Hydrogen Evolution In Alkaline Media Research Articles

Nickel oxide/nickel nanohybrids for oxygen and hydrogen evolution in alkaline media

Ni-based materials are cost-efficient electrocatalysts for the oxygen and hydrogen evolution reactions (OER and HER). Specifically, high-valence nickel oxides have been recently identified as highly active for both reactions; however, the origin of their activity during operation, particularly towards the HER, is still undefined. Herein, electrodeposition was used to produce Ni-based electrocatalysts supported on carbon fiber paper, followed by UV/O3 treatment to oxidize and modify their surface chemistry. The resulting electrodes were composed of nanoclusters formed by a metallic nickel core and ultrathin sheets of a high-valence nickel oxide whose crystalline structure was similar to NiO2, with Ni2+/Ni3+ oxidation states. Upon investigating the effect of the electrochemical conditioning of these high-valence nickel oxide/nickel electrodes, confirming the formation of surface β-Ni(OH)2. This surface layer improved the performance of the electrode by providing active sites for H2O adsorption and dissociation, as indicated by detailed density functional theory (DFT) calculations. The origin of the higher HER activity of β-Ni(OH)2 (001) surface compared to NiO2 (2D), and Ni (111) surfaces is attributed to its unique electronic structure. The high valence nickel oxide/nickel electrodes possessed robust long-term OER and HER stability over 24h Finally, the potential for modifying the structural composition of these electrodes and their use as bifunctional electrocatalysts for the water-splitting reaction was demonstrated by using the resulting electrodes in an electrolyzer coupled with/without a photovoltaic cell.

Surficial Reconstruction of Pt-Ni/NiS and Its Effect on Electrocatalytic Hydrogen Evolution in Alkaline Medium.

Cyclic voltammetry pretreatment of Pt-based electrocatalysts has been proven to be a normal activation process on achieving the optimal alkaline hydrogen evolution performance. Until now, the congruent relationship between the microstructural evolution and performance improvement during this process has rarely been reported. Herein, when the in situ transmission electron microscopy and in situ Raman analyses are employed, a self-reconstruction process from crystalline NiS into amorphous nickel hydroxide hydrate [Ni(OH)2-x·H2O, where x ≈ 0.3] on the surface of platinum-nickel nanowires has first been captured, which is the critical water dissociation active site to offer a sufficient proton supply. Furthermore, such a surficial reconstruction triggers an increase in the current density from -2.3 to -38.8 mA/cm2 (at -70 mV), which is nearly 17 times. These observations point to the fact that it is essential to consider the fundamental mechanisms of hydrogen evolution on the active sites when the process is scaled up.

On the Origins of Intrinsic Limitations of Electrocatalytic Hydrogen Evolution in Alkaline Media

AbstractElectrocatalytic hydrogen evolution reaction (HER) in alkaline media was investigated in comparative relationship to HER in acidic media. Experimentally obtained adsorption free energies for 13 d‐metals were used to study the impact of intermediate coverage on HER activity trends, and how activity trends relate to trends in activation energies and preexponential frequency factors. A mechanistic picture of water discharge and adsorbed intermediate formation was analyzed in the light of recent experimental findings with the goal of creating a more comprehensive picture of HER electrocatalysis in alkaline media.

In-situ growth of MoSe2 on N-doped Ti3C2Tx for electrocatalytic hydrogen evolution in alkaline media

Abstract Serious environmental contamination and the energy crisis have heightened public desire for new renewable energy sources. Because of its high energy content and non-polluting qualities, hydrogen energy has emerged as a viable alternative to fossil fuels. Currently, high-purity hydrogen is typically produced through water electrolysis. The sensible use of electrocatalysts in this process can significantly minimize power usage in the electrolysis of water, which is of great significance to industrial production. However, the electrocatalyst that is inexpensive, has abundant reserves and performs well has yet to be discovered, severely restricting the promotion and application of hydrogen energy. In this paper, a MoSe2/N-doped Ti3C2TX heterostructure with notable electrocatalytic hydrogen evolution activity in an alkaline environment was fabricated via nitrogen doping and in-situ growth of molybdenum selenide. When the current density is 10 mA·cm-2, its overpotential and Tafel slope are 321.87 mV and 139.97 mV·dec-1, respectively. This work serves as a valuable experimental reference for the development of non-noble metal electrocatalysts based on two-dimensional materials.

