Carbon Nanotubes Decorated with CoP Nanocrystals: A Highly Active Non‐Noble‐Metal Nanohybrid Electrocatalyst for Hydrogen Evolution

The development of effective and inexpensive hydrogen evolution reaction (HER) electrocatalysts for future renewable energy systems is highly desired. The strongly acidic conditions in proton exchange membranes create a need for acid‐stable HER catalysts. A nanohybrid that consists of carbon nanotubes decorated with CoP nanocrystals (CoP/CNT) was prepared by the low‐temperature phosphidation of a Co₃O₄/CNT precursor. As a novel non‐noble‐metal HER catalyst operating in acidic electrolytes, the nanohybrid exhibits an onset overpotential of as low as 40 mV, a Tafel slope of 54 mV dec^?1, an exchange current density of 0.13 mA cm^?2, and a Faradaic efficiency of nearly 100 %. This catalyst maintains its catalytic activity for at least 18 hours and only requires overpotentials of 70 and 122 mV to attain current densities of 2 and 10 mA cm^?2, respectively.     

Graphitic Carbon Nitride Nanoribbons: Graphene‐Assisted Formation and Synergic Function for Highly Efficient Hydrogen Evolution

The development of new promising metal‐free catalysts is of great significance for the electrocatalytic hydrogen evolution reaction (HER). Herein, a rationally assembled three‐dimensional (3D) architecture of 1D graphitic carbon nitride (g‐C₃N₄) nanoribbons with 2D graphene sheets has been developed by a one‐step hydrothermal method. Because of the multipathway of charge and mass transport, the hierarchically structured g‐C₃N₄ nanoribbon–graphene hybrids lead to a high electrocatalytic ability for HER with a Tafel slope of 54 mV decade^?1, a low onset overpotential of 80 mV and overpotential of 207 mV to approach a current of 10 mA cm^?2, superior to those non‐metal materials and well‐developed metallic catalysts reported previously. This work presents a great advance for designing and developing highly efficient metal‐free catalyst for hydrogen evolution.     

Ultrafine Molybdenum Carbide Nanoparticles Composited with Carbon as a Highly Active Hydrogen‐Evolution Electrocatalyst

The replacement of platinum with non‐precious‐metal electrocatalysts with high efficiency and superior stability for the hydrogen‐evolution reaction (HER) remains a great challenge. Herein, we report the one‐step synthesis of uniform, ultrafine molybdenum carbide (Mo₂C) nanoparticles (NPs) within a carbon matrix from inexpensive starting materials (dicyanamide and ammonium molybdate). The optimized catalyst consisting of Mo₂C NPs with sizes lower than 3 nm encapsulated by ultrathin graphene shells (ca. 1–3 layers) showed superior HER activity in acidic media, with a very low onset potential of ?6 mV, a small Tafel slope of 41 mV dec^?1, and a large exchange current density of 0.179 mA cm^?2, as well as good stability during operation for 12 h. These excellent properties are similar to those of state‐of‐the‐art 20 % Pt/C and make the catalyst one of the most active acid‐stable electrocatalysts ever reported for HER.     

Nanoporous Graphene with Single‐Atom Nickel Dopants: An Efficient and Stable Catalyst for Electrochemical Hydrogen Production

Single‐atom nickel dopants anchored to three‐dimensional nanoporous graphene can be used as catalysts of the hydrogen evolution reaction (HER) in acidic solutions. In contrast to conventional nickel‐based catalysts and graphene, this material shows superior HER catalysis with a low overpotential of approximately 50 mV and a Tafel slope of 45 mV dec^?1 in 0.5 M H₂SO₄ solution, together with excellent cycling stability. Experimental and theoretical investigations suggest that the unusual catalytic performance of this catalyst is due to sp–d orbital charge transfer between the Ni dopants and the surrounding carbon atoms. The resultant local structure with empty C–Ni hybrid orbitals is catalytically active and electrochemically stable.     

