Hydrogen Evolution Reaction Process Research Articles

Sub-2.5 nm monodisperse Mo2C nanoparticles on N-doped carbon: The facet engineering for boosting electrochemical hydrogen evolution

Molybdenum carbide materials have demonstrated remarkable potential in catalyzing the hydrogen evolution reaction (HER). However, further modulation of their performance through simultaneously engineering the size and surface crystal facets remains challenging. Herein, we report the successful fabrication of N-doped carbon-supported monodisperse Mo2C nanoparticles with a size of ∼2.06 nm, exhibiting co-exposed (101)/(102) facets-heterojunction, derived from annealing glycine and ammonium molybdate tetrahydrate. The optimized Mo2C/NC-Amt catalyst exhibits a low overpotentials of 128 mV to achieve the current density of 10 mA cm−2 and a small Tafel slope of 72 mV dec−1 under alkaline solution. By changing the molybdate precursor, the phase and crystal facet composition of molybdenum carbide can be effectively tuned, which provides a good platform for studying their structure-activity in HER. The theoretical calculations reveal the synergistic effect of (101)/(102) facets-heterojunction accelerates electron transfer and regulates the d band center of Mo2C, reducing the reaction barriers of intermediates in the HER process, thus significantly boosting reaction activity. This work proposes a novel insight into the rational fabrication of efficient HER catalysts through facet engineering toward heterojunction construction under the 2.5 nm region.

Transient Electro‐Graphitization of MOFs Affecting the Crystallization of Ruthenium Nanoclusters for Highly Efficient Hydrogen Evolution

AbstractFine control over the graphitization level of carbonized nanostructures can play a strategic role in tuning the crystallization of supported nanocatalysts, thereby modulating the kinetics of catalysis. However, realizing the synergistic interplay of graphitization‐tunable support and supported catalysts poses a significant challenge. This study proposes a current pulse‐induced ultrafast strategy for developing MOF‐derived graphitic nano‐leaves (GNL) and supported ultrafine ruthenium nanoclusters exhibiting selective crystallization states depending on the tunable graphitization level of GNL. The resulting ultrafine (≈0.7 nm) amorphous‐ruthenium nanoclusters linked with GNL (a‐Ru@GNL500) exhibit state‐of‐the‐art performance in the hydrogen evolution reaction (HER), requiring very low overpotentials of only 23.0 and 285.0 mV to achieve current densities of 10 and 500 mA cm−2, respectively. Furthermore, a‐Ru@GNL500 demonstrates exceptional operational stability for 100 h under high HER currents of 200 and 400 mA cm−2. Density functional theory reveals that the unique electronic structure of a‐Ru and the cooperative effect of cobalt embedded in the graphitic layer lower the occupancy of the antibonding orbital, resulting in an accelerated HER process. Additionally, the unique electronic structure, highly conducting GNL, and efficient bubble release dynamics of super‐aerophobic a‐Ru@GNL500 contribute to reduced overpotentials, particularly at high HER current densities.

Hydrogenation of Covalent Organic Framework Induces Conjugated π Bonds and Electronic Topological Transition to Enhance Hydrogen Evolution Catalysis.

Recently, many topological materials have been discovered as promising electrocatalysts in chemical conversion processes and energy storage. However, it remains unclear how the topological electronic states specifically modulate the catalytic reaction. Here, the two-dimensional metal phthalocyanine-based covalent organic framework (MPc-COF) is studied by ab initio thermodynamic calculations to clearly reveal the promotional effect on the electrochemical hydrogen evolution reaction (HER) induced by topological gapless bands (TGBs). We find that the prehydrogenated (and fluorinated) H4CdPc-COF(F) shows the best HER performance, with 0.016 V (near zero) overpotential. By tracking changes to the electronic structure and free energy as the prehydrogenation and HER processes occur, we are able to separately attribute the high HER efficiency in part due to the increase of the electron bath by donating electrons to the conjugated π bonds and also to the existence of TGBs. Specifically, the significant catalytic promotion by TGBs is proven to decrease the free energy by 0.218 eV to near zero. When the TGBs are destroyed, e.g., by replacing N with P and opening a band gap, the HER efficiency is reduced. This study opens avenues for deterministically harnessing topological band features to improve electrocatalysis.