Cobalt phosphide embedded on interconnected ultrathin carbon nanosheets as an electrocatalyst for hydrogen evolution in alkaline medium

A highly effective hydrogen evolution reaction (HER) electrocatalyst was developed by combining Co2P nanoparticles (Co2P NPs) embedded on interconnected and ultrathin carbon nanosheets (CNS) through a facial in-situ thermal decomposition of the cobalt-triphenylphosphine complex. CNS were derived from the pyrolysis of sodium citrate in one step, resulting in an interconnected ultrathin nanosheet structure with a small thickness. The interaction between Co2P NPs and CNS boosted the electron transfer rate, resulting in a remarkable electrocatalytic performance toward the HER in an alkaline solution with excellent durability. An overpotential of −200 mV vs. RHE was sufficient to afford a current density of −10 mA cm−2 with a Tafel slope of 83.4 mV dec−1 in potassium hydroxide medium (1.0 M), which are lower than that of Co2P nanoparticles (-250 mV) with Tafel slope 93.3 mV dec−1. The electrochemical impedance spectroscopy data illustrated that the mutual coupling between the Co2P NPs and CNS supports the electrochemical HER performance and accelerates the kinetic of electron transfer. The high HER activity of the novel Co2P NPs/CNS catalyst is ascribed to the presence of CNS robust support.

Size engineering of porous CuWO4–CuO heterojunction for enhanced hydrogen evolution in alkaline media

Constructing electrocatalysts with heterogeneous interfaces is of great significance for improving the performance of electrocatalytic hydrogen production. In this work, CuWO4·2H2O–CuO (P-CWOC) was synthesized by hydrothermal method, and spherical porous CuWO4–CuO (CWOC) was obtained through annealing treatment. The size of CuWO4–CuO can be controlled from 72 to 221 nm by regulating the supersaturation of the solution. Among them, CuWO4–CuO with a particle size of 72 nm (CWOC-72) possesses the most oxygen vacancies and the largest specific surface area. The W atom in the heterostructure of CuWO4 and CuO can affect the electronic structure of Cu atoms, and the presence of oxygen vacancies is beneficial for increasing the surface oxygen affinity of the composite material. Benefitting from the largest number of oxygen vacancies and the largest specific surface area, the CWOC-72 own the best catalytic performance compared to the other four catalysts. The overpotential at a current density of 10 mA cm−2 is 121 mV, and the Tafel slope is 70 mV·dec−1. Its excellent stability was confirmed by chronoamperometry, in-situ XRD, and in-situ Raman spectroscopy, and its alkaline HER performance is superior to most CuO-based catalysts.

P-Ni co-doped Mo2C embedded in carbon-fiber paper as a highly efficient electrocatalyst for hydrogen evolution in alkaline media

The development of noble-metal-free electrocatalysts with high electrocatalytic performance and stability by adopting a scalable route is key to solving the energy crisis. We report a PNi co-doped Mo2C-based electrocatalyst with high hydrogen evolution reaction (HER) catalytic activity prepared by a molten-salt method. Using phosphating times of 2 h and 4 h yielded P-Ni-Mo2C-2h and P-Ni-Mo2C-4h, respectively, both of which exhibited nanoflower-like structures that provided abundant active sites for the reaction. P-Ni-Mo2C-2h possessed good electrocatalytic properties with a low overpotential of only 140.5 mV at j = 10 mA cm−2 and a small Tafel slope of 50.7 mV dec−1 in an alkaline environment. P-Ni-Mo2C-2h exhibited excellent stability after 20 h of continuous hydrogen production. The use of an excessively long phosphating time caused a narrow down of spaces formed by nanoflakes, thereby reducing the HER performance of the electrocatalyst. The results of this study provide guidelines for the preparation of high-efficiency PNi co-doped electrocatalysts.

