Polyaniline Derived N‐Doped Carbon‐Coated Cobalt Phosphide Nanoparticles Deposited on N‐Doped Graphene as an Efficient Electrocatalyst for Hydrogen Evolution Reaction

The development of highly efficient and durable non‐noble metal electrocatalysts for the hydrogen evolution reaction (HER) is significant for clean and renewable energy research. This work reports the synthesis of N‐doped graphene nanosheets supported N‐doped carbon coated cobalt phosphide (CoP) nanoparticles via a pyrolysis and a subsequent phosphating process by using polyaniline. The obtained electrocatalyst exhibits excellent electrochemical activity for HER with a small overpotential of ?135 mV at 10 mA cm^?2 and a low Tafel slope of 59.3 mV dec^?1 in 0.5 m H₂SO₄. Additionally, the encapsulation of N‐doped carbon shell prevents CoP nanoparticles from corrosion, exhibiting good stability after 14 h operation. Moreover, the as‐prepared electrocatalyst also shows outstanding activity and stability in basic and neutral electrolytes.     

Cobalt Phosphide Composite Encapsulated within N,P‐Doped Carbon Nanotubes for Synergistic Oxygen Evolution

Exploring highly efficient and stable oxygen evolution reaction (OER) electrocatalysts such as transition‐metal phosphides (TMPs) is critical to advancing renewable hydrogen fuel. TMP nanostructures typically involving binary or ternary TMPs tuned by cation or anion doping are suggested to be promising low‐cost and durable OER catalysts. Herein, the preparation of CoP/CoP₂ composite nanoparticles encapsulated within N,P‐doped carbon nanotubes (CoP/CoP₂@NPCNTs) is demonstrated as a synergistic electrocatalyst for OER via the calcination of a CoAl‐layered double hydroxide/melamine mixture and subsequent phosphorization. Facile visualization by scanning electron microscopy in conjunction with electron backscatter diffraction demonstrates the encapsulation of the CoP/CoP₂ nanoparticles within the N,P‐codoped CNTs. Electrocatalytic evaluation shows that the composite electrode requires a low overpotential of 300 mV for the OER at 10 mA cm^?2 in a 1.0 m KOH solution and, in particular, exhibits an excellent long‐term durability of ≈100 h, which is superior to that of the state‐of‐the‐art RuO₂ electrocatalyst. Density functional theory calculations reveal that the synergistic effect of CoP and CoP₂ can enhance the electrocatalytic performance. In addition, molecular dynamics simulations demonstrate that the generated O₂ molecules can readily diffuse out of the CNTs. Both the effects give rise to the observed OER enhancement.     

Graphene Decorated with Uniform Ultrathin (CoP)x–(FeP)1–x Nanorods: A Robust Non‐Noble‐Metal Catalyst for Hydrogen Evolution

Developing high‐performance but low‐cost hydrogen evolution reaction (HER) electrocatalysts with superior activity and stability for future sustainable energy conversion technologies is highly desired. Tuning of microstructure, configuration, and chemical composition are paramount to developing effective non‐noble electrocatalysts for HER. Herein, a universal “nanocasting” method is reported to construct graphene decorated with uniform ternary (CoP)_x –(FeP)_1?x (0 ≤ x ≤ 1) nanorods hybrids with different chemical compositions [(CoP)_x –(FeP)_1?x –NRs/G] as a highly active and durable nonprecious‐metal electrocatalyst for the HER. The optimized (CoP)_0.54–(FeP)_0.46–NRs/G electrocatalyst exhibits overpotentials of as low as 57 and 97 mV at 10 mA cm^?2, Tafel slopes of 52 and 62 mV dec^?1, exchange current densities of 0.489 and 0.454 mA cm^?2, and Faradaic efficiency of nearly 100% in acidic and alkaline media, respectively. More importantly, this electrocatalyst also exhibits high tolerance and durability in a wide pH range and keeps catalytic activity for at least 3000 cycles and 24 h of sustained hydrogen production. The excellent catalytic performance of the (CoP)_x –(FeP)_1?x –NRs/G electrocatalyst may be ascribed to its unique mesoporous structure and strong synergistic effect between CoP and FeP. Thus, the work provides a feasible way to fabricate cheap and highly efficient electrocatalyst as alternatives for Pt‐based electrocatalysts for HER in electrochemical water splitting.     