Phosphorus‐Modified Tungsten Nitride/Reduced Graphene Oxide as a High‐Performance,Non‐Noble‐Metal Electrocatalyst for the Hydrogen Evolution Reaction

Phosphorus‐modified tungsten nitride/reduced graphene oxide (P‐WN/rGO) is designed as a high‐efficient, low‐cost electrocatalyst for the hydrogen evolution reaction (HER). WN (ca. 3 nm in size) on rGO is first synthesized by using the H₃[PO₄(W₃O₉)₄] cluster as a W source. Followed by phosphorization, the particle size increase slightly to about 4 nm with a P content of 2.52 at %. The interaction of P with rGO and WN results in an obvious increase of work function, being close to Pt metal. The P‐WN/rGO exhibits low onset overpotential of 46 mV, Tafel slope of 54 mV dec^?1, and a large exchange current density of 0.35 mA cm^?2 in acid media. It requires overpotential of only 85 mV at current density of 10 mA cm^?2, while remaining good stability in accelerated durability testing. This work shows that the modification with a second anion is powerful way to design new catalysts for HER.     

Heterostructured Inter‐Doped Ruthenium–Cobalt Oxide Hollow Nanosheet Arrays for Highly Efficient Overall Water Splitting

The development of transition‐metal‐oxides (TMOs)‐based bifunctional catalysts toward efficient overall water splitting through delicate control of composition and structure is a challenging task. Herein, the rational design and controllable fabrication of unique heterostructured inter‐doped ruthenium–cobalt oxide [(Ru–Co)O_x] hollow nanosheet arrays on carbon cloth is reported. Benefiting from the desirable compositional and structural advantages of more exposed active sites, optimized electronic structure, and interfacial synergy effect, the (Ru–Co)O_x nanoarrays exhibited outstanding performance as a bifunctional catalyst. Particularly, the catalyst showed a remarkable hydrogen evolution reaction (HER) activity with an overpotential of 44.1 mV at 10 mA cm^?2 and a small Tafel slope of 23.5 mV dec^?1, as well as an excellent oxygen evolution reaction (OER) activity with an overpotential of 171.2 mV at 10 mA cm^?2. As a result, a very low cell voltage of 1.488 V was needed at 10 mA cm^?2 for alkaline overall water splitting.     

Porous Molybdenum‐Based Hybrid Catalysts for Highly Efficient Hydrogen Evolution

We have synthesized a porous Mo‐based composite obtained from a polyoxometalate‐based metal–organic framework and graphene oxide (POMOFs/GO) using a simple one‐pot method. The MoO₂@PC‐RGO hybrid material derived from the POMOFs/GO composite is prepared at a relatively low carbonization temperature, which presents a superior activity for the hydrogen‐evolution reaction (HER) in acidic media owing to the synergistic effects among highly dispersive MoO₂ particles, phosphorus‐doped porous carbon, and RGO substrates. MoO₂@PC‐RGO exhibits a very positive onset potential close to that of 20 % Pt/C, low Tafel slope of 41 mV dec^?1, high exchange current density of 4.8×10^?4 A cm^?2, and remarkable long‐term cycle stability. It is one of the best high‐performance catalysts among the reported nonprecious metal catalysts for HER to date.     

Dual Graphitic‐N Doping in a Six‐Membered C‐Ring of Graphene‐Analogous Particles Enables an Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Graphene‐based materials still exhibit poor electrocatalytic activities for the hydrogen evolution reaction (HER) although they are considered to be the most promising electrocatalysts. We fabricated a graphene‐analogous material displaying exceptional activity towards the HER under acidic conditions with an overpotential (57 mV at 10 mA cm^?2) and Tafel slope (44.6 mV dec^?1) superior to previously reported graphene‐based materials, and even comparable to the state‐of‐the art Pt/C catalyst. X‐ray absorption near‐edge structure (XANES) and solid‐state NMR studies reveal that the distinct feature of its structure is dual graphitic‐N doping in a six‐membered carbon ring. Density functional theory (DFT) calculations show that the unique doped structure is beneficial for the activation of C?H bonds and to make the carbon atom bonded to two graphitic N atoms an active site for the HER.     

