Enhanced Alkaline Hydrogen Evolution Reaction Research Articles

Polyvinylpyrrolidone gel based Pt/Ni(OH)2 heterostructures with redistributing charges for enhanced alkaline hydrogen evolution reaction

Based on the synergy between PVP gel and Pt/Ni(OH)2 heterostructure, Pt/Ni(OH)2 heterostructure encapsulated in PVP gel was synthesized with an overpotential of 12 mV, Tafel slope of 21.5 mV dec−1, and stability for 50 h in alkaline solution.

Accelerating water dissociation kinetic in Co9S8 electrocatalyst by mn/N Co-doping toward efficient alkaline hydrogen evolution

Electrocatalytic hydrogen evolution under alkaline media holds great promising in hydrogen energy production. Transition-metal sulfides (TMSs) are attractive for electrocatalytic alkaline hydrogen evolution, yet their catalytic performance is unsatisfactory owing to the sluggish water dissociation kinetics. Herein, a Mn/N co-doping strategy is proposed to regulate the water dissociation kinetics of Co9S8 nanowires array grown on nickel foam thus improve the activity of hydrogen evolution reaction (HER). The optimal Mn/N co-doping Co9S8 (Mn–N–Co9S8) catalyst achieves low overpotentials of 102 and 238 mV at 10 and 100 mA cm−2 in the 1 M KOH solution, respectively, remarkably higher than the single-doping Mn–Co9S8 and N–Co9S8 as well as superior to many reported Co9S8-based HER electrocatalysts. Density functional theory (DFT) calculation results confirm that the water dissociation barrier of the Mn–N–Co9S8 is reduced significantly owing to the synergistic co-doping of Mn and N, which accounts for the enhanced alkaline HER performance. This study offers an effective strategy to enhance the alkaline HER activity of TMSs by accelerating water dissociation kinetic via the cation and anion co-doping strategy.

Melamine-assisted synthesis of ultrafine Mo2C/Mo2N@N-doped carbon nanofibers for enhanced alkaline hydrogen evolution reaction activity

Noble metal-free electrocatalysts with high activity are highly desirable for the large-scale application of hydrogen evolution reaction (HER). Mo2C-based nanomaterials have been proved as a promising alternative to noble metal-based electrocatalysts owing to the Pt-resembled d-band density and optimal intermediates-adsorption properties. However, the aggregation and excessive growth of crystals often occur during their high-temperature synthesis procedure, leading to low catalytic utilization. In this study, the ultrafine Mo2C/Mo2N heterostructure with large surface and interface confined in the N-doped carbon nanofibers (N-CNFs) was obtained by a melamine-assisted method. The synergistic effect of Mo2C/Mo2N heterostructure and plenty active sites exposed on the surface of ultrafine nanocrystals improves the electrocatalytic activity. Meanwhile, the N-CNFs ensure fast charge transfer and high structural stability during reactions. Moreover, the in-situ synthesis method strengthens the interfacial coupling interactions between Mo2C/Mo2N heterostructure and N-CNFs, further enhancing the electronic conductivity and electrocatalytic activity. Owing to these advantages, Mo2C/Mo2N@N-CNFs exhibit excellent HER performance with a low overpotential of 75 mV at a current density of 10 mV cm−2 in alkaline solution, superior to the single phased Mo2C counterpart and recently reported Mo2C/Mo2N based catalysts. This study highlights a new effective strategy to design efficient electrocatalysts via integrating heterostructure, nanostructure and carbon modification.

Interface engineered NiMoN/Ni3N heterostructures for enhanced alkaline hydrogen evolution reaction

The development of low-cost and high-efficiency hydrogen evolution reaction (HER) catalysts for alkaline electrolysis is beneficial in the storage of renewable electricity through hydrogen energy. Metallic Ni3N is regarded as an excellent catalyst for water oxidation, but the HER activity in alkaline solution is subjected to its poor water dissociation ability and strong hydrogen adsorption. In this work, we report a highly active and durable alkaline HER electrocatalyst of NiMoN/Ni3N heterostructures by interface engineering. The introduction of NiMoN can not only effectively accelerate the water dissociation process, but also optimize the binding energy of hydrogen via interfacial interaction with Ni3N. In addition, the porous nanosheet arrays assembled by plenty of nanoparticles can provide more exposed active sites and accelerate the reaction kinetics. The heterostructured electrocatalyst exhibits an extremely low overpotential of 28 mV at a current density of 10 mA cm−2 and a small Tafel slope of 49 mV dec−1. The design concept of interface engineering could offer a new paradigm for the development of superior HER catalysts toward alkaline electrolysis.