Mass synthesis of Pt/C catalysts with high Pt loading for low-overpotential hydrogen evolution

We present a facile and scalable method to synthesize Pt/C catalysts with high Pt loading (10–30 wt.%) using sodium polyacrylate resin (PAANa) as a multifunctional agent. PAANa can absorb H2PtCl6 solution and form a gel, which can be converted into Pt/C catalysts by pyrolysis. PAANa acts as a water absorber, a Pt stabilizer, and a carbon precursor. The optimized catalyst, pyrolyzed at 800 °C with a 20 wt.% Pt loading, demonstrates Pt nanoparticles measuring 3.5 nm in size. It exhibits excellent stability and achieves a low overpotential of 43 mV at a current density of 10 mA cm−2 for the hydrogen evolution in alkaline media. The enhanced catalytic activity is due to the combined influence of the nanoscale Pt particles, the higher degree of graphitization, and the porous carbon substrate with a large surface area. We also demonstrate the scalability of the method by producing 100 g of the catalyst in the laboratory.

HF-free microwave-assisted synthesis of MXene as an electrocatalyst for hydrogen evolution in alkaline media.

MXenes, characterized by their robustness, flexibility, and large surface-to-volume ratio facilitating efficient energy transfer with fast response times, have emerged as promising electrocatalysts for hydrogen generation through electrochemical water-splitting. However, the conventional synthetic route to MXenes typically involves the use of hydrofluoric acid (HF) to obtain MXenes with terminal F-functional groups. Unfortunately, these fluorine groups can negatively impact the electrocatalytic performance of MXenes. Moreover, HF is highly toxic, necessitating the development of more environmentally friendly synthetic methods. In response to these challenges, we have developed a novel HF-free microwave-assisted synthesis approach for MXenes. This method harnesses the benefits of uniform heating, homogeneous nucleation, and rapid crystal development, resulting in MXene crystallites with limited size. Importantly, our microwave-assisted approach utilizes a fluoride-free, less hazardous etchant as compared to HF for the synthesis and functionalization of MXene. The as-obtained MXene exhibits significantly improved performance towards the electrochemical hydrogen evolution reaction in alkaline media. Specifically, it demonstrates an overpotential of 140 mV at a current density of 10 mA cm-2 and a Tafel slope of 84 mV dec-1. These results highlight the potential of our HF-free microwave-assisted synthesis approach for producing high-quality MXenes with enhanced electrocatalytic activity for hydrogen generation.

Nickel-based composites using tungsten carbides as enhancers for electroactivity for the hydrogen evolution reaction

This study explores the impact of incorporating tungsten carbides into a Watts bath on the fabrication of Ni/WC and Ni/W2C composites, comparing them with conventional Ni Watts electrodeposited electrodes. Results indicate that adding tungsten carbides to the conventional nickel bath forms rougher and more porous structures in the deposited composites. Composite electrodes exhibit significantly enhanced current density for hydrogen evolution in alkaline media compared to nickel Watts electrodes. Differential Electrochemistry Mass Spectrometry (DEMS) elucidates the hydrogen evolution mechanism, providing accurate data for Tafel plots. X-ray photoelectron spectroscopy (XPS) shows minimal impact on nickel's surface chemistry. X-ray diffractograms demonstrate that tungsten carbide particles maintain crystalline structure. X-ray dispersive spectroscopy (EDS) reveals an uneven chemical composition, with Ni/WC and Ni/W2C composites containing approximately 17% tungsten carbides. Electrochemical impedance spectroscopy (EIS) indicates higher electrochemical areas and lower charge transfer resistances in Ni/WC and Ni/W2C composites than in Ni Watts. This study contributes insights for the efficient and economical development of electrolysis systems. Notably, Ni/WC and Ni/W2C composites show promising electrochemical performance, emphasizing their potential in advancing electrolysis technology.