Electrochemical performance of grown layer of Ni(OH)2 on nickel foam and treatment with phosphide and selenide for efficient water splitting

Active nanocomposites synthesized by the electrochemical approach play a vital role in energy generation, conversion, and storage technologies. Recently, scientists began to explore the use of earth-rich transition metal-based materials to replace precious metal-based catalysts. Transition metals (TMs) based nickel (Ni) and their pnictides compounds such as phosphides and selenides exhibit good activity for hydrogen evaluation reaction (HER) and the entire water electrolysis process. In this study, we first prepared Ni(OH)₂ and grown its layer on Ni foam (NF) and treated it with selenide (Se) and phosphide (P) then nickel-based selenide-phosphide catalyst (Ni–P–Se) was prepared by simultaneous selenization and phosphidation process for the first time. The as-obtained composite was then analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), elemental mapping and transmission electron microscope (TEM) means to study the composition, structure, and micro-morphology of materials. Furthermore, we also observed electrocatalytic water splitting activity using electrochemical cell. The results of electrochemical tests depicted that the selenization and phosphidation treatments significantly enhanced the electrocatalytic HER activity of the starting materials. The overpotentials required for Ni–P–Se to reach 10 ?mA ?cm^?2 and 100 ?mA ?cm^?2 were only 242 ?mV and 282 ?mV. The Tafel slope of Ni–P–Se is 151 ?mV dec^?1, which is lower than that of nickel phosphide, selenide, and hydroxide indicating that selenide-phosphide enhances the HER reaction kinetics of the material, which in turn increases hydrogen output rate as compared with previous studies.     

Hollow Chevrel‐Phase NiMo3S4 for Hydrogen Evolution in Alkaline Electrolytes

Electrochemical water splitting to generate molecular hydrogen requires catalysts that are cheap, active, and stable, particularly for alkaline electrolyzers, where the cathodic hydrogen evolution reaction is slower in base than in acid even on platinum. Herein, we describe the synthesis of new hollow Chevrel‐phase NiMo₃S₄ and its alkaline hydrogen evolution reaction (HER) performance: onset potential of ?59 mV, Tafel slope of 98 mV per decade, and exchange current density of 3.9×10^?2 mA cm^?2. This Chevrel‐phase chalcogenide also demonstrates outstanding long‐term stability under harsh HER cycling conditions. Chevrel‐phase nanomaterials show promise as efficient, low‐cost catalysts for alkaline electrolyzers.     

Devisable POM/Ni Foam Composite: Precisely Control Synthesis toward Enhanced Hydrogen Evolution Reaction at High pH

Polyoxometalates (POMs) are promising catalysts for the electrochemical hydrogen production from water owing to their high intrinsic catalytic activity and chemical tunability. However, poor electrical conductivity and easy detachment of the POMs from the electrode cause significant challenges under operating condition. Herein, a simple one-step hydrothermal method is reported to synthesize a series of Dexter–Silverton POM/Ni foam composites (denoted as Ni M -POM/Ni; M =Co, Zn, Mn), in which the stable linkage between the POM catalysts and the Ni foam electrodes lead to high activity for the hydrogen evolution reaction (HER). Among them, the highest HER performance can be observed in the NiCo-POM/Ni, featuring an overpotential of 64 mV (at 10 mA cm⁻², vs. reversible hydrogen electrode), and a Tafel slope of 75 mV dec⁻¹ in 1.0 m aqueous KOH. Moreover, the NiCo-POM/Ni catalyst showed a high faradaic efficiency ≈97 % for HER. Post-catalytic of NiCo-POM/Ni analyses showed virtually no mechanical or chemical degradation. The findings propose a facile and inexpensive method to design stable and effective POM-based catalysts for HER in alkaline water electrolysis.     