Structure design of MoS2@Mo2C on nitrogen-doped carbon for enhanced alkaline hydrogen evolution reaction

Non-precious metal-based electrocatalyst with high activity and stability for efficient hydrogen evolution reaction (HER) is of critical importance toward low-cost and large-scale water splitting. Traditional MoS2 has electrocatalytic hydrogen evolution inertness in alkaline environment, which is detrimental to the adsorption and dissociation of water. Composited with electrocatalyst with good electrical conductivity can enhance its HER activity. In this work, we for the first time construct a carbon-supported hollow heterostructure MoS2@Mo2C composite via two-step calcination and sulfurized process from carbonized Mo2C–Mo3C2 heteronanowires. The results show that the existence of the Mo3C2 phase is the key point to construct the effective heterostructure with hollow morphology. Due to the strong negative hydrogen binding energy for H on surface of Mo2C, the H+ reduction in the MoS2@Mo2C in the Volmer step can be enhanced. Compared with MoS2, MoS2@Mo2C has high electrocatalytic activity for hydrogen evolution with an onset potential of 28 mV, overpotential of 129 mV at the current density of 10 mA cm−2, a small Tafel slope of 78 mV dec−1, and an excellent stability. This work will provide new insights into the design of high-efficiency HER catalysts via interfacial engineering at nanoscale for commercial water splitting.

Hierarchical heterostructured nickle foam–supported Co3S4 nanorod arrays embellished with edge-exposed MoS2 nanoflakes for enhanced alkaline hydrogen evolution reaction

Transition metal chalcogenides with abundant active edge sites and suitable structures for large-scale water splitting in alkaline hydrogen evolution reaction (HER) are challenging but promising. Herein, hierarchical heterostructured nickel foam–supported Co3S4 nanorod arrays embellished with edge-exposed MoS2 nanoflakes (Edge-MoS2/Co3S4@NFs) as an effective HER catalyst are designed. There into, porous nickel foam and moderately distributed nanorod arrays of Edge-MoS2/Co3S4@NFs provide multiscale pathways for efficient charge and mass transport and significantly enlarge the surfaces for the deposition of MoS2 flakes. The superhydrophilic/aerophobic surface improves the electrolyte transport and facilitates the detachment of hydrogen bubbles from the surface of the catalyst. The MoS2 flakes anchored on nanorods are well dispersed with plentiful active sites exposed which enhance the intrinsic activity of active sites owing to the adequate intersection of charge and mass. In addition, there is a synergetic effect of bimetal sulfides, evidenced by increasing the turnover frequency. Therefore, the Edge-MoS2/Co3S4@NF affords a low overpotential (η10 = 90.3 mV and η1000 = 502.0 mV) and small Tafel slope (61.69 mV dec−1). This study provides a facile strategy to develop electrocatalysts through the synergy of enhanced thermodynamic and kinetic processes, shedding lights on the advanced design of functional materials for energy chemistry.

Interface construction of P-Substituted MoS2 as efficient and robust electrocatalyst for alkaline hydrogen evolution reaction

Molybdenum disulfide is known as a promising candidate for Pt-based catalysts in the hydrogen evolution reaction (HER), while the lack of the active-edge-site in-plane dominantly limits their intrinsic activity. Herein, a new strategy is reported to synthesize interface construction between MoS 2 and MoP, derived from the partial phosphidation of MoS 2 by incorporating P source (MoS 2 –MoP/NC). As a novel interface engineering electrode, MoS 2 –MoP/NC exhibits not only Pt-like catalytic activity but robust durability in alkaline electrolyte. Experiments and density functional theory (DFT) calculations certify that the formation of S vacancies on MoS 2 basal plane are facilitated by interlayer-interface construction between MoS 2 and MoP. Due to the delocalized electron inside S vacancies, the exposed coordination-unsaturated Mo atoms of S-defected MoS 2 offer active sites for water adsorption and activation, which accelerates the water dissociation steps. On the other hand, MoP provides active sites for hydrogen formation and desorption, which could weaken the adsorption strength of atomic hydrogen through van der Waals force of interlayer-interface. Our results show that the origin of the enhanced alkaline HER catalytic performance of MoS 2 –MoP/NC comes from the introduction of new active sites by interface construction, which provides an insight into the development of interlayer-interface engineering on MoS 2 . It is expected that this interface construction strategy can be extended to other 2D metal sulfides for enhancing their electrocatalytic activity. • An interface construction between MoS 2 and MoP (MoS 2 –MoP/NC) was synthesized for HER. • MoS 2 –MoP/NC exhibits Pt-like HER activity and robust durability in alkaline solution due to the interface effect. • The interface can introduce new active sites by creating S vacancies and exposing coordination-unsaturated Mo atoms. • Coordination-unsaturated Mo atoms can strength H 2 O adsorption and decrease H 2 O dissociation barrier. • MoP provides sites for hydrogen formation and desorption, promoted by weakening atomic hydrogen adsorption.

