Alkaline Hydrogen Evolution Reaction Research Articles

Nitrogen-doped MoO2/Cu heterojunction electrocatalyst for highly efficient alkaline hydrogen evolution reaction

Metal/metal-(hydr)oxide heterojunction has been proposed as an efficient means to enhance the kinetics of alkaline hydrogen evolution reaction (HER). However, the poor electronic conductivity of metal-(hydr)oxides hinders the transport of electrons and the inappropriate electronic structure of the constituent phases would lower the HER activity. Herein, a nitrogen-doped MoO2/Cu heterostructure nanosheets was prepared by a simple hydrothermal and subsequent annealing treatment, acting as a model catalyst for element-doped modified metals/metal-oxides composite towards alkaline HER. Experimental results revealed that the HER catalytic activity of the catalyst was effectively improved by the nitrogen doping and the hetero coupling effect. The obtained N–MoO2/Cu catalyst exhibited a low overpotential of 40 and 363 mV to drive the current densities of 10 and 1000 mA cm−2, respectively, and showed high stability in the constant-current test of 50 h at 10 mA cm−2, 100 mA cm−2 and 1000 mA cm−2. Impressively, the N–MoO2/Cu catalyst coupled with Ni–Fe LDH to assemble an alkaline electrolyzer only require a voltage of 1.49 V to achieve a current density of 10 mA cm−2, and could be actuated by wind power to continuously produce hydrogen.

Identifying the Active Sites in MoSi2@MoO3 Heterojunctions for Enhanced Hydrogen Evolution.

Developing Two-dimensional (2D) Mo-based heterogeneous nanomaterials is of great significance for energy conversion, especially in alkaline hydrogen evolution reaction (HER), however, it remains a challenge to identify the active sites at the interface due to the structure complexity. Herein, the real active sites are systematically explored during the HER process in varied Mo-based 2D materials by theoretical computational and magnetron sputtering approaches first to filtrate the candidates, then successfully combined the MoSi2 and MoO3 together through Oxygen doping to construct heterojunctions. Benefiting from the synergistic effects between the MoSi2 and MoO3, the obtained MoSi2@MoO3 exhibits an unprecedented overpotential of 72mV at a current density of 10mA cm-2. Density functional theory calculations uncover the different Gibbs free energy of hydrogen adsorption (ΔGH*) values achieved at the interfaces with different sites as adsorption sites. The results can facilitate the optimization of heterojunction electrocatalyst design principles for the Mo-based 2D materials.

Island-in-Sea Structured Pt3Fe Nanoparticles-in-Fe Single Atoms Loaded in Carbon Materials as Superior Electrocatalysts toward Alkaline HER and Acidic ORR.

In this work, Pt3Fe nanoparticles (Pt3Fe NPs) with the ordered internal structure and Pt-rich shells surrounded by plenty of Fe single atoms (Fe SAs) as active species (Pt3Fe NP-in-Fe SA) loaded in the carbon materials are successfully fabricated, which are abbreviated as island-in-sea structured (IISS) Pt3Fe NP-in-Fe SA catalysts. Moreover, the synergistic effect of O-bridging between Pt3Fe NPs and Fe SAs, and the ordered internal structured Pt3Fe NPs with Pt-rich shells of an optimal thickness contributes to the achievement of the local acidic environments on the surfaces of Pt3Fe NPs in the alkaline hydrogen evolution reaction (HER) and the enhancement of the desorption rate of *OH intermediate in the acidic oxygen reduction reaction (ORR). In addition, the electronic interactions between Pt3Fe NPs and dispersed Fe SAs cannot only provide efficient electrons transfer, but also prevent the aggregation and dissolution of Pt3Fe NPs. Furthermore, the overpotential and the half wave potential of the as-prepared IISS Pt3Fe NP-in-Fe SA catalysts toward the alkaline HER and toward the acidic ORR are 8mV at a current density of 10mAcm-2 and 0.933V, respectively, which is 29 lower and 86mV higher than those (37mV and 0.847V) of commercial Pt/C catalysts.

