Fe-Doped CoP Nanoarray: A Monolithic Multifunctional Catalyst for Highly Efficient Hydrogen Generation

Controllable Surface Reorganization Engineering on Cobalt Phosphide Nanowire Arrays for Efficient Alkaline Hydrogen Evolution Reaction

Developing highly efficient hydrogen evolution reaction (HER) catalysts in alkaline media is considered significant and valuable for water splitting. Herein, it is demonstrated that surface reorganization engineering by oxygen plasma engraving on electocatalysts successfully realizes a dramatically enhanced alkaline HER activity. Taking CoP nanowire arrays grown on carbon cloth (denoted as CoP NWs/CC) as an example, the oxygen plasma engraving can trigger moderate CoO_x species formation on the surface of the CoP NWs/CC, which is visually verified by the X-ray absorption fine structure, high-resolution transmission electron microscopy, and energy-dispersive spectrometer (EDS) mapping. Benefiting from the moderate CoO_x species formed on the surface, which can promote the water dissociation in alkaline HER, the surface reorganization of the CoP NWs/CC realizes almost fourfold enhanced alkaline HER activity and a 180 mV decreased overpotential at 100 mA cm^-2 , compared with the pristine ones. More interestingly, this surface reorganization strategy by oxygen plasma engraving can also be effective to other electrocatalysts such as free-standing CoP, Co₄ N, O-CoSe₂ , and C-CoSe₂ nanowires, which verifies the universality of the strategy. This work thus opens up new avenues for designing alkaline HER electrocatalysts based on oxygen plasma engraving.

Controlled synthesis of Co3O4@NiMoO4 core–shell nanorod arrays for efficient water splitting

We reported for the first time the development of Co₃O₄@NiMoO₄ nanorod arrays on nickel foam (Co₃O₄@NiMoO₄/NF) as a robust Earth-abundant electrocatalyst for water splitting.

Fe-doped CoP nanosheet arrays: an efficient bifunctional catalyst for zinc–air batteries

Fe-doped CoP nanoarrays on nickel foam (Fe_0.33–CoP/NF) act as a superior bifunctional electrocatalyst to CoP/NF for both the OER and ORR in alkaline media. In concentrated alkaline media, zinc–air batteries based on Fe_0.33–CoP/NF exhibit a power density of 63 mW cm⁻² with a long cycle life (up to 200 h).

Amorphous Y(OH)3-promoted Ru/Y(OH)3 nanohybrids with high durability for electrocatalytic hydrogen evolution in alkaline media

A novel Ru/Y(OH)₃ nanohybrid with high activity and excellent durability for electrocatalytic hydrogen evolution in alkaline media was developed.

Highly-active oxygen evolution electrocatalyzed by an Fe-doped NiCr2O4 nanoparticle film

An Fe-doped NiCr₂O₄ nanoparticle film on Ni foam (Fe–NiCr₂O₄/NF) acts as a durable water oxidation electrocatalyst with superior activity, needing an overpotential of 318 mV to drive 500 mA cm⁻² in 1.0 M KOH.

Al-Doped Ni2P nanosheet array: a superior and durable electrocatalyst for alkaline hydrogen evolution

Al-Ni₂P/TM exhibits superior catalytic HER performance, requiring an overpotential of 129 mV at 10 mA cm⁻² in 1.0 M KOH.

FeMoO4nanorod array: a highly active 3D anode for water oxidation under alkaline conditions

As a durable water oxidation electrocatalyst, an FeMoO₄nanorod array on nickel foam (FeMoO₄/NF) shows superior catalytic activity offering a geometrical catalytic current density of 50 mA cm⁻²at an overpotential of only 293 mV in 1.0 M KOH.

Tungsten nitride/carbide nanocomposite encapsulated in nitrogen-doped carbon shell as an effective and durable catalyst for hydrogen evolution reaction

In situ carbonized WO_X/aniline hybrid nanoparticles were prepared and used to obtain WN–W₂C nanocomposites encapsulated in nitrogen-doped carbon shell, which demonstrated excellent HER performance.

In situ grown Co3O4/Co(OH)2 hybrids as efficient electrocatalysts for water oxidation

A novel heterogeneous Co₃O₄/Co(OH)₂ hybrid is prepared using a controllable facile one-pot hydrothermal reaction. The as-obtained hierarchical Co₃O₄/Co(OH)₂ hybrids can serve as highly efficient electrocatalytic water oxidation catalysts for alkaline electrolytes.

In situ synthesis of NiSe@CoP core–shell nanowire arrays on nickel foam as a highly efficient and robust electrode for electrochemical hydrogen generation in both alkaline and acidic media

The efficient generation of hydrogen through the electro-splitting of water has attracted great attention.