Surface engineering of CeO2–TiO2 composite electrode for enhanced electron transport characteristics and alkaline hydrogen evolution reaction

Herein, we report the fine tuning of electrocatalytic characteristics of CeO2–TiO2 composite by surface engineering to reduce overpotential and to improve exchange current density for enhanced alkaline hydrogen evolution reaction (HER). The enhanced electrocatalytic activity of the surface engineered CeO2–TiO2 composite through Ni and P decoration is attributed to the improved electron transport ability. The surface roughness characteristics and surface composition of electroactive species are tuned to generate high electronic conductivity on the surface engineered composite electrode surface. The developed hard electrode with leptokurtic surface (Sku > 3) exhibited a high average roughness value (Sa) of 3 μm due to incorporation of the mesoporous catalyst material into it. Tuning of a compact and continuous electrode surface with critical composition of elements Ni (52 at.%), P (20 at.%), Ce (9 at.%) and Ti (8 at.%) furnishes the high conductivity (contact potential difference = 0.83 V) to the electrode. The developed electrode with surface engineered CeO2–TiO2 catalyst exhibited a low overpotential of −111 mV (at a high current density of 250 mA cm−2) and high exchange current density (1.6 × 10−1 mA cm−2) with low charge transfer resistance (615 Ω cm2). High electrocatalytic activity and stability of the surface engineered CeO2–TiO2 catalyst electrode during alkaline (32 w/v.% NaOH) HER ensure its promising performance and applicability for long term HER.

Vertically aligned NiS2/CoS2/MoS2 nanosheet array as an efficient and low-cost electrocatalyst for hydrogen evolution reaction in alkaline media

Recently, the rational design of non-precious metal electrocatalysts for highly efficient hydrogen evolution reaction (HER) in alkaline media has received considerable interests in sustainable and renewable energy researches. Herein, vertically aligned and interconnected NiS2/CoS2/MoS2 nanosheet arrays on Ni foam were prepared by a two-step procedure that conducted by the hydrothermal synthesis of Ni-Co molybdate nanosheet array as the precursor and followed by the vapor phase sulfurization to achieve in situ conversion. Basing on the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations, it can be found that the honeycomb-like structure of the Ni-Co molybdate nanosheet array was well preserved after the sulfurization process. The high-resolution TEM (HRTEM) characterization reveals that the NiS2/CoS2/MoS2 nanosheet array provided abundant well-exposed active edge sites and multiple heterointerfaces towards enhanced alkaline HER performance. Electrochemical studies demonstrated that the ultrathin NiS2/CoS2/MoS2 nanosheets exhibited excellent HER performance with an overpotential of 112 mV at 10 mA cm−2 and a smaller Tafel slope of 59 mV dec−1 in comparison with NiS2/MoS2 (155 mV and 89 mV dec−1) and CoS2/MoS2 (124 mV and 75 mV dec−1) samples by taking the advantage of the well-exposed multiple heterointerfaces. This work presents a facile and reliable synthetic strategy for the rational design of highly efficient electrocatalysts for the HER in alkaline solution based on non-precious metal sulfide nanocomposite.

Promoting Alkaline Hydrogen Evolution Activity Using Ordered Mesoporous Α-MoC1−X Supported Pt Catalysts

The sluggish reaction kinetics of the alkaline hydrogen evolution reaction (HER) remains to be overcome for the commercialization of water-alkali electrolyzers [1, 2]. In this work, we demonstrate that the metastable face-centered-cubic (fcc) α-MoC1−x phase shows superior water dissociation capability and alkaline HER activity than thermodynamically stable, hexagonal-close-packed β-Mo2C phase. In order to design high surface area fcc α-MoC1−x , an ordered mesoporous α-MoC1−x (MMC) was synthesized by a nanocasting method. In the MMC structure, the α-MoC1−x phase facilitates the water dissociation reaction, while the mesoporous structure enables high dispersion of metal nanoparticles (NPs) and efficient mass transport. As a result, Pt NPs supported on the MMC (Pt/MMC) catalyst showed substantially enhanced alkaline HER activity in terms of overpotentials, Tafel slopes, mass and specific activities, and exchange current densities, compared to those of commercial Pt/C and Pt NPs supported on particulate α-MoC1−x or β-Mo2C. In particular, the Pt/MMC shows a very low Tafel slope of 30 mV dec−1, which is the lowest value among the reported Pt-based alkaline HER catalysts, suggesting the critical role of MMC in enhancing the HER kinetics. Furthermore, Pt/MMC exhibited almost no current decay for after potential cycling test whereas Pt/C underwent a negative shift of polarization curve. The promoting effect of MMC support in the alkaline HER was further demonstrated with an Ir/MMC catalyst.