Interface Engineering of Mo‐doped Ni2P/FexP‐V Multiheterostructure for Efficient Dual‐pH Hydrogen Evolution and Overall Water Splitting

AbstractDeveloping highly effective transition metal‐based bifunctional electrocatalysts remains a tremendously challenging task for large‐scale overall water splitting. Herein, a multiheterostructured Mo‐doped Ni2P/FexP electrocatalyst on NiFe foam with P vacancy (denoted as Mo─Ni2P/FexP‐V/NFF) is developed to serve as an efficient dual‐pH electrocatalyst. Due to the synergistic effect of multiple strategies (heteroatom doping, heterointerface, and P vacancy), the Mo─Ni2P/FexP‐V/NFF possesses remarkable hydrogen evolution reaction (HER) catalytic activity in alkaline/acidic and excellent oxygen evolution reaction (OER) in alkaline media, along with encouraging durability. The mechanisms of improved electrocatalytic activity combining multicharacterizations and density functional theory (DFT) calculations are elucidated. Specifically, X‐ray absorption fine structure experimental analysis confirms that the Mo doping can optimize the electronic structure of electrocatalyst. In situ Raman spectroscopy demonstrates that the evolved oxyhydroxides are the real active substances for the OER. DFT calculations reveal that the conductivity of as‐prepared samples can be enhanced through multiple strategy synergy. Moreover, in the HER process, multiple strategies can not only reduce the hydrogen binding energy to near zero but also enhance the H2O dissociation and *OH desorption. In the OER process, DFT calculations also verify that Mo doping and interface engineering can optimize the adsorption of the rate‐determining step, achieving the lowest theoretical overpotential.

Strategically designing and fabricating nitrogen and sulfur Co-doped g-C3N4 for accelerating photocatalytic H2 evolution

Doping engineering is an effective strategy for graphitic carbon nitride (g-C3N4) to improve its photocatalytic hydrogen evolution reaction (HER) performance. In this work, a novel nitrogen and sulfur co-doped g-C3N4 (N, S-g-C3N4) is elaborately designed on the basis of theoretical predictions of first-principle density functional theory (DFT). The calculated Gibbs free energy of adsorbed hydrogen (ΔGH*) for N, S-g-C3N4 at the N-doping active sites is extremely close to zero (0.01 eV). Inspired by the theoretical predictions, the N, S-g-C3N4 is successfully fabricated through ammonia-rich pyrolysis synthesis strategy, in which ammonia is in-situ obtained by pyrolyzing melamine. Subsequent characterizations indicate that the N, S-g-C3N4 possesses high specific surface area, outstanding light utilization, good hydrophilicity, and efficient carrier transfer efficiency. Consequently, the N, S-g-C3N4 displays an extremely high H2 evolution rate of 8269.9 µmol g−1 h−1, achieves an apparent quantum efficiency (AQE) of 3.24%, and also possesses outsatnding durability. Theoretical calculations further demonstrate that N and S dopants can not only introduce doping energy level to reduce the band gap, but also induce charge redistribution to facilitate hydrogen adsorption, thus promoting the photocatalytic HER process. Moreover, femtosecond transient absorption (fs-TA) spectroscopy further corroborates the efficient photogenerated carrier transport of N, S-g-C3N4. This research highlights a promising and reliable strategy to achieve superior photocatalytic activity, and exhibits significant guidance for precise designing high-efficiency photocatalysts.

Rational design of multi-component Fe(OH)3/Ni-NiO heterostructures bifunctional catalyst for electrochemical water splitting

Exploring economic-efficient bifunctional catalysts is critical for the production of green hydrogen through water splitting. Herein, we fabricate a novel hybrid catalyst with three-phase heterojunction (Fe(OH)3/Ni-NiO) via a simple electrodeposition and chemical precipitation method. Benefiting from the desirable amorphous-crystal interfaces, the electronic structure of Ni, NiO and Fe(OH)3 is regulated, which will optimize the adsorption of H intermediates (H*) and also reduce the kinetic barrier for the hydrogen evolution reaction (HER). The optimal Fe(OH)3–3/Ni-NiO/CC shows superior bifunctional activity with low overpotentials of 66 mV for HER and 220 mV for OER at 10 mA cm−2 in alkaline solution, respectively, as well as remarkable durability over a period of 40 h. Besides, Fe(OH)3–3/Ni-NiO/CC requires 1.52 and 1.72 V to deliver 10 and 100 mA cm−2 and shows no obvious increase in current within 40 h toward overall water splitting. Experimental and theoretical results show that the HER process is promoted by the synergistic effect of electronic redistribution between Ni, NiO and Fe(OH)3 due to the construction of three phase crystalline-amorphous heterogeneous interface. Meanwhile, Fe(OH)3 and NiO appeared reconstruction, transforming into FeOOH and NiOOH during OER process, respectively. This work offers a simple synthesis method for designing bifunctional catalysts for water splitting.