Polyolefin-derived substrate-grown carbon nanotubes as binder-free electrode for hydrogen evolution in alkaline media

Switching from a linear mode of waste management to a circular loop by transforming plastic waste into carbon nanotubes (CNTs) is a promising approach to current plastic waste treatment. One of the many applications of CNTs is its use for electrocatalytic water splitting for hydrogen evolution. Existing methods of CNTs-based hydrogen evolution reaction (HER) electrode fabrication involve additives like polymeric binders and additional steps to improve CNT dispersion, which are detrimental to the CNT structure and properties. The in-situ fabrication approach can potentially be a one-pot solution to HER electrode synthesis. In this study, polyolefins pyrolysis gas and a Co:Ni:Mg catalyst were used to fabricate binder-free CNTs-based electrodes on different substrates for HER. The study assessed CNT quality on conductive carbon paper, semiconductive silicon, and dielectric glass substrates, evaluating their HER performance in 1 M KOH. A mixture of hollow-core, bamboo-like, and cup-stacked arrangement nanotubes were synthesized on the substrates, with CNTs on glass and carbon paper substrates possessing better graphitization than CNTs grown on silicon. This is in agreement with HER performance, whereby the as-prepared electrodes required overpotentials of 267 mV, 241 mV, and 216 mV for silicon, glass, and carbon paper, respectively, to achieve 10 mA/cm2. Despite being poorly conductive, the glass substrate electrode achieved a lower overpotential than the silicon electrode. Additionally, the as-prepared silicon electrode faced a delamination issue likely attributed to the lower surface energy of the silicon substrate surface, demonstrating the weaker adhesion between the CNTs and silicon surface. The proposed approach thus showed that the in-situ fabricated electrodes performed better than separately synthesized CNTs prepared into electrodes by 27.4% and 14.2% for carbon paper and glass substrates, respectively. The improved performance of the as-prepared, binder-free electrodes can be linked to the lower charge-transfer resistance and reduced contact resistance between the CNTs and substrate.

Hierarchical CoO@MoN heterostructure nanowire array as a highly efficient electrocatalyst for hydrogen evolution

The high energy barrier and sluggish electron transfer are regarded as the most important reasons that restricting the performance of electrocatalysts for hydrogen evolution. The hierarchical CoO@MoN heterostructure nanowire array is fabricated, with adjusted electronic structure for tuning the binding strength of intermediates. As a result, CoO@MoN exhibits an excellent activity that is close to the benchmark Pt/C toward hydrogen evolution in alkaline medium. The theoretical computations indicate that the coupling of CoO and MoN can lead to the facilitated electron transfer for the tuned band structure. Besides, the energy barrier in the reaction is greatly reduced for the ameliorated binding strength of intermediates on CoO@MoN. This work demonstrates the significance of accelerating the electron transfer and reducing the energy barrier by rationally constructing the heterostructure, which paves the road to the exploitation of highly active and cost-efficient electrocatalysts for hydrogen evolution.

Ligand Modulation of Active Sites to Promote Cobalt-Doped 1T-MoS2 Electrocatalytic Hydrogen Evolution in Alkaline Media.

Highly efficient hydrogen evolution reaction (HER) electrocatalyst will determine the mass distributions of hydrogen-powered clean technologies, while still faces grand challenges. In this work, a synergistic ligand modulation plus Co doping strategy is applied to 1T-MoS2 catalyst via CoMo-metal-organic frameworks precursors, boosting the HER catalytic activity and durability of 1T-MoS2 . Confirmed by Cs corrected transmission electron microscope and X-ray absorption spectroscopy, the polydentate 1,2-bis(4-pyridyl)ethane ligand can stably link with two-dimensional 1T-MoS2 layers through cobalt sites to expand interlayer spacing of MoS2 (Co-1T-MoS2 -bpe), which promotes active site exposure, accelerates water dissociation, and optimizes the adsorption and desorption of H in alkaline HER processes. Theoretical calculations indicate the promotions in the electronic structure of 1T-MoS2 originate in the formation of three-dimensional metal-organic constructs by linking π-conjugated ligand, which weakens the hybridization between Mo-3d and S-2p orbitals, and in turn makes S-2p orbital more suitable for hybridization with H-1s orbital. Therefore, Co-1T-MoS2 -bpe exhibits excellent stability and exceedingly low overpotential for alkaline HER (118 mV at 10 mA cm-2 ). In addition, integrated into an anion-exchange membrane water electrolyzer, Co-1T-MoS2 -bpe is much superior to the Pt/C catalyst at the large current densities. This study provides a feasible ligand modulation strategy for designs of two-dimensional catalysts.