Oxygen Vacancy–Rich In‐Doped CoO/CoP Heterostructure as an Effective Air Cathode for Rechargeable Zn–Air Batteries

An efficient and low‐cost electrocatalyst for reversible oxygen electrocatalysis is crucial for improving the performance of rechargeable metal?air batteries. Herein, a novel oxygen vacancy–rich 2D porous In‐doped CoO/CoP heterostructure (In‐CoO/CoP FNS) is designed and developed by a facile free radicals–induced strategy as an effective bifunctional electrocatalyst for rechargeable Zn–air batteries. The electron spin resonance and X‐ray absorption near edge spectroscopy provide clear evidence that abundant oxygen vacancies are formed in the interface of In‐CoO/CoP FNS. Owing to abundant oxygen vacancies, porous heterostructure, and multiple components, In‐CoO/CoP FNS exhibits excellent oxygen reduction reaction activity with a positive half‐wave potential of 0.81 V and superior oxygen evolution reaction activity with a low overpotential of 365 mV at 10 mA cm^?2. Moreover, a home‐made Zn–air battery with In‐CoO/CoP FNS as an air cathode delivers a large power density of 139.4 mW cm^?2, a high energy density of 938 Wh kg_Zn^?1, and can be steadily cycled over 130 h at 10 mA cm^?2, demonstrating great application potential in rechargeable metal–air batteries.     

Exceptional Performance of Hierarchical Ni–Fe (hydr)oxide@NiCu Electrocatalysts for Water Splitting

Developing low‐cost bifunctional electrocatalysts with superior activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of great importance for the widespread application of the water splitting technique. In this work, using earth‐abundant transition metals (i.e., nickel, iron, and copper), 3D hierarchical nanoarchitectures, consisting of ultrathin Ni–Fe layered‐double‐hydroxide (Ni–Fe LDH) nanosheets or porous Ni–Fe oxides (NiFeO_x) assembled to a metallic NiCu alloy, are delicately constructed. In alkaline solution, the as‐prepared Ni–Fe LDH@NiCu possesses outstanding OER activity, achieving a current density of 10 mA cm^?2 at an overpotential of 218 mV, which is smaller than that of RuO₂ catalyst (249 mV). In contrast, the resulting NiFeO_x@NiCu exhibits better HER activity, yielding a current density of 10 mA cm^?2 at an overpotential of 66 mV, which is slightly higher than that of Pt catalyst (53 mV) but superior to all other transition metal (hydr)oxide‐based electrocatalysts. The remarkable activity of the Ni–Fe LDH@NiCu and NiFeO_x@NiCu is further demonstrated by a 1.5 V solar‐panel‐powered electrolyzer, resulting in current densities of 10 and 50 mA cm^?2 at overpotentials of 293 and 506 mV, respectively. Such performance renders the as‐prepared materials as the best bifunctional electrocatalysts so far.     

A Heterostructure Coupling of Exfoliated Ni–Fe Hydroxide Nanosheet and Defective Graphene as a Bifunctional Electrocatalyst for Overall Water Splitting

Herein, the authors demonstrate a heterostructured NiFe LDH‐NS@DG10 hybrid catalyst by coupling of exfoliated Ni–Fe layered double hydroxide (LDH) nanosheet (NS) and defective graphene (DG). The catalyst has exhibited extremely high electrocatalytic activity for oxygen evolution reaction (OER) in an alkaline solution with an overpotential of 0.21 V at a current density of 10 mA cm^?2, which is comparable to the current record (≈0.20 V in Fe–Co–Ni metal‐oxide‐film system) and superior to all other non‐noble metal catalysts. Also, it possesses outstanding kinetics (Tafel slope of 52 mV dec^?1) for the reaction. Interestingly, the NiFe LDH‐NS@DG10 hybrid has also exhibited the high hydrogen evolution reaction (HER) performance in an alkaline solution (with an overpotential of 115 mV by 2 mg cm^?2 loading at a current density of 20 mA cm^?2) in contrast to barely HER activity for NiFe LDH‐NS itself. As a result, the bifunctional catalyst the authors developed can achieve a current density of 20 mA cm^?2 by a voltage of only 1.5 V, which is also a record for the overall water splitting. Density functional theory calculation reveals that the synergetic effects of highly exposed 3d transition metal atoms and carbon defects are essential for the bifunctional activity for OER and HER.     