Molybdenum-doped tungsten nitride coated with carbon shell and cobalt hydroxide nanosheets for efficient alkaline hydrogen evolution reaction

Water electrolysis is currently the most important way to achieve large-scale hydrogen (H2) production. Although many nonprecious electrocatalysts possess promising catalytic performance at low current density below 50 mA cm−2, it remains a substantial challenge to realize H2 production at industry-compatible current density over 500 mA cm−2. Here we have designed a hierarchical heterostructure of molybdenum-doped tungsten nitride coated with carbon shell and cobalt hydroxide nanosheets (Mo-WN@NC@Co(OH)2) for alkaline hydrogen evolution reaction (HER) with industrial current density and stability. The hybrid exhibits efficient alkaline HER activity, reaching the current density of 500 mA cm−2 at an overpotential of 196 mV. The Co(OH)2 nanosheets and Mo doping endow the composite with more active sites and enhanced intrinsic activity of the catalyst, as well as an appropriate water dissociation energy. In addition, the free energy of activation for each step during the HER process suggests a synergistic effect of Mo doping and Co(OH)2 in Mo-WN@NC@Co(OH)2 promoting surface Volmer and Heyrovsky steps during the HER process. This doping and interfacial engineering methods hold great promise for fabricating efficient nitride-based electrocatalysts for electrochemical energy devices.

Biologically templated formation of Cobalt-Phosphide-Graphene hybrids with charge redistribution for efficient hydrogen evolution

Developing highly efficient and sustainable hydrogen evolution reaction (HER) electrocatalysts is important for the practical application of emerging energy technologies. The spherical structure and phosphorus-rich properties of Chlorella can facilitate the construction of comparable transition metal phosphide electrocatalysts. Here, a microorganism template strategy is proposed to construct a cobalt-phosphide-graphene hybrid. Chlorella can absorb metal ions, and the generated rough spherical nanoparticles are uniformly distributed around the reduced graphene oxide nanosheets. This designed catalyst has comparable HER performance in acidic electrolytes and needs an overpotential of only 153 mV at a current density of 10 mA cm−2. The experimental and density functional theory results imply that the charge redistribution between Co2P and pyrrole-N is the key factor in enhancing the HER activity. The induced electron aggregation at the N and P sites can serve as a key active site for absorbing the adsorbed hydrogen atom intermediate to accelerate the HER process, contributing to the active sites of Co2P- and pyrrole-N-doped carbon with 0 eV hydrogen adsorption free energy. This work provides a broad idea for synthesizing advanced catalysts by a biological template approach, facilitating the innovative integration of biology and emerging electrochemical energy technologies.

Experimental optimization of the sono-photocatalytic hydrogen evolution reaction (HER) using 1D ZnO and cobalt phthalocyanine

This study presents the sono-photocatalytic hydrogen generation (HER), using ZnO and theraphthal, a water-soluble sodium salt of cobalt 4,5-carboxyphthalocyanine (TP). HER efficiency was optimized by a multivariable design of experiments modifying 5 factors (additives): (i) ascorbic acid, (ii) zinc oxide load, (iii) ultrasound power, (iv) ethanol, and (v) theraphthal under UV irradiation. Differences in hydrogen production according to the variable employed factors were observed in the reactions, resulting in higher yields when larger amounts of ethanol were used. Hydrogen evolution reached a maximum concentration near to 67 μmol (669 μmol g−1) in the HER process, when zinc oxide, theraphthal, and ascorbic acid in water/ethanol mixture were combined. Statistical analysis suggests that the H2 production was influenced mainly by the presence of alcohol in the reaction medium.