Ligand Modulation of Active Sites to Promote Cobalt‐Doped 1T‐MoS2 Electrocatalytic Hydrogen Evolution in Alkaline Media

AbstractHighly efficient hydrogen evolution reaction (HER) electrocatalyst will determine the mass distributions of hydrogen‐powered clean technologies, while still faces grand challenges. In this work, a synergistic ligand modulation plus Co doping strategy is applied to 1T−MoS2 catalyst via CoMo‐metal‐organic frameworks precursors, boosting the HER catalytic activity and durability of 1T−MoS2. Confirmed by Cs corrected transmission electron microscope and X‐ray absorption spectroscopy, the polydentate 1,2‐bis(4‐pyridyl)ethane ligand can stably link with two‐dimensional 1T−MoS2 layers through cobalt sites to expand interlayer spacing of MoS2 (Co−1T−MoS2‐bpe), which promotes active site exposure, accelerates water dissociation, and optimizes the adsorption and desorption of H in alkaline HER processes. Theoretical calculations indicate the promotions in the electronic structure of 1T−MoS2 originate in the formation of three‐dimensional metal‐organic constructs by linking π‐conjugated ligand, which weakens the hybridization between Mo‐3d and S‐2p orbitals, and in turn makes S‐2p orbital more suitable for hybridization with H‐1s orbital. Therefore, Co−1T−MoS2‐bpe exhibits excellent stability and exceedingly low overpotential for alkaline HER (118 mV at 10 mA cm−2). In addition, integrated into an anion‐exchange membrane water electrolyzer, Co−1T−MoS2‐bpe is much superior to the Pt/C catalyst at the large current densities. This study provides a feasible ligand modulation strategy for designs of two‐dimensional catalysts.

Constructing Ni4W/WO3/NF with strongly coupled interface for hydrogen evolution in alkaline media

Constructing Ni4W/WO3/NF with strongly coupled interface for hydrogen evolution in alkaline media

Hierarchical nanoarchitecture with NiFe-LDH on MoS2 for enhanced electrocatalysis of hydrogen evolution in alkaline media

Molybdenum disulfide (MoS2) can effectively improve the efficiency of hydrogen evolution reaction (HER) and reduce the cost of hydrogen production. However, MoS2 is kinetically sluggish in alkaline media, which makes it difficult to apply directly to HER. In order to improve the applicability of MoS2 in HER, this paper designs a hierarchical NiFe-LDH/MoS2 nanosheet with a heterogeneous interface anchored on carbon fiber paper (CFP) to optimize the performance of MoS2. The experimental results show that the NiFe-LDH/MoS2/CFP electrode in 1.0 M KOH exhibits excellent HER activity with only 88.5 mV overpotential at 10 mA cm−2. The good performance is attributed to numerous active sites on the NiFe-LDH/MoS2 heterogeneous surface, the good electrical conductivity of MoS2 and CFP, as well as the pores distributed on NiFe-LDH/MoS2 that facilitate mass transfer. It is also found that the catalyst exhibits outstanding stability (24 h) in alkaline media. This work opens up new prospects for the development of high-performance electrocatalysts in alkaline media.

In-situ construction of Mo2C–MoC heterostructure on Ni foam for efficient hydrogen evolution in alkaline media

Herein, a composite Mo2C–MoC heterostructured electrocatalyst is directly grown on Ni foam (NF) via the simple one-step annealing of MoCl5, urea, and NF under a flow of N2 at various temperatures for use in the hydrogen evolution reaction (HER). In the proposed synthetic method, the ratio of Mo2+ and Mo3+ in the Mo2C–MoC heterostructure, along with the HER performance, is greatly affected by the annealing temperature. In particular, the Mo2C–MoC/NF catalyst prepared at 650 °C exhibits a superior HER performance, with small overpotentials of 28.6 and 119.7 mV at 10 and 100 mA cm−2, respectively, along with great stability for 50 h in 1 M KOH. Notably, this is among the best performance results for recently reported molybdenum carbide-based catalysts. This is attributed to the interplay between the Mo2C–MoC heterostructure and the NF, whereby the former provides active sites by optimizing the hydrogen binding energy, while the latter provides a large surface area and high electrical conductivity.

