Wrinkled Rh2P Nanosheets as Superior pH‐Universal Electrocatalysts for Hydrogen Evolution Catalysis

Searching for highly efficient and durable electrocatalysts for the hydrogen evolution reaction (HER) that function effectively at all pHs is of great interest to the scientific community, however it is still a grand challenge, because the HER kinetics of Pt in alkaline solutions are approximately two to three orders of magnitude lower than that in acidic solution. Herein, a new class of wrinkled, ultrathin Rh₂P nanosheets for enhancing HER catalysis at all pHs is reported. They exhibit a small overpotential of 18.3 mV at 10 mA cm^?2, low Tafel slope of 61.5 mV dec^?1, and good durability in alkaline media, much better than the commercial Pt/C catalyst. Density functional theory calculations reveal that the active open‐shell effect from the P‐3p band not only promotes Rh‐4d for increased proton–electron charge exchange but also provides excellent p–p overlapping to locate the O‐related species as distributary center, which can benefit the HER process in alkaline media. It is also demonstrated that the present wrinkled, ultrathin Rh₂P nanosheets are highly efficient and durable electrocatalysts toward HER in both acid and neutral electrolytes. The present work opens a new material design for ultrathin 2D metal phosphide nanostructures for the purpose of boosting HER performance at all pHs.     

Ultrafine Pt Nanoparticle‐Decorated Pyrite‐Type CoS2 Nanosheet Arrays Coated on Carbon Cloth as a Bifunctional Electrode for Overall Water Splitting

To improve the utilization efficiency of precious metals, metal‐supported materials provide a direction for fabricating highly active and stable heterogeneous catalysts. Herein, carbon cloth (CC)‐supported Earth‐abundant CoS₂ nanosheet arrays (CoS₂/CC) are presented as ideal substrates for ultrafine Pt deposition (Pt‐CoS₂/CC) to achieve remarkable performance toward the hydrogen and oxygen evolution reactions (HER/OER) in alkaline solutions. Notably, the Pt‐CoS₂/CC hybrid delivers an overpotential of 24 mV at 10 mA cm^?2 and a mass activity of 3.89 A Pt_mg^?1, which is 4.7 times higher than that of commercial Pt/C, at an overpotential of 130 mV for catalyzing the HER. An alkali‐electrolyzer using Pt‐CoS₂/CC as a bifunctional electrode enables a water‐splitting current density of 10 mA cm^?2 at a low voltage of 1.55 V and can sustain for more than 20 h, which is superior to that of the state‐of‐the‐art Pt/C+RuO₂ catalyst. Further experimental and theoretical simulation studies demonstrate that strong electronic interaction between Pt and CoS₂ synergistically optimize hydrogen adsorption/desorption behaviors and facilitate the in situ generation of OER active species, enhancing the overall water‐splitting performance. This work highlights the regulation of interfacial and electronic synergy in pursuit of highly efficient and durable supported catalysts for hydrogen and oxygen electrocatalytic applications.     

Crystalline Ni(OH)2/Amorphous NiMoOx Mixed‐Catalyst with Pt‐Like Performance for Hydrogen Production

The achievement of effective alkaline hydrogen production from water electrolysis is an active field of research. Herein, an integrated electrode composed of crystalline Ni(OH)₂ and amorphous NiMoO_x is fabricated onto nickel foam (denoted as Ni(OH)₂–NiMoO_x/NF). The hydrogen evolution reaction (HER) kinetics are optimized along with phase transformation process during soaking operation. An overpotential of 36 mV to drive 10 mA cm^?2 along with the low Tafel slope of 38 mV dec^?1 reveals the catalyst's excellent HER performance and a Heyrovsky‐step‐controlled HER mechanism. When assembled into a urea‐assisted water electrolyzer, a voltage of 1.42 V can reach 10 mA cm^?2. Further experiments and Fourier transform infrared spectroscopy (FTIR) results illustrate the synergy effect between crystalline and amorphous areas and the optimized water dissociation step. Crystalline Ni(OH)₂ serves as the scissor for water dissociation in an alkali environment to produce H*, while the amorphous NiMoO_x layer serves as the location for H* adsorption and H₂ desorption.     