Synchronously integration of carbon-quantum-dot and Cu, Mo dual-metal doped in Ni3S2@Ni foam toward robust and stable electrocatalytic hydrogen generation

In the pursuit of advancing the production of H2 through hydrogen-evolution reaction (HER), the demand for the elaborate design of cost-effective and robust durability electrocatalysts has gained momentum, especially replacement of noble-metal counterparts like Pt. Herein, we introduce a facile one-pot hydrothermal approach to synthesize nickel foam-supported Ni3S2 nanosheet arrays, which integrate with carbon-quantum-dot (CQDs) and Cu, Mo dual-metal doped. With the introduction of CQDs and Cu, Mo dual-metal doped site, the optimal CQDs-Cu-Mo-Ni3S2@NF exhibits superior HER catalytic activity with a low overpotential of 125 mV at 10 mA cm-2 and strong durability for 30 h in alkaline medium. The exceptional electrocatalytic performance is ascribed to the synergistic effect of CQDs and Cu, Mo dual-metal site. This synergy encompasses optimization of water molecule adsorption/desorption energetics, elevated electrical conductivity, weakening of the strong S-H bond interaction on the Ni3S2 surface, and providing ample active centers. Furthermore, an in-depth understanding of the electronic structure and adsorption energy during the HER process is probed by density functional theory (DFT) analysis. Our work provides a quintessential paradigm for the rational design of multi-component electrocatalysts for water splitting.

In Situ Probing the Structure Change and Interaction of Interfacial Water and Hydroxyl Intermediates on Ni(OH)2 Surface over Water Splitting.

There is growing acknowledgment that the properties of the electrochemical interfaces play an increasingly pivotal role in improving the performance of the hydrogen evolution reaction (HER). Here, we present, for the first time, direct dynamic spectral evidence illustrating the impact of the interaction between interfacial water molecules and adsorbed hydroxyl species (OHad) on the HER properties of Ni(OH)2 using Au/core-Ni(OH)2/shell nanoparticle-enhanced Raman spectroscopy. Notably, our findings highlight that the interaction between OHad and interfacial water molecules promotes the formation of weakly hydrogen-bonded water, fostering an environment conducive to improving the HER performance. Furthermore, the participation of OHad in the reaction is substantiated by the observed deprotonation step of Au@2 nm Ni(OH)2 during the HER process. This phenomenon is corroborated by the phase transition of Ni(OH)2 to NiO, as verified through Raman and X-ray photoelectron spectroscopy. The significant redshift in the OH-stretching frequency of water molecules during the phase transition confirms that surface OHad disrupts the hydrogen-bond network of interfacial water molecules. Through manipulation of the shell thickness of Au@Ni(OH)2, we additionally validate the interaction between OHad and interfacial water molecules. In summary, our insights emphasize the potential of electrochemical interfacial engineering as a potent approach to enhance electrocatalytic performance.

Three-dimensional Co–MoS2/Ni3S2/Ni assembly with interfacial engineering and electronic modulation for efficient hydrogen evolution reaction

To maximize the active sites and accelerate the electron transfer are of significant importance for developing efficient MoS2-based catalysts towards hydrogen evolution reaction (HER). Herein, we report a facile one-step construction of three-dimensional assembly in which Co doped MoS2 nanoflowers are attached on partially sulfided nickel foam (Co–MoS2/Ni3S2/Ni). The three-dimensional structure enables maximum exposure of the active sites. Besides, interfacial interaction between MoS2 and Ni3S2 accelerates the electron transfer kinetics and increases the electrochemically active surface area. Additionally, electronic synergy effect of Co to MoS2 promotes the formation of 1T-MoS2 phase. Consequently, the optimized Co–MoS2/Ni3S2/Ni catalyst shows a superior HER performance with low overpotentials of 43 mV and 201 mV to achieve the current densities of 10 mA/cm2 and 100 mA/cm2, as well as an excellent stability of 11 h. Besides, Co–MoS2/Ni3S2/Ni has a small Tafel slope of 53 mV dec−1 which indicates a combined Volmer-Heyrovsky mechanism during the HER process. This work provides a novel insight for designing excellent MoS2-based HER catalysts through electronic modulation and interfacial engineering.

Highly Uniform Nanodiamond-Graphene Composites Microspheres for Electrocatalytic Hydrogen Evolution.