Rational Design and Synthesis of Extremely Efficient Macroporous CoSe2–CNT Composite Microspheres for Hydrogen Evolution Reaction

Uniquely structured CoSe₂–carbon nanotube (CNT) composite microspheres with optimized morphology for the hydrogen‐evolution reaction (HER) are prepared by spray pyrolysis and subsequent selenization. The ultrafine CoSe₂ nanocrystals uniformly decorate the entire macroporous CNT backbone in CoSe₂–CNT composite microspheres. The macroporous CNT backbone strongly improves the electrocatalytic activity of CoSe₂ by improving the electrical conductivity and minimizing the growth of CoSe₂ nanocrystals during the synthesis process. In addition, the macroporous structure resulting from the CNT backbone improves the electrocatalytic activity of the CoSe₂–CNT microspheres by increasing the removal rate of generated H₂ and minimizing the polarization of the electrode during HER. The CoSe₂–CNT composite microspheres demonstrate excellent catalytic activity for HER in an acidic medium (10 mA cm^?2 at an overpotential of ≈174 mV). The bare CoSe₂ powders exhibit moderate HER activity, with an overpotential of 226 mV at 10 mA cm^?2. The Tafel slopes for the CoSe₂–CNT composite and bare CoSe₂ powders are 37.8 and 58.9 mV dec^?1, respectively. The CoSe₂–CNT composite microspheres have a slightly larger Tafel slope than that of commercial carbon‐supported platinum nanoparticles, which is 30.2 mV dec^–1.     

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.     

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.     

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.     

Single Ni Atoms and Clusters Embedded in N‐Doped Carbon “Tubes on Fibers” Matrix with Bifunctional Activity for Water Splitting at High Current Densities

Among the bifunctional catalysts for water splitting, recently emerged transition‐metal single‐atom catalysts are theoretically considered to possess high potential, while the experimental activity is not satisfactory yet. Herein, an exceptionally efficient trifunctional metal–nitrogen–carbon (M–N–C) catalyst electrode, composed of a hierarchical carbon matrix embedding isolated nickel atoms with nickel–iron (NiFe) clusters, is presented. 1D microfibers and nanotubes grow sequentially from 2D nanosheets as sacrificial templates via two stages of solution‐ and solid‐phase reactions to form a 1D hierarchy. Exceptionally efficient bifunctional activity with an overpotential of only 13 mV at 10 mA cm^?2 toward hydrogen evolution reaction (HER) and an overpotential of 210 mV at 30 mA cm^?2 toward oxygen evolution reaction (OER) is obtained, surpassing each monofunctional activity ever reported. More importantly, an overpotential of only 126 and 326 mV is required to drive 500 mA cm^?2 toward the HER and OER, respectively. For the first time, industrial‐scale water splitting with two bifunctional catalyst electrodes with a current density of 500 mA cm^?2 at a potential of 1.71 V is demonstrated. Lastly, trifunctional catalytic activity including oxygen reduction reaction is also proven with a half‐wave potential at 0.848 V.     