Electrocatalytically inactive SnS2 promotes water adsorption/dissociation on molybdenum dichalcogenides for accelerated alkaline hydrogen evolution

Molybdenum dichalcogenides, in particular, MoS2 and MoSe2, are very promising nonprecious metal-based electrocatalysts for hydrogen evolution reaction (HER) in acidic media. They exhibit inferior alkaline HER activity, however, due to the sluggish water dissociation process. Here, we design and synthesize new molybdenum dichalcogenide-based heterostructures with the basal planes decorated with SnS2 quantum dots towards enhanced alkaline HER activity. The electrochemical results reveal that the alkaline hydrogen evolution kinetics of molybdenum dichalcogenides is substantially accelerated after incorporation of SnS2 quantum dots. The optimal MoSe2/SnS2 heterostructure delivers a much lower overpotential of 285 mV than MoSe2 (367 mV) to reach a current density of 10 mA cm−2 in 1 M KOH. The improved catalytic activity is predominantly owing to the enhanced water dissociation kinetics of the heterostructures with well-defined interfaces. Density functional theory (DFT) calculations reveal that the presence of SnS2 significantly promotes the water adsorption capability of MoSe2 nanosheets, which consequently facilitates the subsequent water dissociation process. These results open up a new avenue for the rational design of well-defined heterostructures with enhanced water adsorption/dissociation capability for the development of high-performance alkaline HER electrocatalysts.

Ordered Mesoporous Metastable α‐MoC1−x with Enhanced Water Dissociation Capability for Boosting Alkaline Hydrogen Evolution Activity

AbstractThe sluggish reaction kinetics of the alkaline hydrogen evolution reaction (HER) remains an important challenge for water–alkali electrolyzers, which originates predominantly from the additional water dissociation step required for the alkaline HER. In this work, it is demonstrated theoretically and experimentally that metastable, face‐centered‐cubic α‐MoC1−x phase shows superior water dissociation capability and alkaline HER activity than stable, hexagonal‐close‐packed Mo2C phase. Next, high surface area ordered mesoporous α‐MoC1−x (MMC) is designed via a nanocasting method. In MMC structure, the α‐MoC1−x phase facilitates the water dissociation reaction, while the mesoporous structure with high surface area enables a high dispersion of metal NPs and efficient mass transport. As a result, Pt nanoparticles (NPs) supported on MMC (Pt/MMC) show substantially enhanced alkaline HER activity in terms of overpotentials, Tafel slopes, mass and specific activities, and exchange current densities, compared to commercial Pt/C and Pt NPs supported on particulate α‐MoC1−x or β‐Mo2C. Notably, Pt/MMC shows very low Tafel slope of 30 mV dec–1, which is the lowest value among the reported Pt‐based alkaline HER catalysts, suggesting the critical role of MMC in enhancing the HER kinetics. The promotional effect of MMC support in the alkaline HER is further demonstrated with an Ir/MMC catalyst.

Double‐Site Ni–W Nanosheet for Best Alkaline HER Performance at High Current Density >500 mA cm−2

AbstractThe efficiency of the alkaline hydrogen evolution reaction (HER) has remained limited. Herein, a bimetallic Ni–W catalyst fabricated by the rapid dehydration of W‐doped Ni(OH)2 is reported. The Ni–W surface exhibits the following merits for an enhanced alkaline HER: a greater number of vacant outer d‐orbitals, better discharge characteristics, and a more significant difference in H adsorption between W and Ni atoms. The free water molecules are adsorbed onto W sites, then dissociated into *OH and *H. While *OH is released into the solution, *H is re‐adsorbed by nearby Ni sites. The synergistic effect of the Ni–W surface sites imparts this catalyst with the highest activity and the best stability at high current density. Specifically, at a current density of 500 mA cm‐2, the Ni–W catalyst reduces the overpotential to 303 mV, compared with 409 mV for the state‐of‐the‐art Pt/C catalyst. Additionally, the Ni–W catalyst exhibits better long‐term stability than the state‐of‐the‐art Pt/C. Whereas the Pt activity decreases by 181 mA cm‐2 after 31 h of testing at 500 mA cm‐2, the Ni–W loses only 55 mA cm‐2 under the same conditions. Density functional theory (DFT) calculations confirm the synergistic mechanism, which can be useful for general alkaline HER processes.