To progress the clean hydrogen-gas-based energy economy, there is a demand for cost-effective, highly efficient catalysts to facilitate the hydrogen evolution reaction process (HER). Due to the amazing catalytic capabilities of two-dimensional materials, extensive research has been done on these structures. However, most of the described syntheses take a lot of time, are challenging, and are ineffective. The present work demonstrates the performance of the recently reported nanodiamond/graphene composite microsphere ND-GCSs as a catalyst for HER. These spheres were produced via the microwave-irradiation approach. A modified process was adopted to improve the particle size uniformity and yield. The prepared composite spheres showed very interesting catalytic activity for the HER when assembled on a screen-printed carbon electrode. The prepared ND-GCSs@SPCE showed a significant shift of the onset potential to ca. -450 mV and a small Tafel slope value of ca. 85 mV/decade. The electron transfer was drastically enhanced with a tremendous decrease in charge transfer resistance to ca. 265 Ω. The electrocatalyst showed excellent long-term stability for the HER application. Additionally, this novel composite structure might be beneficial for diverse applications including batteries, supercapacitors, catalyst supports, and more.

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.

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.

Aqueous pH influence on the electrocatalytic hydrogen evolution reaction with carbon nanotube-supported diiron dithiolato compound

Biomimetic chemistry on structure, function and external environment of [FeFe]-hydrogenases for hydrogen evolution reaction (HER) has shown a promising way to develop non-precious metal electrocatalysts for H2 production in the current Pt-dominated HER system. Herein, three new diiron dithiolato compounds [{(μ-SCH2)2N(C6H4CH2CO2R)}Fe2(CO)6] (R = H (1), C6H4CHO-p (2), and C6H4Me-m (3)) were first prepared and identified as a library of [FeFe]-hydrogenase models in this work. Subsequently, the as-prepared diiron molecule 2 can be covalently attached onto carbon nanotubes (CNTs), resulting in the obtainment of target CNT-supported [FeFe]-hydrogenase model labeling as covalent hybrid 2Fe2S-f-CNT. Notably, the electrocatalytic HER performance and stability of the resulted hybrid 2Fe2S-f-CNT immobilized respectively on a gassy carbon (GC) electrode are systematically studied and compared in 0.1 M KOH (pH = 13), 0.1 M phosphate buffer (pH = 7), and 0.05 M H2SO4 (pH = 1) aqueous solutions by various spectroscopic and electrochemical techniques. The result has shown that the higher electrocatalytic HER activity is observed in alkaline solution (pH = 13) relative to neutral and acidic solutions (pH = 7, 1), being attributed to the different electrochemical HER processes of diiron cluster in wide pH aqueous media as revealed by post operando analysis.

Interfacial Design of Ti3C2Tx MXene/Graphene Heterostructures Boosted Ru Nanoclusters with High Activity Toward Hydrogen Evolution Reaction.

The development of a cost-competitive and efficient electrocatalyst is both attractive and challenging for hydrogen production by hydrogen evolution reaction (HER). Herein, a facile glycol reduction method to construct Ru nanoclusters coupled with hierarchical exfoliated-MXene/reduced graphene oxide architectures (Ru-E-MXene/rGA) is reported. The hierarchical structure, formed by the self-assembly of graphene oxides, can effectively prohibit the self-stacking of MXene nanosheets. Meanwhile, the formation of the MXene/rGA interface can strongly trap the Ru3+ ions, resulting in the uniform distribution of Ru nanoclusters within Ru-E-MXene/rGA. The boosted catalytic activity and underlying catalytic mechanism during the HER process are proved by density functional theory. Ru-E-MXene/rGA exhibits overpotentials of 42 and 62mV at 10mAcm-2 in alkaline and acidic electrolytes, respectively. The small Tafel slope and charge transfer resistance (Rct) values elucidate its fast dynamic behavior. The cyclic voltammetry (CV) curves and chronoamperometry test confirm the high stability of Ru-E-MXene/rGA. These results demonstrate that coupling Ru nanoclusters with the MXene/rGA heterostructure represents an efficient strategy for constructing MXene-based catalysts with enhanced HER activity.

Substantial Impact of Built-in Electric Field and Electrode Potential on the Alkaline Hydrogen Evolution Reaction of Ru-CoP Urchin Arrays.