Enhanced Electron Penetration through an Ultrathin Graphene Layer for Highly Efficient Catalysis of the Hydrogen Evolution Reaction

Major challenges encountered when trying to replace precious‐metal‐based electrocatalysts of the hydrogen evolution reaction (HER) in acidic media are related to the low efficiency and stability of non‐precious‐metal compounds. Therefore, new concepts and strategies have to be devised to develop electrocatalysts that are based on earth‐abundant materials. Herein, we report a hierarchical architecture that consists of ultrathin graphene shells (only 1–3 layers) that encapsulate a uniform CoNi nanoalloy to enhance its HER performance in acidic media. The optimized catalyst exhibits high stability and activity with an onset overpotential of almost zero versus the reversible hydrogen electrode (RHE) and an overpotential of only 142 mV at 10 mA cm^?2, which is quite close to that of commercial 40 % Pt/C catalysts. Density functional theory (DFT) calculations indicate that the ultrathin graphene shells strongly promote electron penetration from the CoNi nanoalloy to the graphene surface. With nitrogen dopants, they synergistically increase the electron density on the graphene surface, which results in superior HER activity on the graphene shells.     

Phosphorus‐Modified Tungsten Nitride/Reduced Graphene Oxide as a High‐Performance,Non‐Noble‐Metal Electrocatalyst for the Hydrogen Evolution Reaction

Phosphorus‐modified tungsten nitride/reduced graphene oxide (P‐WN/rGO) is designed as a high‐efficient, low‐cost electrocatalyst for the hydrogen evolution reaction (HER). WN (ca. 3 nm in size) on rGO is first synthesized by using the H₃[PO₄(W₃O₉)₄] cluster as a W source. Followed by phosphorization, the particle size increase slightly to about 4 nm with a P content of 2.52 at %. The interaction of P with rGO and WN results in an obvious increase of work function, being close to Pt metal. The P‐WN/rGO exhibits low onset overpotential of 46 mV, Tafel slope of 54 mV dec⁻¹, and a large exchange current density of 0.35 mA cm⁻² in acid media. It requires overpotential of only 85 mV at current density of 10 mA cm⁻², while remaining good stability in accelerated durability testing. This work shows that the modification with a second anion is powerful way to design new catalysts for HER.     

Flower-like Fe-Co-M (M=S,O, P and Se) Nanosheet Arrays Grown on Nickel Foam as High-efficiency Bifunctional Electrocatalysts

The development of highly efficient, inexpensive, abundant and non-precious metal electrocatalysts is the lifeblood of the hydrogen production industry, especially the hydrogen production industry by electrolysis of water. A Fe-Co-S/NF bifunctional electrocatalyst with nanoflower-like structure was synthesized on three-dimensional porous nickel foam through one-step hydrothermal and one-step high-temperature sulfuration operations, and the material displays high-efficiency electrocatalytic performance. As a catalyst for the hydrogen evolution reaction, Fe-Co-S/NF can drive a current density of 10 mA/cm² at an overpotential of 143 mV with a Tafel slope of 80.2 mV/dec. When it was used as an oxygen evolution reaction catalyst, it exhibits good OER reactivity with a low Tafel slope (82.6 mV/dec) and with requiring only 117 mV overpotential to drive current densities up to 50 mA/cm². In addition, the Fe-Co-S/NF//Fe-Co-S/NF electrolytic cell was assembled, an electrolysis voltage of 1.64 V is required to drive a current density of 50 mA/cm², which is one of the most active catalysts reported so far. This work indicates that the introduction of S, P and Se treating processes could effectively improve electrical conductivity of the material and enhance the catalytic activity of the material. This work offers an effective and convenient method for improving the morphology of the catalyst, increasing the surface area of the catalyst and developing high-efficiency and low-cost catalysts.     