Hydrogen‐Induced Disproportionation of Samarium‐Cobalt Intermetallics Enabling Promoted Hydrogen Evolution Reaction Activity and Durability in Alkaline Media

AbstractTransition‐metal nanoparticles hold great promise as electrocatalysts for alkaline hydrogen evolution reaction (HER), however, addressing the simultaneous challenges of ensuring sufficient active sites, promoting favorable water dissociation, and optimizing binding energy toward hydrogen intermediates remains a formidable task. To overcome these hurdles, a novel gaseous hydrogen engineering strategy is proposed by in situ embedding cobalt nanoparticles within a samarium hydride matrix (Co/SmH2) via hydrogen‐induced disproportionation of SmCo5 particles for efficient alkaline HER. The as‐designed Co/SmH2 delivered an overpotential as low as 252 mV at 100 mA cm−2, surpassing the performance of pristine Co by 100 mV. Notably, this catalyst lasts remarkably long maintaining a durability at ≈500 mA cm−2 for 120 h. A combination of in situ Raman spectroscopy, in situ X‐ray absorption spectroscopy, density functional theory calculation and post‐HER characterizations unambiguously unveiled that the surface SmH2 transforms into samarium (hydr)oxide during electrocatalysis. This transformation not only inhibits the aggregation of the ultrafine cobalt nanoparticles but also significantly enhances the water dissociation and optimizes the binding energy of active cobalt species toward hydrogen intermediate, resulting in concurrent improvement of kinetics, thermodynamics, and stability of the HER process.

In Situ Engineering Multifunctional Active Sites of Ruthenium-Nickel Alloys for pH-Universal Ampere-Level Current-Density Hydrogen Evolution.

Developing robust non-platinum electrocatalysts with multifunctional active sites for pH-universal hydrogen evolution reaction (HER) is crucial for scalable hydrogen production through electrochemical water splitting. Here ultra-small ruthenium-nickel alloy nanoparticles steadily anchored on reduced graphene oxide papers (Ru-Ni/rGOPs) as versatile electrocatalytic materials for acidic and alkaline HER are reported. These Ru-Ni alloy nanoparticles serve as pH self-adaptive electroactive species by making use of in situ surface reconstruction, where surface Ni atoms are hydroxylated to produce bifunctional active sites of Ru-Ni(OH)2 for alkaline HER, and selectively etched to form monometallic Ru active sites for acidic HER, respectively. Owing to the presence of Ru-Ni(OH)2 multi-site surface, which not only accelerates water dissociation to generate reactive hydrogen intermediates but also facilitates their recombination into hydrogen molecules, the self-supported Ru90Ni10/rGOP hybrid electrode only takes overpotential of as low as ≈106mV to deliver current density of 1000mAcm-2, and maintains exceptional stability for over 1000h in 1 m KOH. While in 0.5 m H2SO4, the Ru90Ni10/rGOP hybrid electrode exhibits acidic HER catalytic behavior comparable to commercially available Pt/C catalyst due to the formation of monometallic Ru shell. These electrochemical behaviors outperform some of the best Ru-based catalysts and make it attractive alternative to Pt-based catalysts toward highly efficient HER.

Effect of nickel sulfide catalysts with different morphologies on high efficiency alkaline hydrogen evolution reaction

An important area of research is the creation of non-precious metal catalysts with increased catalytic activity and stability for the electrolysis of water to produce hydrogen. A viable and effective method for altering the surface structure of electrocatalysts and improving their performance is morphology control. In this study, the amount of ammonium fluoride (NH4F) used in the hydrothermal process was changed to create a range of nickel sulfide (NiS) electrocatalysts with tunable morphologies. The improved NiS catalyst demonstrated exceptional performance in the hydrogen evolution process (HER) because of its expansive active area, elevated surface activity, and gas diffusion channels. In particular, it showed a low Tafel slope of 65.90 mV dec−1 in 1 M KOH electrolyte solution and an overpotential of 97 mV at a current density of 10 mA cm−2. Remarkably, the NiS electrocatalyst maintained its excellent HER performance even after 60-hour durability test. These findings underscore the significance and feasibility of morphology control in achieving desirable catalytic activity.

