Holey Reduced Graphene Oxide Coupled with an Mo2N–Mo2C Heterojunction for Efficient Hydrogen Evolution

An in situ catalytic etching strategy is developed to fabricate holey reduced graphene oxide along with simultaneous coupling with a small‐sized Mo₂N–Mo₂C heterojunction (Mo₂N–Mo₂C/HGr). The method includes the first immobilization of H₃PMo₁₂O₄₀ (PMo₁₂) clusters on graphite oxide (GO), followed by calcination in air and NH₃ to form Mo₂N–Mo₂C/HGr. PMo₁₂ not only acts as the Mo heterojunction source, but also provides the Mo species that can in situ catalyze the decomposition of adjacent reduced GO to form HGr, while the released gas (CO) and introduced NH₃ simultaneously react with the Mo species to form an Mo₂N–Mo₂C heterojunction on HGr. The hybrid exhibits superior activity towards the hydrogen evolution reaction with low onset potentials of 11 mV (0.5 m H₂SO₄) and 18 mV (1 m KOH) as well as remarkable stability. The activity in alkaline media is also superior to Pt/C at large current densities (>88 mA cm^?2). The good activity of Mo₂N–Mo₂C/HGr is ascribed to its small size, the heterojunction of Mo₂N–Mo₂C, and the good charge/mass‐transfer ability of HGr, as supported by a series of experiments and theoretical calculations.     

Edge‐Riched MoSe2/MoO2 Hybrid Electrocatalyst for Efficient Hydrogen Evolution Reaction

Molybdenum diselenide (MoSe₂) is widely considered as one of the most promising catalysts for the hydrogen evolution reaction (HER). However, the absence of active sites and poor conductivity of MoSe₂ severely restrict its HER performance. By introducing a layer of MoO₂ on Mo foil, MoSe₂/MoO₂ hybrid nanosheets with an abundant edge and high electrical conductivity can be synthesized on the surface of Mo foil. Metallic MoO₂ can improve the charge transport efficiency of MoSe₂/MoO₂, thereby enhancing the overall HER performance. MoSe₂/MoO₂ exhibits fast hydrogen evolution kinetics with a small overpotential of 142 mV versus RHE at a current density of 10 mA cm^?2 and Tafel slope of 48.9 mV dec^?1.     

Formation of Mo–Polydopamine Hollow Spheres and Their Conversions to MoO2/C and Mo2C/C for Efficient Electrochemical Energy Storage and Catalyst

Highly uniform hierarchical Mo–polydopamine hollow spheres are synthesized for the first time through a liquid‐phase reaction under ambient temperature. A self‐assembly mechanism of the hollow structure of Mo–polydopamine precursor is discussed in detail, and a determined theory is proposed in a water‐in‐oil system. Via different annealing process, these precursors can be converted into hierarchical hollow MoO₂/C and Mo₂C/C composites without any distortion in shape. Owing to the well‐organized structure and nanosize particle embedding, the as‐prepared hollow spheres exhibit appealing performance both as the anode material for lithium‐ion batteries and as the catalyst for hydrogen evolution reaction (HER). Accordingly, MoO₂/C delivers a high reversible capacity of 940 mAh g^?1 at 0.1 A g^?1 and 775 mAh g^?1 at 1 A g^?1 with good rate capability and long cycle performance. Moreover, Mo₂C/C also exhibits an enhanced electrocatalytic performance with a low overpotential for HER in both acidic and alkaline conditions, as well as remarkable stability.     

