysts modified with CeO₂ have been successfully prepared through one-pot hydrothermal route and utilized to electrocatalytic HER in alkaline solution. It turns out that nanocoral-like NiSe₂ (labeled as CNS-2) catalyst delivers current densities of 10 and 50 mA cm⁻² at overpotentials of only 130 and 242 mV, respectively. Additionally, CNS-2 takes on a small Tafel slope of 115 mV dec⁻¹ and low charge transfer resistance, revealing a quicker Faradaic process and more favorable HER kinetics. Furthermore, it displays considerable long-term stability during the constant hydrogen producing. The strategy of fabricating NiSe₂ modified with CeO₂ unfolds a novel angle of view for exploiting highly efficient and durable catalysts for electrocatalytic HER.     

High-temperature-treated multiwall carbon nanotubes for hydrogen evolution reaction

We investigated the hydrogen evolution reaction (HER) properties of multi-wall carbon nanotubes (MWCNTs) treated at extremely high temperature (2600 °C). The heat treatment not only improves the crystallinity of the MWCNTs, but also reduces the carbon-oxygen (CO) bonding as it is replaced by the defect-carbon (sp³ and CH) bonding. These modifications in the heat treated MWCNT structure lead to the increase of electrochemical charge transfer. The heat treatment of MWCNTs in the composite with Pt (MWCNT-Pt composite) further facilitates electrocatalysis. The MWCNTs-Pt composite shows strong enhancement in the HER performance with an onset of overpotential of ?0.04 V vs reversible hydrogen electrode and a Tafel slope of 10.9 mV/decade. This performance is indeed better than that of Pt, which is the best working material for HER.     

Self-supported N-Doped Carbon@NiXCo2-XP core-shell nanorod arrays on 3D Ni foam for boosted hydrogen evolution reaction

The development of highly efficient and low-cost electrocatalysts for large-scale hydrogen evolution reaction (HER) is great important but remains a significant challenge. Transition-metal phosphides (TMPs) have attracted intense attention as promising non-noble-metal HER electrocatalysts due to their unique electronic properties and high intrinsic catalytic activities. Herein, we directly grew Ni_XCo_2-XP nanorod wrapped with N-doped carbon shell on 3D Ni foam to fabricate a self-supported electrode with core-shell nanorod array morphology. The obtained hybrid electrode exhibits remarkable electrocatalytic HER activity over a wide pH range with low overpotentials of 121 mV and 181 mV to obtain the current density of 200 mA cm⁻² in 0.5 M H₂SO₄ and 1 M KOH electrolytes, respectively, which is comparable to that of the current state-of-the-art Pt/C electrocatalyst. The experimental results indicate that the elaborate architectural superiority and compositional synergy of this hybrid electrode give rise to the boosted HER performance.     

Porous N-doped Mo2C@C nanoparticles for high-performance hydrogen evolution reaction

Exploration for an earth-rich and competent electrocatalyst for the hydrogen evolution reaction (HER) is a significant and challenging approach to confronting the resources shortage and environmental crisis. Porous N-doped Mo₂C@C (N-Mo₂C@C) nanoparticles self-encapsulated in nanospheres are presented as a high-performing HER electrocatalyst fabricated through a one-pot solvothermal method followed by hydrogen calcination. Structural analyses show that acetamide can regulate the size of the nanospheres, provide a N source for doping and form porous structures composed of Mo₂C, which suggests the exposure of extensive active sites as well as the contact and diffusion among the medium, electrodes, and gas. Theoretical calculations show that the N doping can enhance the activity of the Mo-C bond, reduce the energy of capturing hydrogen intermediates, and increase the catalytic conductivity. This work offers a simple and promising strategy to understand the catalytic mechanism required to optimize the activity of Mo-based electrocatalysts via N doping.     

Hydrogen evolution reaction in PTFE bonded Raney-Ni electrodes

This study is concerned with the hydrogen evolution reaction (HER) in several PTFE bonded Raney-Ni electrodes as function of temperature and treatments. The Mo-doped Raney-Ni catalysts are activated by hours of long cathodic polarization interleaved with few deep “charge - discharge” (polarity reversal) cycles. Moreover, the HER efficiency of the electrode requires additives which enhance conductivity and surface properties: with powders of Ni alloys (Ni-Ti, Ni-Cr, Ni-Fe) the electrode becomes also more stable, and almost insensitive to polarity reversal. The main effect of a temperature increase is the reduction of the Tafel slope, which is about 120 mV/dec at 25 °C, and about 60 mV/dec at 60 °C. A proper choice of additives yield electrodes which withstand polarity reversal and may be used in electrolysers which are intermittently operated, or have anodes which require periodic in situ re-activation by reduction.