Earth‐Abundant Iron Diboride (FeB2) Nanoparticles as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting

Developing efficient, durable, and earth‐abundant electrocatalysts for both hydrogen and oxygen evolution reactions is important for realizing large‐scale water splitting. The authors report that FeB₂ nanoparticles, prepared by a facile chemical reduction of Fe²⁺ using LiBH₄ in an organic solvent, are a superb bifunctional electrocatalyst for overall water splitting. The FeB₂ electrode delivers a current density of 10 mA cm^?2 at overpotentials of 61 mV for hydrogen evolution reaction (HER) and 296 mV for oxygen evolution reaction (OER) in alkaline electrolyte with Tafel slopes of 87.5 and 52.4 mV dec^?1, respectively. The electrode can sustain the HER at an overpotential of 100 mV for 24 h and OER for 1000 cyclic voltammetry cycles with negligible degradation. Density function theory calculations demonstrate that the boron‐rich surface possesses appropriate binding energy for chemisorption and desorption of hydrogen‐containing intermediates, thus favoring the HER process. The excellent OER activity of FeB₂ is ascribed to the formation of a FeOOH/FeB₂ heterojunction during water oxidation. An alkaline electrolyzer is constructed using two identical FeB₂‐NF electrodes as both anode and cathode, which can achieve a current density of 10 mA cm^?2 at 1.57 V for overall water splitting with a faradaic efficiency of nearly 100%, rivalling the integrated state‐of‐the‐art Pt/C and RuO₂/C.     

Active Edge Sites Engineering in Nickel Cobalt Selenide Solid Solutions for Highly Efficient Hydrogen Evolution

An effective multifaceted strategy is demonstrated to increase active edge site concentration in Ni_0.33Co_0.67Se₂ solid solutions prepared by in situ selenization process of nickel cobalt precursor. The simultaneous control of surface, phase, and morphology result in as‐prepared ternary solid solution with extremely high electrochemically active surface area (C _dl = 197 mF cm^?2), suggesting significant exposure of active sites in this ternary compound. Coupled with metallic‐like electrical conductivity and lower free energy for atomic hydrogen adsorption in Ni_0.33Co_0.67Se₂, identified by temperature‐dependent conductivities and density functional theory calculations, the authors have achieved unprecedented fast hydrogen evolution kinetics, approaching that of Pt. Specifically, the Ni_0.33Co_0.67Se₂ solid solutions show a low overpotential of 65 mV at ?10 mV cm^?2, with onset potential of mere 18 mV, an impressive small Tafel slope of 35 mV dec^?1, and a large exchange current density of 184 µA cm^?2 in acidic electrolyte. Further, it is shown that the as‐prepared Ni_0.33Co_0.67Se₂ solid solution not only works very well in acidic electrolyte but also delivers exceptional hydrogen evolution reaction (HER) performance in alkaline media. The outstanding HER performance makes this solid solution a promising candidate for mass hydrogen production.     

Theoretical and Experimental Insight into the Effect of Nitrogen Doping on Hydrogen Evolution Activity of Ni3S2 in Alkaline Medium

Nickel sulfide (Ni₃S₂) is a promising hydrogen evolution reaction (HER) catalyst by virtue of its metallic electrical conductivity and excellent stability in alkaline medium. However, the reported catalytic activities for Ni₃S₂ are still relatively low. Herein, an effective strategy to boost the H adsorption capability and HER performance of Ni₃S₂ through nitrogen (N) doping is demonstrated. N‐doped Ni₃S₂ nanosheets achieve a fairly low overpotential of 155 mV at 10 mA cm^?2 and an excellent exchange current density of 0.42 mA cm^?2 in 1.0 m KOH electrolyte. The mass activity of 16.9 mA mg^?1 and turnover frequency of 2.4 s^?1 obtained at 155 mV are significantly higher than the values reported for other Ni₃S₂‐based HER catalysts, and comparable to the performance of best HER catalysts in alkaline medium. These experimental data together with theoretical analysis suggest that the outstanding catalytic activity of N‐doped Ni₃S₂ is due to the enriched active sites with favorable H adsorption free energy. The activity in the Ni₃S₂ is highly correlated with the coordination number of the surface S atoms and the charge depletion of neighbor Ni atoms. These new findings provide important guidance for future experimental design and synthesis of optimal HER catalysts.     