CoSe2 /MoSe2 Heterostructures with Enriched Water Adsorption/Dissociation Sites towards Enhanced Alkaline Hydrogen Evolution Reaction.

Transition-metal dichalcogenides (TMDs) are promising electrocatalysts toward the hydrogen evolution reaction (HER) in acid media, but they show significantly inferior activity in alkaline media due to the extremely sluggish water dissociation kinetics. Herein, CoSe2 /MoSe2 heterostructures with CoSe2 quantum dots anchored on MoSe2 nanosheets are synthesized towards enhanced alkaline HER catalytic activity. The incorporation of CoSe2 is intended to construct additional water adsorption sites on the basal planes of MoSe2 to promote water dissociation. The CoSe2 /MoSe2 heterostructures show substantially enhanced activity over MoSe2 and CoSe2 in 1 m KOH. The optimal overpotential required to reach a current density of 10 mA cm-2 is merely 218 mV, which is more than 100 mV greater than that of MoSe2 , which is by far the best performance demonstrated for precious-metal-free catalysts. Detailed analyses based on electrochemical testing demonstrate that the water adsorption and subsequent dissociation process is accelerated by CoSe2 species with rich edge sites; meanwhile, MoSe2 species provide sufficient active sites for the adsorption and combination of adsorbed hydrogen (H. ). These results provide an effective strategy for developing earth-abundant catalysts with high activity for the alkaline HER, and are of great significance to promote the practical application of alkaline water electrolysis.

Ultrathin Transition Metal Dichalcogenide/3d Metal Hydroxide Hybridized Nanosheets to Enhance Hydrogen Evolution Activity.

The vast majority of the reported hydrogen evolution reaction (HER) electrocatalysts perform poorly under alkaline conditions due to the sluggish water dissociation kinetics. Herein, a hybridization catalyst construction concept is presented to dramatically enhance the alkaline HER activities of catalysts based on 2D transition metal dichalcogenides (TMDs) (MoS2 and WS2 ). A series of ultrathin 2D-hybrids are synthesized via facile controllable growth of 3d metal (Ni, Co, Fe, Mn) hydroxides on the monolayer 2D-TMD nanosheets. The resultant Ni(OH)2 and Co(OH)2 hybridized ultrathin MoS2 and WS2 nanosheet catalysts exhibit significantly enhanced alkaline HER activity and stability compared to their bare counterparts. The 2D-MoS2 /Co(OH)2 hybrid achieves an extremely low overpotential of ≈128 mV at 10 mA cm-2 in 1 m KOH. The combined theoretical and experimental studies confirm that the formation of the heterostructured boundaries by suitable hybridization of the TMD and 3d metal hydroxides is responsible for the improved alkaline HER activities because of the enhanced water dissociation step and lowers the corresponding kinetic energy barrier by the hybridized 3d metal hydroxides.

Controllable Surface Reorganization Engineering on Cobalt Phosphide Nanowire Arrays for Efficient Alkaline Hydrogen Evolution Reaction.

Developing highly efficient hydrogen evolution reaction (HER) catalysts in alkaline media is considered significant and valuable for water splitting. Herein, it is demonstrated that surface reorganization engineering by oxygen plasma engraving on electocatalysts successfully realizes a dramatically enhanced alkaline HER activity. Taking CoP nanowire arrays grown on carbon cloth (denoted as CoP NWs/CC) as an example, the oxygen plasma engraving can trigger moderate CoOx species formation on the surface of the CoP NWs/CC, which is visually verified by the X-ray absorption fine structure, high-resolution transmission electron microscopy, and energy-dispersive spectrometer (EDS) mapping. Benefiting from the moderate CoOx species formed on the surface, which can promote the water dissociation in alkaline HER, the surface reorganization of the CoP NWs/CC realizes almost fourfold enhanced alkaline HER activity and a 180 mV decreased overpotential at 100 mA cm-2 , compared with the pristine ones. More interestingly, this surface reorganization strategy by oxygen plasma engraving can also be effective to other electrocatalysts such as free-standing CoP, Co4 N, O-CoSe2 , and C-CoSe2 nanowires, which verifies the universality of the strategy. This work thus opens up new avenues for designing alkaline HER electrocatalysts based on oxygen plasma engraving.