Gradient OH Desorption Facilitating Alkaline Hydrogen Evolution Over Ultrafine Quinary Nanoalloy

AbstractStrengthening OH adsorption on electrocatalyst is crucial to promote the rate‐determining water dissociation step of alkaline hydrogen evolution reaction (HER), whereas too‐intensified OH adsorption will poison the active sites instead. This dilemma remains one of the major challenges for improving the electrocatalysts’ alkaline HER activities. Herein, a surprising finding that the strongly adsorbed OH on an ultrafine quinary PtCoCuNiZn nanoalloy can be facilely desorbed via a unique gradient OH desorption pattern is reported, which tremendously boosts its alkaline HER activity. Theoretical simulations unravel that the ultrafine PtCoCuNiZn nanoalloy possesses versatile metal sites for adsorbing OH and the strongly adsorbed OH can be gradiently transferred to desorb from the ultrafine PtCoCuNiZn nanoalloy with moderate energy barriers for each transfer step that is the gradient OH desorption. In the meanwhile, the unique gradient OH desorption mode on the ultrafine PtCoCuNiZn nanoalloy is also experimentally evidenced by the in situ Raman spectroscopy and cyclic voltammetry measurements. This finding offers a fresh opportunity to expedite the alkaline HER without compromising the OH adsorption strength on electrocatalysts, which thus maximally promotes their water dissociation properties and unlocks the full potential of their alkaline HER activities.

Rational Design of Dynamic Interface Water Evolution on Turing Electrocatalyst toward the Industrial Hydrogen Production.

Manipulating the structural and kinetic dissociation processes of water at the catalyst-electrolyte interface is vital for alkaline hydrogen evolution reactions (HER) at industrial current density. This is seldom actualized due to the intricacies of the electrochemical reaction interface. Herein, this work introduces a rapid, nonequilibrium cooling technique for synthesizing ternary Turing catalysts with short-range ordered structures (denoted as FeNiRu/C). These advanced structures empower the FeNiRu/C to exhibit excellent HER performance in 1 m KOH with an ultralow overpotential of 6.5 and 166.2 mV at 10 and 1000 mA cm-2, respectively, and a specific activity 7.3 times higher than that of Pt/C. Comprehensive mechanistic analyses reveal that abundant atomic species form asymmetric atomic electric fields on the catalyst surface inducing a directed evolution and the dissociation process of interfacial H2O molecules. In addition, the locally topologized structure effectively mitigates the high hydrogen coverage of the active site induced by the high current density. The establishment of the relationship between free water population and HER activity provides a new paradigm for the design of industrially relevant high performance alkaline HER catalysts.

Tuning A-Site Cation Deficiency in Pr0.5La0.5BaCo2O5+ δ Perovskite to Realize Large-Scale Hydrogen Evolution at 2000mAcm-2.

Industrial-level hydrogen production from the water electrolysis requires reducing the overpotential (η) as much as possible at high current density, which is closely related to intrinsic activity of the electrocatalysts. Herein, A-site cation deficiency engineering is proposed to screen high-performance catalysts, demonstrating effective Pr0.5- xLa0.5BaCo2O5+ δ (P0.5- xLBC) perovskites toward alkaline hydrogen evolution reaction (HER). Among all perovskite compositions, Pr0.4La0.5BaCo2O5+ δ (P0.4LBC) exhibits superior HER performance along with unique operating stability at large current densities (J = 500-2000mAcm-2 geo). The overpotential of ≈636mV is achieved in P0.4LBC at 2000mAcm-2 geo, which outperforms commercial Pt/C benchmark (≈974mV). Furthermore, the Tafel slope of P0.4LBC (34.1mVdec-1) is close to that of Pt/C (35.6mVdec-1), reflecting fast HER kinetics on the P0.4LBC catalyst. Combined with experimental and theoretical results, such catalytic activity may benefit from enhanced electrical conductivity, enlarged Co-O covalency, and decreased desorption energy of H* species. This results highlight effective A-site cation-deficient strategy for promoting electrochemical properties of perovskites, highlighting potential water electrolysis at ampere-level current density.