Efficient and Robust Hydrogen Evolution: Phosphorus Nitride Imide Nanotubes as Supports for Anchoring Single Ruthenium Sites

Amorphous phosphorus nitride imide nanotubes (HPN) are reported as a novel substrate to stabilize materials containing single‐metal sites. Abundant dangling unsaturated P vacancies play a role in stabilization. Ruthenium single atoms (SAs) are successfully anchored by strong coordination interactions between the d orbitals of Ru and the lone pair electrons of N located in the HPN matrix. The atomic dispersion of Ru atoms can be distinguished by X‐ray absorption fine structure measurements and spherical aberration correction electron microscopy. Importantly, Ru SAs@PN is an excellent electrocatalyst for the hydrogen evolution reaction (HER) in 0.5 m H₂SO₄, delivering a low overpotential of 24 mV at 10 mA cm^?2 and a Tafel slope of 38 mV dec^?1. The catalyst exhibits robust stability in a constant current test at a large current density of 162 mA cm^?2 for more than 24 hours, and is operative for 5000 cycles in a cyclic voltammetry test. Additionally, Ru SAs@PN presents a turnover frequency (TOF) of 1.67 H₂ s^?1 at 25 mV, and 4.29 H₂ s^?1 at 50 mV, in 0.5 m H₂SO₄ solution, outperforming most of the reported hydrogen evolution catalysts. Density functional theory (DFT) calculations further demonstrate that the Gibbs free energy of adsorbed H* over the Ru SAs on PN is much closer to zero compared with the Ru/C and Ru SAs supported on carbon and C₃N₄, thus considerably facilitating the overall HER performance.     

Heterostructured Inter-Doped Ruthenium–Cobalt Oxide Hollow Nanosheet Arrays for Highly Efficient Overall Water Splitting

The development of transition-metal-oxides (TMOs)-based bifunctional catalysts toward efficient overall water splitting through delicate control of composition and structure is a challenging task. Herein, the rational design and controllable fabrication of unique heterostructured inter-doped ruthenium–cobalt oxide [(Ru–Co)O_x] hollow nanosheet arrays on carbon cloth is reported. Benefiting from the desirable compositional and structural advantages of more exposed active sites, optimized electronic structure, and interfacial synergy effect, the (Ru–Co)O_x nanoarrays exhibited outstanding performance as a bifunctional catalyst. Particularly, the catalyst showed a remarkable hydrogen evolution reaction (HER) activity with an overpotential of 44.1 mV at 10 mA cm⁻² and a small Tafel slope of 23.5 mV dec⁻¹, as well as an excellent oxygen evolution reaction (OER) activity with an overpotential of 171.2 mV at 10 mA cm⁻². As a result, a very low cell voltage of 1.488 V was needed at 10 mA cm⁻² for alkaline overall water splitting.     

Fast Modulation of d-Band Holes Quantity in the Early Reaction Stages for Boosting Acidic Oxygen Evolution

Synthesis of highly active and durable oxygen evolution reaction (OER) catalysts applied in acidic water electrolysis remains a grand challenge. Here, we construct a type of high-loading iridium single atom catalysts with tunable d-band holes character (h-HL−Ir SACs, ∼17.2 wt % Ir) realized in the early OER operation stages. The in situ X-ray absorption spectroscopy reveals that the quantity of the d-band holes of Ir active sites can be fast increased by 0.56 unit from the open circuit to a low working potential of 1.35 V. More remarkably, in situ synchrotron infrared and Raman spectroscopies demonstrate the quick accumulation of *OOH and *OH intermediates over holes-modulated Ir sites in the early reaction voltages, achieving a rapid OER kinetics. As a result, this well-designed h-HL−Ir SACs exhibits superior performance for acidic OER with overpotentials of 216 mV @10 mA cm⁻² and 259 mV @100 mA cm⁻², corresponding to a small Tafel slope of 43 mV dec⁻¹. The activity of catalyst shows no evident attenuation after 60 h operation in acidic environment. This work provides some useful hints for the design of superior acidic OER catalysts.     