Directional Construction of Vertical Nitrogen‐Doped 1T‐2H MoSe2/Graphene Shell/Core Nanoflake Arrays for Efficient Hydrogen Evolution Reaction

The low utilization of active sites and sluggish reaction kinetics of MoSe₂ severely impede its commercial application as electrocatalyst for hydrogen evolution reaction (HER). To address these two issues, the first example of introducing 1T MoSe₂ and N dopant into vertical 2H MoSe₂/graphene shell/core nanoflake arrays that remarkably boost their HER activity is herein described. By means of the improved conductivity, rich catalytic active sites and highly accessible surface area as a result of the introduction of 1T MoSe₂ and N doping as well as the unique structural features, the N‐doped 1T‐2H MoSe₂/graphene (N‐MoSe₂/VG) shell/core nanoflake arrays show substantially enhanced HER activity. Remarkably, the N‐MoSe₂/VG nanoflakes exhibit a relatively low onset potential of 45 mV and overpotential of 98 mV (vs RHE) at 10 mA cm^?2 with excellent long‐term stability (no decay after 20 000 cycles), outperforming most of the recently reported Mo‐based electrocatalysts. The success of improving the electrochemical performance via the introduction of 1T phase and N dopant offers new opportunities in the development of high‐performance MoSe₂‐based electrodes for other energy‐related applications.     

Graphene Nanoarchitectonics: Recent Advances in Graphene‐Based Electrocatalysts for Hydrogen Evolution Reaction

Under the double pressures of both the energy crisis and environmental pollution, the exploitation and utilization of hydrogen, a clean and renewable power resource, has become an important trend in the development of sustainable energy‐production and energy‐consumption systems. In this regard, the electrocatalytic hydrogen evolution reaction (HER) provides an efficient and clean pathway for the mass production of hydrogen fuel and has motivated the design and construction of highly active HER electrocatalysts of an acceptable cost. In particular, graphene‐based electrocatalysts commonly exhibit an enhanced HER performance owing to their distinctive structural merits, including a large surface area, high electrical conductivity, and good chemical stability. Considering the rapidly growing research enthusiasm for this topic over the last several years, herein, a panoramic review of recent advances in graphene‐based electrocatalysts is presented, covering various advanced synthetic strategies, microstructural characterizations, and the applications of such materials in HER electrocatalysis. Lastly, future perspectives on the challenges and opportunities awaiting this emerging field are proposed and discussed.     

Nickel@Nitrogen‐Doped Carbon@MoS2 Nanosheets: An Efficient Electrocatalyst for Hydrogen Evolution Reaction

Developing cheap, abundant, and easily available electrocatalysts to drive the hydrogen evolution reaction (HER) at small overpotentials is an urgent demand of hydrogen production from water splitting. Molybdenum disulfide (MoS₂) based composites have emerged as competitive electrocatalysts for HER in recent years. Herein, nickel@nitrogen‐doped carbon@MoS₂ nanosheets (Ni@NC@MoS₂) hybrid sub‐microspheres are presented as HER catalyst. MoS₂ nanosheets with expanded interlayer spacings are vertically grown on nickel@nitrogen‐doped carbon (Ni@NC) substrate to form Ni@NC@MoS₂ hierarchical sub‐microspheres by a simple hydrothermal process. The formed Ni@NC@MoS₂ composites display excellent electrocatalytic activity for HER with an onset overpotential of 18 mV, a low overpotential of 82 mV at 10 mA cm^?2, a small Tafel slope of 47.5 mV dec^?1, and high durability in 0.5 H₂SO₄ solution. The outstanding HER performance of the Ni@NC@MoS₂ catalyst can be ascribed to the synergistic effect of dense catalytic sites on MoS₂ nanosheets with exposed edges and expanded interlayer spacings, and the rapid electron transfer from Ni@NC substrate to MoS₂ nanosheets. The excellent Ni@NC@MoS₂ electrocatalyst promises potential application in practical hydrogen production, and the strategy reported here can also be extended to grow MoS₂ on other nitrogen‐doped carbon encapsulated metal species for various applications.     