Active Sites Intercalated Ultrathin Carbon Sheath on Nanowire Arrays as Integrated Core–Shell Architecture: Highly Efficient and Durable Electrocatalysts for Overall Water Splitting

The development of active bifunctional electrocatalysts with low cost and earth‐abundance toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains a great challenge for overall water splitting. Herein, metallic Ni₄Mo nanoalloys are firstly implanted on the surface of NiMoO_x nanowires array (NiMo/NiMoO_x ) as metal/metal oxides hybrid. Inspired by the superiority of carbon conductivity, an ultrathin nitrogen‐doped carbon sheath intercalated NiMo/NiMoO_x (NC/NiMo/NiMoO_x ) nanowires as integrated core–shell architecture are constructed. The integrated NC/NiMo/NiMoO_x array exhibits an overpotential of 29 mV at 10 mA cm^?2 and a low Tafel slope of 46 mV dec^?1 for HER due to the abundant active sites, fast electron transport, low charge‐transfer resistance, unique architectural structure and synergistic effect of carbon sheath, nanoalloys, and oxides. Moreover, as OER catalysts, the NC/NiMo/NiMoO_x hybrids require an overpotential of 284 mV at 10 mA cm^?2. More importantly, the NC/NiMo/NiMoO_x array as a highly active and stable electrocatalyst approaches ≈10 mA cm^?2 at a voltage of 1.57 V, opening an avenue to the rational design and fabrication of the promising electrode materials with architecture structures toward the electrochemical energy storage and conversion.     

Ferrocene‐Incorporated Cobalt Sulfide Nanoarchitecture for Superior Oxygen Evolution Reaction

Here, ferrocene(Fc)‐incorporated cobalt sulfide (Co_xS_y) nanostructures directly grown on carbon nanotube (CNT) or carbon fiber (CF) networks for electrochemical oxygen evolution reaction (OER) using a facile one‐step solvothermal method are reported. The strong synergistic interaction between Fc‐Co_xS_y nanostructures and electrically conductive CNTs results in the superior electrocatalytic activity with a very small overpotential of ≈304 mV at 10 mA cm^?2 and a low Tafel slope of 54.2 mV dec^?1 in 1 m KOH electrolyte. Furthermore, the Fc‐incorporated Co_xS_y (FCoS) nanostructures are directly grown on the acid pretreated carbon fiber (ACF), and the resulting fabricated electrode delivers excellent OER performance with a low overpotential of ≈315 mV at 10 mA cm^?2. Such superior OER catalytic activity can be attributed to 3D Fc‐Co_xS_y nanoarchitectures that consist of a high concentration of vertical nanosheets with uniform distribution of nanoparticles that afford a large number of active surface areas and edge sites. Besides, the tight contact interface between ACF substrate and Fc‐Co_xS_y nanostructures could effectively facilitate the electron transfer rate in the OER. This study provides valuable insights for the rational design of energy storage and conversion materials by the incorporation of other transition metal into metal sulfide/oxide nanostructures utilizing metallocene.     

Co9S8 Nanoparticles‐Embedded N/S‐Codoped Carbon Nanofibers Derived from Metal–Organic Framework‐Wrapped CdS Nanowires for Efficient Oxygen Evolution Reaction

Metal–organic frameworks (MOFs) with tunable compositions and morphologies are recognized as efficient self‐sacrificial templates to achieve function‐oriented nanostructured materials. Moreover, it is urgently needed to develop highly efficient noble metal‐free oxygen evolution reaction (OER) electrocatalysts to accelerate the development of overall water splitting green energy conversion systems. Herein, a facile and cost‐efficient strategy to synthesize Co₉S₈ nanoparticles‐embedded N/S‐codoped carbon nanofibers (Co₉S₈/NSCNFs) as highly active OER catalyst is developed. The hybrid precursor of core–shell ZIF‐wrapped CdS nanowires is first prepared and then leads to the formation of uniformly dispersed Co₉S₈/N, S‐codoped carbon nanocomposites through a one‐step calcination reaction. The optimal Co₉S₈/NSCNFs‐850 is demonstrated to possess excellent electrocatalytic performance for OER in 1.0 m KOH solution, affording a low overpotential of 302 mV to reach the current density of 10 mA cm^?2, a small Tafel slope of 54 mV dec^?1, and superior long‐term stability for 1000 cyclic voltammetry cycles. The favorable results raise a concept of exploring more MOF‐based nanohybrids as precursors to induce the synthesis of novel porous nanomaterials as non‐noble‐metal electrocatalysts for sustainable energy conversion.     