Cactus-like amorphous MoS2-CoFeLDO heterostructures for alkaline hydrogen evolution reaction

Designing efficient and stable non-precious metal catalysts with heterogeneous structures for electrolytic hydrogen evolution in alkaline media is a challenging topic. Cactus-like amorphous MoS2-CoFeLDO heterostructures derived from calcination of MoS2-CoFeLDH in argon markedly reduced overpotential of hydrogen evolution reaction (HER). The HER overpotential of MoS2-CoFeLDO@400 °C in 1 M KOH solution required only 36 mV to reach a current density of 10 mA/cm2 and remained highly active for ≥24 h. Finite element simulations showed that cactus-like tip generated higher charge intensity, then aggregated electrons induced a higher electric field for local H+ enrichment. XRD and TEM analyses confirmed amorphous MoS2 with abundant hydrogen evolution sites in MoS2-CoFeLDO@400 °C. DFT calculations demonstrated that MoS2-CoO had a 0.5 eV lower reaction energy barrier than MoS2-CoFeLDH in the Tafel step, indicating superior reaction kinetics to promote HER.

Heterostructured CoFeP/CoP as an Electrocatalyst for Hydrogen Evolution in Alkaline Media.

Developing highly efficient and persistent transition-metal-phosphide (TMP)-based electrocatalysts is critical for the hydrogen evolution reaction (HER) via water splitting in alkaline media. Herein, we constructed a unique heterostructured CoFeP/CoP grown on a nickle foam (NF) via hydrothermal and dipping methods followed by phosphorization at different temperatures for HER. The experimental results exhibit that the HER activity of CoFeP/CoP-400 is accelerated after the construction of heterostructures. The unique heterostructure provides plentiful active sites and a large surface area, which are beneficial for HER in 1.0 M KOH. CoFeP/CoP-400 displays a small overpotential of 78 mV at a current density of 10 mA cm-2 and a smaller Tafel slope of 55.5 mV dec-1. Moreover, CoFeP/CoP-400 shows excellent stability with a long-term operating time of 12 h. This work provides an effective method for the construction of TMPs with heterostructures for promoting energy conversion.

Copper Phosphide Nanowires as High-Performance Catalysts for Urea-Assisted Hydrogen Evolution in Alkaline Medium.

Water electrolysis represented a promising avenue for the large-scale production of high-purity hydrogen. However, the high overpotential and sluggish reaction rates associated with the anodic oxygen evolution reaction (OER) posed significant obstacles to efficient water splitting. To tackle these challenges, the urea oxidation reaction (UOR) emerged as a more favorable thermodynamic alternative to OER, offering both the energy-efficient hydrogen evolution reaction (HER) and the potential for the treating of urea-rich wastewater. In this work, a two-step methodology comprising nanowire growth and phosphating treatment was employed to fabricate Cu3P nanowires on Cu foam (Cu3P-NW/CF) catalysts. These novel catalytic architectures exhibited notable efficiencies in facilitating both the UOR and HER in alkaline solutions. Specifically, within urea-containing electrolytes, the UOR manifested desirable operational potentials of 1.43 V and 1.65 V versus the reversible hydrogen electrode (vs. RHE) to reach the current densities of 10 and 100 mA cm-2, respectively. Concurrently, the catalyst displayed a meager overpotential of 60 mV for the HER at a current density of 10 mA cm-2. Remarkably, the two-electrode urea electrolysis system, exploiting the designed catalyst as both the cathode and anode, demonstrated an outstanding performance, attaining a low cell voltage of 1.79 V to achieve a current density of 100 mA cm-2. Importantly, this voltage is preferable to the conventional water electrolysis threshold in the absence of urea molecules. Moreover, our study shed light on the potential of innovative Cu-based materials for the scalable fabrication of electrocatalysts, energy-efficient hydrogen generation, and the treatment of urea-rich wastewater.