Regulation of electron density redistribution for efficient alkaline hydrogen evolution reaction and overall water splitting

The rational design of morphology and heterogeneous interfaces for non-precious metal electrocatalysts is crucial in electrochemical water decomposition. In this paper, a bifunctional electrocatalyst (Ni/NiFe LDH), which coupling nickel with nickel–iron layer double hydroxide (NiFe LDH), is synthesized on carbon cloth. At current density of 10 mA cm−2, the Ni/NiFe LDH exhibits a low hydrogen evolution reaction (HER) overpotential of only 36 mV due to the accelerated electrolyte penetration, which is caused by superhydrophilic interface. Moreover, an alkaline electrolyzer is formed and provide a current density of 10 mA cm−2 with a voltage of only 1.49 V. It is confirmed by the density functional theory (DFT) that electron from the Ni layer is transferred to NiFe LDH layer, redistributing the local electron density around the heterogeneous phase interface. Thus, the Gibbs free energy for hydrogen adsorption is optimized. This work provides a promising strategy for the rational regulation of electrons at heterogeneous interfaces and the synthesis of flexible electrocatalysts.

Tafel Slope Plot as a Tool to Analyze Electrocatalytic Reactions.

Kinetic and nonkinetic contributions to the Tafel slope value can be separated using a Tafel slope plot, where a constant Tafel slope region indicates kinetic meaningfulness. Here, we compare the Tafel slope values obtained from linear sweep voltammetry to the values obtained from chronoamperometry and impedance spectroscopy, and we apply the Tafel slope plot to various electrocatalytic reactions. We show that similar Tafel slope values are observed from the different techniques under high-mass-transport conditions for the oxygen evolution reaction on NiFeOOH in 0.2 M KOH. However, for the alkaline hydrogen evolution reaction and the CO2 reduction reaction, no horizontal Tafel slope regions were observed. In contrast, we obtained the expected Tafel slope of 30 mV/dec for the HER on Pt in 1 M HClO4. We argue that widespread application of the Tafel slope plot, or similar numerical differentiation techniques, would result in an improved comparison of kinetic data for many electrocatalytic reactions when the traditional Tafel plot analysis is ambiguous.

Enhanced Alkaline Hydrogen Evolution Reaction via Electronic Structure Regulation: Activating PtRh with Rare Earth Tm Alloying.

Developing high-performance electrocatalysts for alkaline hydrogen evolution reaction (HER) is crucial for producing green hydrogen, yet it remains challenging due to the sluggish kinetics in alkaline environments. Pt is located near the peak of HER volcano plot, owing to its exceptional performance in hydrogen adsorption and desorption, and Rh plays an important role in H2O dissociation. Lanthanides (Ln) are commonly used to modulate the electronic structure of materials and further influence the adsorption/desorption of reactants, intermediates, and products, and noble metal-Ln alloys are recognized as effective platforms where Ln elements regulate the catalytic properties of noble metals. Here Pt1.5Rh1.5Tm alloy is synthesized using the sodium vapor reduction method. This alloy demonstrates superior catalytic activity, being 4.4 and 6.6 times more effective than Pt/C and Rh/C, respectively. Density Functional Theory (DFT) calculations reveal that the upshift of d-band center and the charge transfer induced by alloying promote adsorption and dissociation of H2O, making Pt1.5Rh1.5Tm alloy more favorable for the alkaline HER reaction, both kinetically and thermodynamically.

High-Performance MoP-Mo2C/C Heterogeneous Nanoparticle Catalysts for Alkaline Hydrogen Evolution and Oxidation Reactions

High-Performance MoP-Mo₂C/C Heterogeneous Nanoparticle Catalysts for Alkaline Hydrogen Evolution and Oxidation Reactions

Electrodeposition of Fractal Structured Nickel for Hydrogen Evolution Reaction in Alkaline

AbstractTo accelerate the practical application of water splitting in alkaline media, it is imperative to enhance the electrocatalytic performance for the Hydrogen Evolution Reaction (HER). In this context, we demonstrate that a simple (one‐pot, one‐step) electrodeposition process of nickel (Ni) in the presence of 3,5‐diamino1,2,4‐triazole (DAT) results in the formation of fractally structured Ni films with a significantly increased surface area. The Electrochemically active surface area (ECSA) increases with the electrodeposition charge passed, with the film electrodeposited at 14 C cm−2 achieving a reduction in overpotential at −10 mA cm−2 (η10) to 65.7 mV, coupled with a remarkable increase in ECSA (114‐fold greater than that of Ni‐foil). Additionally, nickel deposited in the presence of DAT effectively mitigates deactivation during electrolysis, exhibiting a 3.6‐fold lower overpotential degradation compared to that of the smooth Ni foil. This simple electrodeposition technique, applicable to a variety of conductive substrates, is distinguished by its high catalytic performance in the HER, a feature of considerable significance.