Oriented CuCo2S4 nanograss arrays/Ni foam as an electrode for a high-performance all-solid-state supercapacitor

An oriented nanograss array consisting of CuCo₂S₄ nanocrystallines was directly prepared on Ni foam by a hydrothermal method. The uniform arrays with a single blade diameter of ∼100 nm and length of ∼4 μm can grow tightly on Ni foam without any binders. The ordered one-dimensional structure facilitates the electron transport to Ni substrates along the axial direction. The electrochemical properties were presented in three- and two-electrode configurations, demonstrating an enhanced specific capacitance and a long-term cycling stability. As a practical all-solid-state device, it achieved a high energy density of 31.88 W h kg^-1 at a power density of 3.20 kW kg^-1. Even at a higher power density of 15.23 W h kg^-1, the device still had an energy density of 16.5 kW kg^-1. After 5000 cycles, the retention ratio was higher than 99% at high current density of 11.36 A g^-1.

A Ni(OH)2-CoS2 hybrid nanowire array: a superior non-noble-metal catalyst toward the hydrogen evolution reaction in alkaline media

The rising H₂ economy urgently demands active, durable and cost-effective catalysts for the electrochemical hydrogen evolution reaction (HER). However, improving the HER performance of electrocatalysts in alkaline media is still challenging. Herein, we report the development of a nickel hydroxide-cobalt disulfide nanowire array on a carbon cloth (Ni(OH)₂-CoS₂/CC) as a hybrid catalyst to significantly enhance the HER activity in alkaline solutions. Benefitting from heterogeneous interfaces in this 3D hybrid electrocatalyst, Ni(OH)₂-CoS₂/CC shows superior HER activity with only 99 mV overpotential to drive a current density of 20 mA cm^-2 in 1.0 M KOH, which is 100 mV less than that of CoS₂/CC. Moreover, Ni(OH)₂-CoS₂/CC exhibits long-term electrochemical durability with the maintenance of its catalytic activity for 30 h. Density functional theory calculations are performed to gain further insight into the effect of Ni(OH)₂-CoS₂ interfaces, revealing that Ni(OH)₂ plays a key role in water dissociation to hydrogen intermediates and CoS₂ facilitates the adsorption of hydrogen intermediates and H₂ generation. This work not only develops a promising electrocatalyst for the alkaline HER, but also paves a way to enhance the alkaline HER activity of CoS₂via the interface engineering strategy.

Mo doped Ni2P nanowire arrays: an efficient electrocatalyst for the hydrogen evolution reaction with enhanced activity at all pH values

We report the successful synthesis of Mo doped Ni₂P nanowires (NWs) on a Ni foam (NF) substrate by a two-step strategy, which could be used as an efficient and stable hydrogen evolution reaction (HER) electrocatalyst over the whole pH range (0-14). Electrochemical investigations demonstrated that Mo doping made the catalytic activity of Ni₂P significantly enhanced. To achieve a current density of 10 mA cm^-2, Mo-Ni₂P NWs/NF required an overpotential of 67 mV in acidic solution, 78 mV in alkaline solution and 84 mV in neutral solution. It also showed superior stability with negligible activity decay after its use in the HER under different pH conditions for 24 h. Such excellent HER activity might originate from the synergistic effect between molybdenum (Mo) and nickel (Ni) atoms. The present work provides a valuable route for the design and synthesis of inexpensive and efficient all-pH HER electrocatalysts.

Self-Templated Fabrication of MoNi4 /MoO3-x Nanorod Arrays with Dual Active Components for Highly Efficient Hydrogen Evolution

A binder-free efficient MoNi₄ /MoO_3-x nanorod array electrode with 3D open structure is developed by using Ni foam as both scaffold and Ni source to form NiMoO₄ precursor, followed by subsequent annealing in a reduction atmosphere. It is discovered that the self-templated conversion of NiMoO₄ into MoNi₄ nanocrystals and MoO_3-x as dual active components dramatically boosts the hydrogen evolution reaction (HER) performance. Benefiting from high intrinsic activity, high electrochemical surface area, 3D open network, and improved electron transport, the resulting MoNi₄ /MoO_3-x electrode exhibits a remarkable HER activity with extremely low overpotentials of 17 mV at 10 mA cm^-2 and 114 mV at 500 mA cm^-2 , as well as a superior durability in alkaline medium. The water-alkali electrolyzer using MoNi₄ /MoO_3-x as cathode achieves stable overall water splitting with a small cell voltage of 1.6 V at 30 mA cm^-2 . These findings may inspire the exploration of cost-effective and efficient electrodes by in situ integrating multiple highly active components on 3D platform with open conductive network for practical hydrogen production.