Molybdenum Sulphoselenophosphide Spheroids as an Effective Catalyst for Hydrogen Evolution Reaction

Electrocatalytic splitting of water is the most convincing and straight forward path to extract hydrogen, but the efficiency of this process relies heavily on the catalyst employed. Here, molybdenum sulphoselenophosphide (MoS_45.1Se_11.7P_6.1) spheroids are reported as an active catalyst for the hydrogen evolution reaction (HER) and this is the first attempt to study on ternary anion based molybdenum chalcogenides. As‐prepared MoS_xSe_yP_z catalyst reveals a unique morphology of microspheroids capped by stretched‐out nanoflakes that exhibits excellent electrocatalytic activity ( j—10 mA cm^?2 @ 93 mV, Tafel slope of 50.1 mV dec^?1, TOF—0.40 s^?1) fairly closer to the performance of platinum (Pt) and predominant to those of the pre‐existing Mo‐chalcogenides and phosphides. Such an increase in performance stems from the copious amount of active edge sites, the presence of nanoflakes, and high circumferential area exposed by the spheroids. Besides, the electrode with MoS_45.1Se_11.7P_6.1 displays excellent stability in acidic medium over 10 h of continuous operation. This work paves way for improving the catalytic activity of existing Mo‐chalcogenide compounds by doping suitable mixed anions and also reveals the integral role of anions as well as their synergetic effects on the surface physiochemical properties and the HER catalysis.     

Urchin-Like Structured MoO2/Mo3P/Mo2C Triple-Interface Heterojunction Encapsulated within Nitrogen-Doped Carbon for Enhanced Hydrogen Evolution Reaction

The development of highly efficient and cost-effective hydrogen evolution reaction (HER) catalysts is highly desirable to efficiently promote the HER process, especially under alkaline condition. Herein, a polyoxometalates-organic-complex-induced carbonization method is developed to construct MoO₂/Mo₃P/Mo₂C triple-interface heterojunction encapsulated into nitrogen-doped carbon with urchin-like structure using ammonium phosphomolybdate and dopamine. Furthermore, the mass ratio of dopamine and ammonium phosphomolybdate is found critical for the successful formation of such triple-interface heterojunction. Theoretical calculation results demonstrate that such triple-interface heterojunctions possess thermodynamically favorable water dissociation Gibbs free energy (ΔG_H2O) of -1.28 eV and hydrogen adsorption Gibbs free energy (ΔG_H*) of -0.41 eV due to the synergistic effect of Mo₂C and Mo₃P as water dissociation site and H* adsorption/desorption sites during the HER process in comparison to the corresponding single components. Notably, the optimal heterostructures exhibit the highest HER activity with the low overpotential of 69 mV at the current density of 10 mA cm⁻² and a small Tafel slope of 60.4 mV dec⁻¹ as well as good long-term stability for 125 h. Such remarkable results have been theoretically and experimentally proven to be due to the synergistic effect between the unique heterostructures and the encapsulated nitrogen-doped carbon.     

Combining Highly Dispersed Amorphous MoS3 with Pt Nanodendrites as Robust Electrocatalysts for Hydrogen Evolution Reaction

Surface modification of electrocatalysts to obtain new or improved electrocatalytic performance is currently the main strategy for designing advanced nanocatalysts. In this work, highly dispersed amorphous molybdenum trisulfide-anchored Platinum nanodendrites (denoted as Pt-a-MoS₃ NDs) are developed as efficient hydrogen evolution electrocatalysts. The formation mechanism of spontaneous in situ polymerization MoS₄²⁻ into a-MoS₃ on Pt surface is discussed in detail. It is verified that the highly dispersed a-MoS₃ enhances the electrocatalytic activity of Pt catalysts under both acidic and alkaline conditions. The potentials at the current density of 10 mA cm⁻² (η₁₀) in 0.5 m  sulfuric acid (H₂SO₄) and 1 m  potassium hydroxide (KOH) electrolyte are −11.5 and −16.3 mV, respectively, which is significantly lower than that of commercial Pt/C (−20.2 mV and −30.7 mV). This study demonstrates that such high activity benefits from the interface between highly dispersed a-MoS₃ and Pt sites, which act as the preferred adsorption sites for the efficient conversion of hydrion (H⁺) to hydrogen (H₂). Additionally, the anchoring of highly dispersed clusters to Pt substrate greatly enhances the corresponding electrocatalytic stability.     