Copper–Nickel Nitride Nanosheets as Efficient Bifunctional Catalysts for Hydrazine‐Assisted Electrolytic Hydrogen Production

Electrocatalytic water splitting is one of the sustainable and promising strategies to generate hydrogen fuel but still remains a great challenge because of the sluggish anodic oxygen evolution reaction (OER). A very effective approach to dramatically decrease the input cell voltage of water electrolysis is to replace the anodic OER with hydrazine oxidation reaction (HzOR) due to its lower thermodynamic oxidation potential. Therefore, developing the low‐cost and efficient HzOR catalysts, coupled with the cathodic hydrogen evolution reaction (HER), is tremendously important for energy‐saving electrolytic hydrogen production. Herein, a new‐type of copper–nickel nitride (Cu₁Ni₂‐N) with rich Cu₄N/Ni₃N interface is rationally constructed on carbon fiber cloth. The 3D electrode exhibits extraordinary HER performance with an overpotential of 71.4 mV at 10 mA cm^?2 in 1.0 m KOH, simultaneously delivering an ultralow potential of 0.5 mV at 10 mA cm^?2 for HzOR in a 1.0 m KOH/0.5 m hydrazine electrolyte. Moreover, the electrolytic cell utilizing the synthesized Cu₁Ni₂‐N electrode as both the cathode and anode display a cell voltage of 0.24 V at 10 mA cm^?2 with an excellent stability over 75 h. The present work develops the promising copper–nickel‐based nitride as a bifunctional electrocatalyst through hydrazine‐assistance for energy‐saving electrolytic hydrogen production.     

Synergistically Tuning Water and Hydrogen Binding Abilities Over Co4N by Cr Doping for Exceptional Alkaline Hydrogen Evolution Electrocatalysis

Searching for highly efficient and cost‐effective electrocatalysts toward the hydrogen evolution reaction (HER) in alkaline electrolyte is highly desirable for the development of alkaline water splitting, but still remains a significant challenge. Herein, the rational design of Cr‐doped Co₄N nanorod arrays grown on carbon cloth (Cr–Co₄N/CC) that can efficiently catalyze the HER in alkaline media is reported. It displays outstanding performance, with the exceptionally small overpotential of 21 mV to obtain the current density of 10 mA cm^?2 and good stability in 1.0 m KOH, which is even better than the commercial Pt/C electrocatalyst, and much lower than most of the reported transition metal nitride‐based and other non‐noble metal‐based electrocatalysts toward the alkaline HER. Density functional theory (DFT) calculations and experimental results reveal that the Cr atoms not only act as oxophilic sites for boosting water adsorption and dissociation, but also modulate the electronic structure of Co₄N to endow optimized hydrogen binding abilities on Co atoms, thereby leading to accelerating both the alkaline Volmer and Heyrovsky reaction kinetics. In addition, this strategy can be extended to other metals (such as Mo, Mn, and Fe) doped Co₄N electrocatalysts, thus may open up a new avenue for the rational design of highly efficient transition metal nitride‐based HER catalysts and beyond.     

Unsaturated Sulfur Edge Engineering of Strongly Coupled MoS2 Nanosheet–Carbon Macroporous Hybrid Catalyst for Enhanced Hydrogen Generation