Introducing active sites and regulating electron distribution to design Mo and P co-doped Ni for efficient alkaline hydrogen evolution reaction

NiMoP electrocatalysts for hydrogen evolution reaction (HER) are received widespread concern, but the mechanism of Mo/P atoms for improving the HER activity still need to be revealed in details. Herein, we synthesize the Mo/P co-doped Ni (NMP) electrocatalysts, and the alkaline HER performances are tested. The NMP exhibit the excellent activity, durability and stability of material characters. Based on the results of experiments and density functional theory calculations, it is found that the introduced P atoms can regulate the electron redistribution, which can result in enhancing the reaction kinetic, increasing the active sites and charge exchange capacity. Besides, it leads the doped Mo to become the active site in both Volmer and Heyrovsky processes, and Ni bonded to Mo and Ni atoms exhibit the increasing activity. The obtained results display a deeper understanding for the doped metal and non-metallic atoms in enhancing HER activity of Ni, which is of great significant for designing the highly efficient and inexpensive electrocatalysts for producing hydrogen.

Well-defined ternary metal phosphide nanowires with stabilized Pt nanoclusters to boost alkaline hydrogen evolution reaction

Designing low-content and high-activity Pt-based catalysts with the high durability for the electrochemical hydrogen production remains a challenge. In this study, a ternary metal phosphide (NiCoP) with 1D nanowire (NW) and 2D nanosheet (NS) morphologies incorporating Pt clusters (denoted as Ptcluster-NiCoP@NF NWs and Ptcluster-NiCoP@NF NSs, respectively) was prepared using a hydrothermal–phosphorization–electrodeposition method. Based on the “tip effect” of NWs and a high electrochemical surface area, the as-prepared Ptcluster-NiCoP@NF NWs display better hydrogen evolution reaction (HER) performance, with a low overpotential of 65 mV at a high current density of 100 mA cm−2 and a low Tafel slope of 38.86 mV dec−1, than the Ptcluster-NiCoP@NF NSs, with an overportential of 95 mV at 42.53 mV dec−1. This indicates that the NiCoP NW-based support exhibits faster HER kinetics. The mass activity (11.47 A mgPt−1) of the Ptcluster-NiCoP@NF NWs is higher than that of commercial Pt/C catalysts. Significantly, the Ptcluster-NiCoP@NF NWs display excellent cyclic stability with negligible losses for 5000 cycles and 30-h tests at a high current of 500 mA cm−2.

Controlled synthesis of self-supportive hydrangea shaped Ni based hydroxide/phosphide for efficient overall water splitting and full pH hydrogen evolution

The exploration of efficient, robust and nonprecious transition metal electrocatalysts for electrochemical hydrolysis is urgently needed. Herein, we developed Ni(OH)2 with 3D nanoflower structure on the titanium mesh by a simple electrodeposition method. The Ni(OH)2/Ti exhibited excellent oxygen evolution reaction performance and achieved 10 mA cm−2 at 190 mV with fast kinetics in alkaline conditions. Ni2P, NiS2 and NiSe2 were prepared by solid-phase reaction, and the 3D nanoflower increased the open structure and greatly enhanced catalytic activity. The Ni2P/Ti electrode required an overpotential of 52, 88 and 109 mV to reach 10 mA cm−2 for hydrogen evolution reaction in acidic, alkaline and neutral media, respectively. The results of electrochemical measurements and mechanistic studies showed that the catalytic activity of HER: Ni2P > NiS2 > NiSe2 > Ni(OH)2. The Ni2P/Ti and Ni(OH)2/Ti electrodes were assembled into an integrated water splitting electrolytic cell. The water electrolysis device assembled with the Ni2P/Ti and Ni(OH)2/Ti electrodes only needed a low potential of 1.608 V to achieve 50 mA cm−2 in alkaline environment and was operated stably for 50 h.