Interstitial Hydrogen Atom to Boost Intrinsic Catalytic Activity of Tungsten Oxide for Hydrogen Evolution Reaction

Tungsten oxide (WO₃) is an appealing electrocatalyst for the hydrogen evolution reaction (HER) owing to its cost-effectiveness and structural adjustability. However, the WO₃ electrocatalyst displays undesirable intrinsic activity for the HER, which originates from the strong hydrogen adsorption energy. Herein, for effective defect engineering, a hydrogen atom inserted into the interstitial lattice site of tungsten oxide (H_0.23WO₃) is proposed to enhance the catalytic activity by adjusting the surface electronic structure and weakening the hydrogen adsorption energy. Experimentally, the H_0.23WO₃ electrocatalyst is successfully prepared on reduced graphene oxide. It exhibits significantly improved electrocatalytic activity for HER, with a low overpotential of 33 mV to drive a current density of 10 mA cm⁻² and ultra-long catalytic stability at high-throughput hydrogen output (200 000 s, 90 mA cm⁻²) in acidic media. Theoretically, density functional theory calculations indicate that strong interactions between interstitial hydrogen and lattice oxygen lower the electron density distributions of the d-orbitals of the active tungsten (W) centers to weaken the adsorption of hydrogen intermediates on W-sites, thereby sufficiently promoting fast desorption from the catalyst surface. This work enriches defect engineering to modulate the electron structure and provides a new pathway for the rational design of efficient catalysts for HER.     

Molybdenum Carbide‐Decorated Metallic Cobalt@Nitrogen‐Doped Carbon Polyhedrons for Enhanced Electrocatalytic Hydrogen Evolution

Electrocatalytic hydrogen evolution reaction (HER) based on water splitting holds great promise for clean energy technologies, in which the key issue is exploring cost‐effective materials to replace noble metal catalysts. Here, a sequential chemical etching and pyrolysis strategy are developed to prepare molybdenum carbide‐decorated metallic cobalt@nitrogen‐doped porous carbon polyhedrons (denoted as Mo/Co@N–C) hybrids for enhanced electrocatalytic hydrogen evolution. The obtained metallic Co nanoparticles are coated by N‐doped carbon thin layers while the formed molybdenum carbide nanoparticles are well‐dispersed in the whole Co@N–C frames. Benefiting from the additionally implanted molybdenum carbide active sites, the HER performance of Mo/Co@N–C hybrids is significantly promoted compared with the single Co@N–C that is derived from the pristine ZIF‐67 both in alkaline and acidic media. As a result, the as‐synthesized Mo/Co@N–C hybrids exhibit superior HER electrocatalytic activity, and only very low overpotentials of 157 and 187 mV are needed at 10 mA cm^?2 in 1 m KOH and 0.5 m H₂SO₄, respectively, opening a door for rational design and fabrication of novel low‐cost electrocatalysts with hierarchical structures toward electrochemical energy storage and conversion.     

Structurally Deformed MoS2 for Electrochemically Stable,Thermally Resistant,and Highly Efficient Hydrogen Evolution Reaction

The emerging molybdenum disulfide (MoS₂) offers intriguing possibilities for realizing a transformative new catalyst for driving the hydrogen evolution reaction (HER). However, the trade‐off between catalytic activity and long‐term stability represents a formidable challenge and has not been extensively addressed. This study reports that metastable and temperature‐sensitive chemically exfoliated MoS₂ (ce‐MoS₂) can be made into electrochemically stable (5000 cycles), and thermally robust (300 °C) while maintaining synthetic scalability and excellent catalytic activity through physical‐transformation into 3D structurally deformed nanostructures. The dimensional transition enabled by a high throughput electrohydrodynamic process provides highly accessible, and electrochemically active surface area and facilitates efficient transport across various interfaces. Meanwhile, the hierarchically strained morphology is found to improve electronic coupling between active sites and current collecting substrates without the need for selective engineering the electronically heterogeneous interfaces. Specifically, the synergistic combination of high strain load stemmed from capillarity‐induced‐self‐crumpling and sulfur (S) vacancies intrinsic to chemical exfoliation enables simultaneous modulation of active site density and intrinsic HER activity regardless of continuous operation or elevated temperature. These results provide new insights into how catalytic activity, electrochemical‐, and thermal stability can be concurrently enhanced through the physical transformation that is reminiscent of nature, in which properties of biological materials emerge from evolved dimensional transitions.     