Although great efforts on the delicate construction of a built-in electric field (BIEF) to modify the electronic properties of active sites have been conducted, the substantial impact of BIEF coupled with electrode potential on the electrochemical reactions has not been clearly investigated. Herein, we designed an alkaline hydrogen evolution reaction (HER) catalyst composed of heterogeneous Ru-CoP urchin arrays on carbon cloth (Ru-CoP/CC) with a strong BIEF with the guidance of density functional theory (DFT) calculations. Impressively, despite its unsatisfactory activity at 10 mA cm-2 (overpotential of 44 mV), Ru-CoP/CC exhibited better activity (357 mV) than the benchmark Pt/C catalyst (505 mV) at 1 A cm-2 . Experimental and theoretical studies revealed that strong hydrogen adsorption on the interfacial Ru atoms created a high energy barrier for hydrogen desorption and spillover, resulting in unsatisfactory activity at low current densities. However, as the electrode potential became more negative (i.e., the current density increased), the barrier for hydrogen spillover from the interfacial Ru to the Co site, which had near-zero hydrogen adsorption energy, significantly decreased, thus greatly accelerating the whole alkaline HER process. This explains why the activity of Ru-CoP is relatively susceptible to the electrode potential compared to Pt/C.

Effect of molybdenum doping Zn-Co spinel oxide microspheres for efficient electrocatalytic hydrogen production in alkaline media and study supported by DFT

The rational design of efficient transition metal-based electrocatalysts for the hydrogen evolution reaction (HER) is critical for the water-splitting process. Industrial water-alkali electrolysis requires large current densities at low overpotentials, which are always limited by the intrinsic activity. Here, ZnCo2−xMoxO4 (x ≤ 0.10) spinel oxide microsphere electrocatalysts were synthesized for the process in alkaline media. Mo doping in the ZnCo2O4 crystal structure enhanced the active sites, which were responsible for the enhancement in the HER process. The ZnCo2−xMoxO4 (x = 0.06) electrocatalyst exhibited exceptional HER activity, as evidenced by an overpotential of 195 mV, Tafel slope of 81.4 mVs−1 and high stability for 40 h with 1000 cycles linear sweep voltammetry. The surface and electrochemical characterization revealed that 6% Mo-doping exhibits improved the HER activity due to a significantly higher electrochemical surface area and accelerated charge transfer kinetics at the semiconductor electrolyte interface. Density functional theory (DFT) for exploring and explaining the effect of the Mo dopants on the HER activity elucidated that hydrogen and water molecules are adsorbed on the surface of the Mo-doped ZnCo2O4 slab structures. The results show that Mo dopants enhance the chemical activity, due to water adsorption, and HER activity for enhanced electrocatalytic processes. This work provides a new insight into low-metal-cost materials for efficient and durable HER electrocatalysts and successfully showcases the catalyst model for a detailed mechanistic insight into the HER process.

Ir nanoclusters on ZIF-8-derived nitrogen-doped carbon frameworks to give a highly efficient hydrogen evolution reaction

The precise change of the electronic structure of active metals using low-active supports is an effective way of developing high-performance electrocatalysts. The electronic interaction of the metal and support provides a flexible way of optimizing the catalytic performance. We have fabricated an efficient hydrogen evolution reaction (HER) electrocatalyst, in which Ir nanoclusters are uniformly loaded on a nitrogen-doped carbon framework (Ir@NC). The synthesis process entails immersing an annealed zeolitic imidazolate framework-8 (ZIF-8), prepared at 900 °C as a carbon source, into an IrCl3 solution, followed by a calcination-reduction treatment at 400 °C under a H2/Ar atmosphere. The three-dimensional porous structure of the nitrogen-doped carbon framework exposes more active metal sites, and the combined effect of the Ir clusters and the N-doped carbon support efficiently changes the electronic structure of Ir, optimizing the HER process. In acidic media, Ir@NC has a remarkable HER electrocatalytic activity, with an overpotential of only 23 mV at 10 mA cm−2, an ultra-low Tafel slope (25.8 mV dec−1) and good stability for over 24 h at 10 mA cm−2. The high activity of the electrocatalyst with a simple and scalable synthesis method makes it a highly promising candidate for the industrial production of hydrogen by splitting acidic water.