Unravelling the role of work function difference on supported Ru nanoclusters for alkaline hydrogen evolution reaction

Fine tuning the work function difference (ΔΦ) between support and Ru which in turn affects the electron distribution of Ru is an effective method for the design of high-performance alkaline hydrogen evolution reaction (HER) catalysts. However, it remains a challenge to understand the intrinsic relationship between HER activity and ΔΦ at the atomic level. Herein, taking N doped graphene supported Ru nanoclusters (Ru/CxNy) as the theoretical model, we demonstrate that the HER activity can be correlated with the variation of ΔΦ. For Ru/C50 with smaller ΔΦ, we find that the Ru atoms located at the top layer of Ru nanoclusters (Ru-t) with lower coordination numbers are the main reaction sites. For Ru/C30N20 with larger ΔΦ, the stronger charge redistributions of Ru is observed, and the electron-deficient Ru atoms closing to the interface (Ru-i) are the main reaction sites with significant improvement HER activity. Our findings demonstrate the role of ΔΦ on Ru/CxNy systems for the alkaline HER, which can provide valuable theoretical guidance for the design of high efficient HER catalysts.

Theoretical and experimental study of flower-like NiMoS/NiO/NF with interface layer as a novel highly efficient bifunctional-electrode toward supercapacitor and HER

Electrocatalytic water splitting and supercapacitor systems are considered one of the most imperative sustainable energy storage and conversion technologies as an alternative clean energy carrier/source to fossil fuels in order to address the pressing global warming problems. For achieving sustainable electrochemistry devices, highly efficient and superior durability electrocatalysts must be prepared through a facile and controllable approach. This study successfully demonstrated the development of a binder-free 3D- flower-like amorphous structure composite with self-assembled nanosheets supported on Nickel foam (NiMoS/NiO/NF) by a simple two-step hydrothermal technique as advanced electrocatalysts for alkaline hydrogen evolution reaction (HER) and supercapacitor. The as-obtained NiMoS/NiO/NF only needs a overpotential of 43 mV vs. RHE to reach 10 mA.cm−2 and remained stable after long-term HER tests. In the following, the nanostructure was operated as an electrode in the supercapacitor. According to the Galvanostatic Charge-Discharge (GCD) teats, the specific capacitance of NiMoS/NiO/NF was measured as 999F/g. Such outstanding NiMoS/NiO/NF performance can be ascribed to the synthesis of the interface layer (NiO), which makes the robust adhesion between NF and the final layer (NiMoS). The amorphous morphology with multi-component doping and heterojunctions, optimizes the hydrogen desorption sites, which leads to significant HER catalytic activity. The present experimental results and density functional theory (DFT) study offer a cost-effective, and convenient pathway to produce highly efficient non-nobel-based metal as high-valued multifunctional materials.

Toward boosted alkaline hydrogen evolution reaction: Covalent organic framework-derived N-doped carbon for highly dispersed cobalt nanoparticles

The preparation of renewable hydrogen via electrocatalytic water splitting is a burgeoning strategy in developing sustainable energy. However, it is still a great challenge to prepare an efficient non-precious metal based electrocatalyst for hydrogen evolution in alkaline electrolysis. Herein, we describe a functional hydrogen evolution reaction (HER) electrocatalyst by the combination of soaking metal ions in covalent organic framework (COF) and high temperature calcination. Especially, the 2Co-NC-700 catalyst possesses large specific surface area, appropriate defective nature and structural distortion, thus it embodies outstanding HER catalytic activity with only an overpotential of 303 mV at the current density of 10 mA cm−2 in the solution of 1.0 M KOH. Moreover, the kinetics and durability are also confirmed. Theoretical calculations not only indicates that the stable configuration combined small-sized cobalt nanoparticles and nitrogen-doped carbon but also reveals the synergistic effect of multiple active sites, while the optimal active location that shows the lowest hydrogen adsorption free energy is a major contributor for excellent HER. This work not only offers a highly efficient HER catalyst in alkaline environment but also provides a novel approach to develop non-precious metal nitrogen-doped carbon materials derived from COF as HER electrocatalysts in alkaline media.