The low hydrogen adsorption free energy and strong acid/alkaline resistance of layered MoS₂ render it an excellent pH‐universal electrocatalyst for hydrogen evolution reaction (HER). However, the catalytic activity is dominantly suppressed by its limited active‐edge‐site density. Herein, a new strategy is reported for making a class of strongly coupled MoS₂ nanosheet–carbon macroporous hybrid catalysts with engineered unsaturated sulfur edges for boosting HER catalysis by controlling the precursor decomposition and subsequent sodiation/desodiation. Both surface chemical state analysis and first‐principles calculations verify that the resultant catalysts exhibit a desirable valence‐electron state with high exposure of unsaturated sulfur edges and an optimized hydrogen adsorption free energy, significantly improving the intrinsic HER catalytic activity. Such an electrocatalyst exhibits superior and stable catalytic activity toward HER with small overpotentials of 136 mV in 0.5 m H₂SO₄ and 155 mV in 1 m KOH at 10 mA cm^?2, which is the best report for MoS₂–C hybrid electrocatalysts to date. This work paves a new avenue to improve the intrinsic catalytic activity of 2D materials for hydrogen generation.     

Multifunctional Single‐Crystallized Carbonate Hydroxides as Highly Efficient Electrocatalyst for Full Water splitting

The controllable synthesis of single‐crystallized iron‐cobalt carbonate hydroxide nanosheets array on 3D conductive Ni foam (FCCH/NF) as a monolithic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) bifunctional electrocatalyst for full water splitting is described. The results demonstrate that the incorporation of Fe can effectively tune the morphology, composition, electronic structure, and electrochemical active surface area of the electrocatalysts, thus greatly enhancing the intrinsic electrocatalytic activity. The optimal electrocatalyst (F_0.25C₁CH/NF) can deliver 10 and 1000 mA cm^?2 at very small overpotentials of 77 and 256 mV for HER and 228 and 308 mV for OER in 1.0 m KOH without significant interference from gas evolution. The F_0.25C₁CH‐based two‐electrode alkaline water electrolyzer only requires cell voltages of 1.45 and 1.52 V to achieve current densities of 10 and 500 mA cm^?2. The results demonstrate that such fascinating electrocatalytic activity can be ascribed to the increase in the catalytic active surface area, facilitated electron and mass transport properties, and the synergistic interactions because of the incorporation of Fe.     

Dual‐Functional N Dopants in Edges and Basal Plane of MoS2 Nanosheets Toward Efficient and Durable Hydrogen Evolution

Herein, the authors explicitly reveal the dual‐functions of N dopants in molybdenum disulfide (MoS₂) catalyst through a combined experimental and first‐principles approach. The authors achieve an economical, ecofriendly, and most efficient MoS₂‐based hydrogen evolution reaction (HER) catalyst of N‐doped MoS₂ nanosheets, exhibiting an onset overpotential of 35 mV, an overpotential of 121 mV at 100 mA cm^?2 and a Tafel slope of 41 mV dec^?1. The dual‐functions of N dopants are (1) activating the HER catalytic activity of MoS₂ S‐edge and (2) enhancing the conductivity of MoS₂ basal plane to promote rapid charge transfer. Comprehensive electrochemical measurements prove that both the amount of active HER sites and the conductivity of N‐doped MoS₂ increase as a result of doping N. Systematic first‐principles calculations identify the active HER sites in N‐doped MoS₂ edges and also illustrate the conducting charges spreading over N‐doped basal plane induced by strong Mo 3d –S 2p –N 2p hybridizations at Fermi level. The experimental and theoretical research on the efficient HER catalysis of N‐doped MoS₂ nanosheets possesses great potential for future sustainable hydrogen production via water electrolysis and will stimulate further development on nonmetal‐doped MoS₂ systems to bring about novel high‐performance HER catalysts.     

Identifying Catalytic Active Sites of Trimolybdenum Phosphide (Mo3P) for Electrochemical Hydrogen Evolution

Solid‐state electrocatalysis plays a crucial role in the development of renewable energy to reshape current and future energy needs. However, finding an inexpensive and highly active catalyst to replace precious metals remains a big challenge for this technology. Here, tri‐molybdenum phosphide (Mo₃P) is found as a promising nonprecious metal and earth‐abundant candidate with outstanding catalytic properties that can be used for electrocatalytic processes. The catalytic performance of Mo₃P nanoparticles is tested in the hydrogen evolution reaction (HER). The results indicate an onset potential of as low as 21 mV, H₂ formation rate, and exchange current density of 214.7 µmol s^?1 g^?1_cat (at only 100 mV overpotential) and 279.07 µA cm^?2, respectively, which are among the closest values yet observed to platinum. Combined atomic‐scale characterizations and computational studies confirm that high density of molybdenum (Mo) active sites at the surface with superior intrinsic electronic properties are mainly responsible for the remarkable HER performance. The density functional theory calculation results also confirm that the exceptional performance of Mo₃P is due to neutral Gibbs free energy (ΔG_H*) of the hydrogen (H) adsorption at above 1/2 monolayer (ML) coverage of the (110) surface, exceeding the performance of existing non‐noble metal catalysts for HER.     