Ambient Fast Synthesis and Active Sites Deciphering of Hierarchical Foam‐Like Trimetal–Organic Framework Nanostructures as a Platform for Highly Efficient Oxygen Evolution Electrocatalysis

Metal–organic frameworks (MOFs) have attracted tremendous interest due to their promising applications including electrocatalysis originating from their unique structural features. However, it remains a challenge to directly use MOFs for oxygen electrocatalysis because it is quite difficult to manipulate their dimension, composition, and morphology of the MOFs with abundant active sites. Here, a facile ambient temperature synthesis of unique NiCoFe‐based trimetallic MOF nanostructures with foam‐like architecture is reported, which exhibit extraordinary oxygen evolution reaction (OER) activity as directly used catalyst in alkaline condition. Specifically, the (Ni₂Co₁)_0.925Fe_0.075‐MOF‐NF delivers a minimum overpotential of 257 mV to reach the current density of 10 mA cm^?2 with a small Tafel slope of 41.3 mV dec^?1 and exhibits high durability after long‐term testing. More importantly, the deciphering of the possible origination of the high activity is performed through the characterization of the intermediates during the OER process, where the electrochemically transformed metal hydroxides and oxyhydroxides are confirmed as the active species.     

Amorphous Molybdenum Sulfide/Carbon Nanotubes Hybrid Nanospheres Prepared by Ultrasonic Spray Pyrolysis for Electrocatalytic Hydrogen Evolution

Developing cost‐effective electrocatalysts with high activity and stability for hydrogen evolution reaction (HER) plays an important role in modern hydrogen economy. Amorphous molybdenum sulfide (MoS_x ) has recently emerged as one of the most promising alternatives to Pt‐based catalysts in HER, especially in acidic electrolytes. Here this study reports a simple ultrasonic spray pyrolysis method to synthesize hybrid HER catalysts composed of MoS_x firmly attached on entangled carbon nanotube nanospheres (MoS_x /CNTs). This synthetic process is fast, continuous, highly durable, and amenable to high‐volume production with high yields and exceptional quality. The MoS_x /CNTs hybrid catalyst prepared at 300 °C exhibits a low overpotential of 168 mV at the current density of 10 mA cm^?2 with a small Tafel slope of 36 mV dec^?1. Electrochemical measurements and X‐ray photoelectron spectroscopy analyses reveal that the CNT network not only promotes the charge transfer in corresponding HER process but also enhances the stability of the active sites in MoS_x . This work demonstrates that ultrasonic spray pyrolysis is a reliable and versatile approach for synthesizing amorphous MoS_x‐based HER catalysts.     

Single Tungsten Atoms Supported on MOF‐Derived N‐Doped Carbon for Robust Electrochemical Hydrogen Evolution

Tungsten‐based catalysts are promising candidates to generate hydrogen effectively. In this work, a single‐W‐atom catalyst supported on metal–organic framework (MOF)‐derived N‐doped carbon (W‐SAC) for efficient electrochemical hydrogen evolution reaction (HER), with high activity and excellent stability is reported. High‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and X‐ray absorption fine structure (XAFS) spectroscopy analysis indicate the atomic dispersion of the W species, and reveal that the W₁N₁C₃ moiety may be the favored local structure for the W species. The W‐SAC exhibits a low overpotential of 85 mV at a current density of 10 mA cm^?2 and a small Tafel slope of 53 mV dec^?1, in 0.1 m KOH solution. The HER activity of the W‐SAC is almost equal to that of commercial Pt/C. Density functional theory (DFT) calculation suggests that the unique structure of the W₁N₁C₃ moiety plays an important role in enhancing the HER performance. This work gives new insights into the investigation of efficient and practical W‐based HER catalysts.     