Ultrafine Co Nanoparticles Encapsulated in Carbon‐Nanotubes‐Grafted Graphene Sheets as Advanced Electrocatalysts for the Hydrogen Evolution Reaction

The rational design of an efficient and inexpensive electrocatalyst based on earth‐abundant 3d transition metals (TMs) for the hydrogen evolution reaction still remains a significant challenge in the renewable energy area. Herein, a novel and effective approach is developed for synthesizing ultrafine Co nanoparticles encapsulated in nitrogen‐doped carbon nanotubes (N‐CNTs) grafted onto both sides of reduced graphene oxide (rGO) (Co@N‐CNTs@rGO) by direct annealing of GO‐wrapped core–shell bimetallic zeolite imidazolate frameworks. Benefiting from the uniform distribution of Co nanoparticles, the in‐situ‐formed highly graphitic N‐CNTs@rGO, the large surface area, and the abundant porosity, the as‐fabricated Co@N‐CNTs@rGO composites exhibit excellent electrocatalytic hydrogen evolution reaction (HER) activity. As demonstrated in electrochemical measurements, the composites can achieve 10 mA cm^?2 at low overpotential with only 108 and 87 mV in 1 m KOH and 0.5 m H₂SO₄, respectively, much better than most of the reported Co‐based electrocatalysts over a wide pH range. More importantly, the synthetic strategy is versatile and can be extended to prepare other binary or even ternary TMs@N‐CNTs@rGO (e.g., Co–Fe@N‐CNTs@rGO and Co–Ni–Cu@N‐CNTs@rGO). The strategy developed here may open a new avenue toward the development of nonprecious high‐performance HER catalysts.     

Metal–Carbon Hybrid Electrocatalysts Derived from Ion‐Exchange Resin Containing Heavy Metals for Efficient Hydrogen Evolution Reaction

Transition metal–carbon hybrids have been proposed as efficient electrocatalysts for hydrogen evolution reaction (HER) in acidic media. Herein, effective HER electrocatalysts based on metal–carbon composites are prepared by controlled pyrolysis of resin containing a variety of heavy metals. For the first time, Cr₂O₃ nanoparticles of 3–6 nm in diameter homogeneously dispersed in the resulting porous carbon framework (Cr–C hybrid) is synthesized as efficient HER electrocatalyst. Electrochemical measurements show that Cr–C hybrids display a high HER activity with an onset potential of ?49 mV (vs reversible hydrogen electrode), a Tafel slope of 90 mV dec^?1, a large catalytic current density of 10 mA cm^?2 at ?123 mV, and the prominent electrochemical durability. X‐ray photoelectron spectroscopic measurements confirm that electron transfer occurs from Cr₂O₃ into carbon, which is consistent with the reported metal@carbon systems. The obtained correlation between metals and HER activities may be exploited as a rational guideline in the design and engineering of HER electrocatalysts.     

Ultrasmall MoOx Clusters as a Novel Cocatalyst for Photocatalytic Hydrogen Evolution

To enhance the performance of semiconductor photocatalysts, cocatalysts are used to accelerate surface reactions. Herein, ultrasmall molybdenum–oxygen (MoO_x) clusters are developed as a novel non‐noble cocatalyst, which significantly promotes the photocatalytic hydrogen generation rate of CdS nanowires (NWs). As indicated by extended X‐ray absorption fine structure analysis, direct bonds are formed between CdS NWs and MoO_x clusters, which guarantee the migration of photo‐generated charge carriers. Moreover, the MoO_x clusters induce deep electron trap states owing to the unique atomic arrangement and configuration with the generation of long‐lived electrons to enhance the activity. These findings may guide the design of efficient cocatalytic materials for solar water splitting and open a new avenue toward practical applications of ultrasmall clusters.