Engineered MoSe2‐Based Heterostructures for Efficient Electrochemical Hydrogen Evolution Reaction

2D transition metal‐dichalcogenides are emerging as efficient and cost‐effective electrocatalysts for the hydrogen evolution reaction (HER). However, only the edge sites of their trigonal prismatic phase show HER‐electrocatalytic properties, while the basal plane, which is absent of defective/unsaturated sites, is inactive. Herein, the authors tackle the key challenge of increasing the number of electrocatalytic sites by designing and engineering heterostructures composed of single‐/few‐layer MoSe₂ flakes and carbon nanomaterials (graphene or single‐wall carbon nanotubes) produced by solution processing. The electrochemical coupling between the materials that comprise the heterostructure effectively enhances the HER‐electrocatalytic activity of the native MoSe₂ flakes. The optimization of the mass loading of MoSe₂ flakes and their electrode assembly via monolithic heterostructure stacking provides a cathodic current density of 10 mA cm^?2 at overpotential of 100 mV, a Tafel slope of 63 mV dec^?1, and an exchange current density (j₀) of 0.203 µA cm^?2. In addition, thermal and chemical treatments are exploited to texturize the basal planes of the MoSe₂ flakes (through Se‐vacancies creation) and to achieve in situ semiconducting‐to‐metallic phase conversion, respectively, thus they activate new HER‐electrocatalytic sites. The as‐engineered electrodes show a 4.8‐fold enhancement of j₀ and a decrease in the Tafel slope to 54 mV dec^?1.     

Oriented Transformation of Co‐LDH into 2D/3D ZIF‐67 to Achieve Co–N–C Hybrids for Efficient Overall Water Splitting

Construction of well‐defined metal–organic framework precursor is vital to derive highly efficient transition metal–carbon‐based electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting. Herein, a novel strategy involving an in situ transformation of ultrathin cobalt layered double hydroxide into 2D cobalt zeolitic imidazolate framework (ZIF‐67) nanosheets grafted with 3D ZIF‐67 polyhedra supported on the surface of carbon cloth (2D/3D ZIF‐67@CC) precursor is proposed. After a low‐temperature pyrolysis, this precursor can be further converted into hybrid composites composed of ultrafine cobalt nanoparticles embedded within 2D N‐doped carbon nanosheets and 3D N‐doped hollow carbon polyhedra (Co@N‐CS/N‐HCP@CC). Experimental and density functional theory calculations results indicate that such composites have the advantages of a large number of accessible active sites, accelerated charge/mass transfer ability, the synergistic effect of components as well as an optimal water adsorption energy change. As a result, the obtained Co@N‐CS/N‐HCP@CC catalyst requires overpotentials of only 66 and 248 mV to reach a current density of 10 mA cm^?2 for HER and OER in 1.0 m KOH, respectively. Remarkably, it enables an alkali‐electrolyzer with a current density of 10 mA cm^?2 at a low cell voltage of 1.545 V, superior to that of the IrO₂@CC||Pt/C@CC couple (1.592 V).     