Cactus‐Like Hollow Cu2‐xS@Ru Nanoplates as Excellent and Robust Electrocatalysts for the Alkaline Hydrogen Evolution Reaction

The development of Pt‐free electrocatalysts for the hydrogen evolution reaction (HER) recently is a focus of great interest. While several strategies are developed to control the structural properties of non‐Pt catalysts and boost their electrocatalytic activities for the HER, the generation of highly reactive defects or interfaces by combining a metal with other metals, or with metal oxides/sulfides, can lead to notably enhanced catalytic performance. Herein, the preparation of cactus‐like hollow Cu_2‐x S@Ru nanoplates (NPs) that contain metal/metal sulfide heterojunctions and show excellent catalytic activity and durability for the HER in alkaline media is reported. The initial formation of Ru islands on presynthesized Cu_1.94S NPs, via cation exchange between three Cu⁺ ions and one Ru³⁺, induces the growth of the Ru phase, which is concomitant with the dissolution of the Cu_1.94S nanotemplate, culminating in the formation of a hollow nanostructure with numerous thin Ru pillars. Hollow Cu_2‐x S@Ru NPs exhibit a small overpotential of 82 mV at a current density of ?10 mA cm^?2 and a low Tafel slope of 48 mV dec^?1 under alkaline conditions; this catalyst is among state‐of‐the‐art HER electrocatalysts in alkaline media. The excellent performance of hollow Cu_2‐x S@Ru NPs originates from the facile dissociation of water in the Volmer step.     

Strongly Coupled Nickel–Cobalt Nitrides/Carbon Hybrid Nanocages with Pt‐Like Activity for Hydrogen Evolution Catalysis

Designing non‐precious‐metal catalysts with comparable mass activity to state‐of‐the‐art noble‐metal catalysts for the hydrogen evolution reaction (HER) in alkaline solution still remains a significant challenge. Herein a new strongly coupled nickel–cobalt nitrides/carbon complex nanocage (NiCoNzocage) is rationally designed via chemical etching of ZIF‐67 nanocubes with Ni(NO₃)₂ under sonication at room temperature, following nitridation. The as‐prepared strongly coupled NiCoN/C nanocages exhibit a mass activity of 0.204 mA µg^?1 at an overpotential of 200 mV for the HER in alkaline solution, which is comparable to that of commercial Pt/C (0.451 mA µg^?1). The strongly coupled NiCoN/C nanocages also possess superior stability for the HER with negligible current loss under the overpotentials of 200 mV for 10 h. Density functional theory (DFT) calculations reveal that the excellent HER performance under alkaline condition arises from the robust Co²⁺→Co⁰ transformation achieved by strong (Ni, Co)? N‐bonding‐induced efficient d‐p‐d coupled electron transfer, which is a key for optimal initial water adsorption and splitting. The high degree of amorphization urges the C‐sites to be an electron‐pushing bath to promote the inter‐layer/sites electron‐transfer with loss of the orbital‐selection‐forbidden‐rule, which uniformly boosts the surface catalytic activities up to a high level independent of the individual surface active sites.     

Self‐Supportive Mesoporous Ni/Co/Fe Phosphosulfide Nanorods Derived from Novel Hydrothermal Electrodeposition as a Highly Efficient Electrocatalyst for Overall Water Splitting

Low cost and highly efficient bifuctional catalysts for overall water electrolysis have drawn considerable interests over the past several decades. Here, rationally synthesized mesoporous nanorods of nickel–cobalt–iron–sulfur–phosphorus composites are tightly self‐supported on Ni foam as a high‐performance, low cost, and stable bifunctional electrocatalyst for water electrolysis. The targeted designing and rational fabrication give rise to the nanorod‐like morphology with large surface area and excellent conductivity. The NiCoFe‐PS nanorod/NF can reach 10 mA cm^?2 at a small overpotential of 195 mV with a Tafel slope of 40.3 mV dec^?1 for the oxygen evolution reaction and 97.8 mV with 51.8 mV dec^?1 for the hydrogen evolution reaction. Thus, this bifunctional catalyst shows low potentials of 1.52 and 1.76 V at 10 and 50 mA cm^?2 toward overall water splitting with excellent stability for over 200 h, which are superior to most non‐noble metal‐based bifunctional electrocatalysts recently. This work provides a new strategy to fabricate multiple metal‐P/S composites with the mesoporous nanorod‐like structure as bifunctional catalysts for overall water splitting.