Coupling of Bifunctional CoMn‐Layered Double Hydroxide@Graphitic C3N4 Nanohybrids towards Efficient Photoelectrochemical Overall Water Splitting

The development of durable, low‐cost, and efficient photo‐/electrolysis for the oxygen and hydrogen evolution reactions (OER and HER) is important to fulfill increasing energy requirements. Herein, highly efficient and active photo‐/electrochemical catalysts, that is, CoMn‐LDH@g‐C₃N₄ hybrids, have been synthesized successfully through a facile in situ co‐precipitation method at room temperature. The CoMn‐LDH@g‐C₃N₄ composite exhibits an obvious OER electrocatalytic performance with a current density of 40 mA cm^?2 at an overpotential of 350 mV for water oxidation, which is 2.5 times higher than pure CoMn‐LDH nanosheets. For HER, CoMn‐LDH@g‐C₃N₄ (η₅₀=?448 mV) requires a potential close to Pt/C (η₅₀=?416 mV) to reach a current density of 50 mA cm². Furthermore, under visible‐light irradiation, the photocurrent density of the CoMn‐LDH@g‐C₃N₄ composite is 0.227 mA cm^?2, which is 2.1 and 3.8 time higher than pristine CoMn‐LDH (0.108 mA cm^?2) and g‐C₃N₄ (0.061 mA cm^?2), respectively. The CoMn‐LDH@g‐C₃N₄ composite delivers a current density of 10 mA cm^?2 at 1.56 V and 100 mA cm^?2 at 1.82 V for the overall water‐splitting reaction. Therefore, this work establishes the first example of pure CoMn‐LDH and CoMn‐LDH@g‐C₃N₄ hybrids as electrochemical and photoelectrochemical water‐splitting systems for both OER and HER, which may open a pathway to develop and explore other LDH and g‐C₃N₄ nanosheets as efficient catalysts for renewable energy applications.     

Phosphorus Vacancies that Boost Electrocatalytic Hydrogen Evolution by Two Orders of Magnitude

Vacancy engineering is an effective strategy to manipulate the electronic structure of electrocatalysts to improve their performance, but few reports focus on phosphorus vacancies (Pv). Herein, the creation of Pv in metal phosphides and investigation of their role in alkaline electrocatalytic hydrogen evolution reaction (HER) is presented. The Pv‐modified catalyst requires a minimum onset potential of 0 mV vs. RHE, a small overpotential of 27.7 mV to achieve 10 mA cm^?2 geometric current density and a Tafel slope of 30.88 mV dec^?1, even outperforms the Pt/C benchmark (32.7 mV@10 mA cm^?2 and 30.90 mV dec^?1). This catalyst also displays superior stability up to 504 hours without any decay. Experimental analysis and density functional theory calculations suggest Pv can weaken the hybridization of Ni 3d and P 2p orbitals, enrich the electron density of Ni and P atoms nearby Pv, and facilitate H* desorption process, contributing to outstanding HER activity and facile kinetics.     

Strong‐Coupled Cobalt Borate Nanosheets/Graphene Hybrid as Electrocatalyst for Water Oxidation Under Both Alkaline and Neutral Conditions

Developing highly active catalysts for the oxygen evolution reaction (OER) is of paramount importance for designing various renewable energy storage and conversion devices. Herein, we report the synthesis of a category of Co‐Pi analogue, namely cobalt‐based borate (Co‐B_i) ultrathin nanosheets/graphene hybrid by a room‐temperature synthesis approach. Benefiting from the high surface active sites exposure yield, enhanced electron transfer capacity, and strong synergetic coupled effect, this Co‐B_i NS/G hybrid shows high catalytic activity with current density of 10 mA cm^?2 at overpotential of 290 mV and Tafel slope of 53 mV dec^?1 in alkaline medium. Moreover, Co‐B_i NS/G electrocatalysts also exhibit promising performance under neutral conditions, with a low onset potential of 235 mV and high current density of 14.4 mA cm^?2 at 1.8 V, which is the best OER performance among well‐developed Co‐based OER electrocatalysts to date. Our finding paves a way to develop highly active OER electrocatalysts.