Nickel–Copper Alloy Encapsulated in Graphitic Carbon Shells as Electrocatalysts for Hydrogen Evolution Reaction

Searching for cost‐effective and high‐performance electrocatalysts for hydrogen production is of paramount importance. Herein, nickel‐copper (NiCu) alloy nanoparticles are encapsulated into graphitic shells via an ambient‐pressure chemical vapor deposition process. The resulting carbon‐encapsulated NiCu (denoted as NiCu@C) composite possesses a well‐defined core–shell structure with tunable thicknesses of the shells and is examined as electrocatalysts for the hydrogen evolution reaction (HER) in acidic, neutral, and alkaline solutions. Electrochemical measurements indicate that the activity of the NiCu@C highly depends on the thickness of the shell. Single‐layered graphene encapsulated NiCu nanoparticles show remarkable HER activity and durability. To obtain a current density of 10 mA cm^?2, overpotentials of 48, 164, and 74 mV are needed in electrolyte solutions with pH = 0, 7, and 14, respectively. Such low overpotentials render the composite as one of the most active nonprecious electrocatalysts. Accelerated durability tests demonstrate that the NiCu@C catalysts exhibit excellent stability. Density function theory calculations are conducted to investigate the electronic structures of the NiCu@C. It is found that the representative Ni₄₃Cu₁₂@C₂₄₀ model shows an ideal adsorption energy of hydrogen (?0.03 eV), manifesting its high HER activity.     

Corrosion and Alloy Engineering in Rational Design of High Current Density Electrodes for Efficient Water Splitting

Alongside rare‐earth metals, Ni, Fe, Co, Cu are some of the critical materials that will be in huge demand thanks to growth in clean‐energy sector. Herein scrap stainless steel wires (SSW) from worn‐out tires are employed as a support material for catalyst integration in the hydrogen evolution reaction (HER). In addition, SSW by corrosion engineering is exercised as an in situ formed freestanding robust electrode for the oxygen evolution reaction (OER). By superficial corrosion of SSW, inherent active species are unmasked in the form of Ni/FeOOH nanocrystallites displaying efficient water oxidation by reaching 500 mA cm^?2 at low overpotential (η₅₀₀) of 287 mV in 1 m KOH. Similarly, cathode scrap SSW with active (alloy) coatings of MoNi₄ catalyzes the HER at η_‐200 = 77 mV, with a low activation energy (E_a = 16.338 kJ mol^?1) and high durability of 150 h. Promisingly, when used in industrial conditions, 5 m KOH, 343 K, these electrodes demonstrate abnormal activity by yielding high anodic and cathodic current density of 1000 mA cm^?2 at η = 233 mV and η = 161 mV, respectively. This work may inspire researchers to explore and reutilize high‐demand metals from scrap for addressing critical material shortfalls in clean‐energy technologies.     

Self‐Assemble and In Situ Formation of Ni1−xFexPS3 Nanomosaic‐Decorated MXene Hybrids for Overall Water Splitting

Herein, the authors present the development of novel 0D–2D nanohybrids consisting of a nickel‐based bimetal phosphorus trisulfide (Ni_1?xFe_xPS₃) nanomosaic that decorates on the surface of MXene nanosheets (denoted as NFPS@MXene). The nanohybrids are obtained through a facile self‐assemble process of transition metal layered double hydroxide (TMLDH) on MXene surface; followed by a low temperature in situ solid‐state reaction step. By tuning the Ni:Fe ratio, the as‐synthesized NFPS@MXene nanohybrids exhibit excellent activities when tested as electrocatalysts for overall water splitting. Particularly, with the initial Ni:Fe ratio of 7:3, the obtained Ni_0.7Fe_0.3PS₃@MXene nanohybrid reveals low overpotential (282 mV) and Tafel slope (36.5 mV dec^?1) for oxygen evolution reaction (OER) in 1 m KOH solution. Meanwhile, the Ni_0.9Fe_0.1PS₃@MXene shows low overpotential (196 mV) for the hydrogen evolution reaction (HER) in 1 m KOH solution. When integrated for overall water splitting, the Ni_0.7Fe_0.3PS₃@MXene || Ni_0.9Fe_0.1PS₃@MXene couple shows a low onset potential of 1.42 V and needs only 1.65 V to reach a current density of 10 mA cm^?2, which is better than the all noble metal IrO₂ || Pt/C electrocatalyst (1.71 mV@10 mA cm^?2). Given the chemical versatility of Ni_1?xFe_xPS₃ and the convenient self‐assemble process, the nanohybrids demonstrated in this work are promising for energy conversion applications.     

Surface Engineering of 3D Gas Diffusion Electrodes for High‐Performance H2 Production with Nonprecious Metal Catalysts

In this work, a methodology is demonstrated to engineer gas diffusion electrodes for nonprecious metal catalysts. Highly active transition metal phosphides are prepared on carbon‐based gas diffusion electrodes with low catalyst loadings by modifying the O/C ratio at the surface of the electrode. These nonprecious metal catalysts yield extraordinary performance as measured by low overpotentials (51 mV at ?10 mA cm^?2), unprecedented mass activities (>800 A g^?1 at 100 mV overpotential), high turnover frequencies (6.96 H₂ s^?1 at 100 mV overpotential), and high durability for a precious metal‐free catalyst in acidic media. It is found that a high O/C ratio induces a more hydrophilic surface directly impacting the morphology of the CoP catalyst. The improved hydrophilicity, stemming from introduced oxyl groups on the carbon electrode, creates an electrode surface that yields a well‐distributed growth of cobalt electrodeposits and thus a well‐dispersed catalyst layer with high surface area upon phosphidation. This report demonstrates the high‐performance achievable by CoP at low loadings which facilitates further cost reduction, an important part of enabling the large‐scale commercialization of non‐platinum group metal catalysts. The fabrication strategies described herein offer a pathway to lower catalyst loading while achieving high efficiency and promising stability on a 3D electrode.     

Self‐Limited on‐Site Conversion of MoO3 Nanodots into Vertically Aligned Ultrasmall Monolayer MoS2 for Efficient Hydrogen Evolution

MoS₂ has emerged as a promising alternative electrocatalyst for the hydrogen evolution reaction (HER) due to high intrinsic per‐site activity on its edge sites and S‐vacancies. However, a significant challenge is the limited density of such sites. Reducing the size and layer number of MoS₂ and vertically aligning them would be an effective way to enrich and expose such sites for HER. Herein, a facile self‐limited on‐site conversion strategy for synthesizing monolayer MoS₂ in a couple of nanometers which are highly dispersed and vertically aligned on 3D porous carbon sheets is reported. It is discovered that the preformation of well‐dispersed MoO₃ nanodots in 1–2 nm as limited source is the key for the fabrication of such an ultrasmall MoS₂ monolayer. As indicated by X‐ray photoelectron spectroscopy and electron spin resonance data, these ultrasmall MoS₂ monolayers are rich in accessible S‐edge sites and vacancies and the smaller MoS₂ monolayers the more such sites they have, leading to enhanced electrocatalytic activity with a low overpotential of 126 mV at 10 mA cm^?2 and 140 mV at 100 mA mg^?1 for HER. This state‐of‐the‐art performance for MoS₂ electrocatalysts enables the present strategy as a new avenue for exploring well‐dispersed ultrasmall nanomaterials as efficient catalysts.     

Ni3+‐Induced Formation of Active NiOOH on the Spinel Ni–Co Oxide Surface for Efficient Oxygen Evolution Reaction

Efficient and earth abundant electrocatalysts for high‐performance oxygen evolution reaction (OER) are essential for the development of sustainable energy conversion technologies. Here, a new hierarchical Ni–Co oxide nanostructure, composed of small secondary nanosheets grown on primary nanosheet arrays, is synthesized via a topotactic transformation of Ni–Co layered double hydroxide. The Ni³⁺‐rich surface benefits the formation of NiOOH, which is the main redox site as revealed via in situ X‐ray absorption near edge structure and extended X‐ray absorption fine structure spectroscopy. The Ni–Co oxide hierarchical nanosheets (NCO–HNSs) deliver a stable current density of 10 mA cm^?2 at an overpotential of ≈0.34 V for OER with a Tafel slope of as low as 51 mV dec^?1 in alkaline media. The improvement in the OER activity can be ascribed to the synergy of large surface area offered by the 3D hierarchical nanostructure and the facile formation of NiOOH as the main active sites on the surface of NCO–HNSs to decrease the overpotential and facilitate the catalytic reaction.