Metallic Transition Metal Selenide Holey Nanosheets for Efficient Oxygen Evolution Electrocatalysis

Catalysts for oxygen evolution reaction (OER) are pivotal to the scalable storage of sustainable energy by means of converting water to oxygen and hydrogen fuel. Designing efficient electrocatalysis combining the features of excellent electrical conductivity, abundant active surface, and structural stability remains a critical challenge. Here, we report the rational design and controlled synthesis of metallic transition metal selenide NiCo₂Se₄-based holey nanosheets as a highly efficient and robust OER electrocatalyst. Benefiting from synergistic effects of metallic nature, heteroatom doping, and holey nanoarchitecture, NiCo₂Se₄ holey nanosheets exhibit greatly enhanced kinetics and improved cycling stability for OER. When further employed as an alkaline electrolyzer, the NiCo₂Se₄ holey nanosheet electrocatalyst enables a high-performing overall water splitting with a low applied external potential of 1.68 V at 10 mA cm^-2. This work not only represents a promising strategy to design the efficient and robust OER catalysts but also provides fundamental insights into the structure-property-performance relationship of transition metal selenide-based electrocatalytic materials.

Homologous Catalysts Based on Fe-Doped CoP Nanoarrays for High-Performance Full Water Splitting under Benign Conditions

The design and development of earth-abundant electrocatalysts for efficient full water splitting under mild conditions are highly desired, yet remain a challenging task. A homologous Fe-doped Co-based nanoarray incorporating complementary catalysts is shown to effect high-performance and durable water splitting in near-neutral media. Iron-doped cobalt phosphate borate nanoarray on carbon cloth (Fe-Co-Pi-Bi/CC) derived from iron-doped cobalt phosphide on CC (Fe-CoP/CC) through oxidative polarization behaves as a highly active bimetallic electrocatalyst for water oxidation with an overpotential of 382 mV to afford a catalytic current density of 10 mA cm^-2 in 0.1 m potassium borate (K-Bi, pH 9.2). Fe-CoP/CC is also highly active for the hydrogen evolution reaction, capable of driving 10 mA cm^-2 at an overpotential of only 175 mV in 0.1 m K-Bi. A two-electrode water electrolyzer incorporating Fe-Co-Pi-Bi/CC as anode and Fe-CoP/CC as cathode achieves 10 mA cm^-2 water-splitting current at a cell voltage of 1.95 V with strong long-term electrochemical durability.

Delocalized Spin States in 2D Atomic Layers Realizing Enhanced Electrocatalytic Oxygen Evolution

The electrocatalytic activity of transition-metal-based compounds is strongly related to the spin states of metal atoms. However, the ways for regulation of spin states of catalysts are still limited, and the underlying relationship between the spin states and catalytic activities remains unclear. Herein, for the first time, by taking Ni^II -based compounds without high or low spin states for example, it is shown that their spin states can be delocalized after introducing structural distortion to the atomic layers. The delocalized spin states for Ni atoms can provide not only high electrical conductivity but also low adsorption energy between the active sites and reaction intermediates for the system. As expected, the ultrathin nanosheets of nickel-chalcogenides with structural distortions show dramatically enhanced activity in electrocatalytic oxygen evolution compared to their corresponding bulk samples. This work establishes new way for the design of advanced electrocatalysts in transition-metal-based compounds via regulation of spin states.

In Situ Derived CoB Nanoarray: A High-Efficiency and Durable 3D Bifunctional Electrocatalyst for Overall Alkaline Water Splitting

The development of efficient bifunctional catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of extreme importance for future renewable energy systems. This Communication reports the recent finding that room-temperature treatment of CoO nanowire array on Ti mesh by NaBH₄ in alkaline media leads to in situ development of CoB nanoparticles on nanowire surface. The resulting self-supported CoB@CoO nanoarray behaves as a 3D bifunctional electrocatalyst with high activity and durability for both HER (<17% current density degradation after 20 h electrolysis) and OER (<14% current density degradation after 20 h electrolysis) with the need of the overpotentials of 102 and 290 mV to drive 50 mA cm^-2 in 1.0 m KOH, respectively. Moreover, its two-electrode alkaline water electrolyzer also shows remarkably high durability and only demands a cell voltage of 1.67 V to deliver 50 mA cm^-2 water-splitting current with a current density retention of 81% after 20 h electrolysis. This work provides a promising methodology for the designing and fabricating of metal-boride based nanoarray as a high-active water-splitting catalyst electrode for applications.

Porphyrinic Metal-Organic Framework-Templated Fe-Ni-P/Reduced Graphene Oxide for Efficient Electrocatalytic Oxygen Evolution

The sluggish kinetics of oxygen evolution reaction (OER) hampers the H₂ production by H₂O electrolysis, and it is very important for the development of highly efficient and low-priced OER catalysts. Herein, a representative metalloporphyrinic MOF, PCN-600-Ni, integrated with graphene oxide (GO), serves as an ideal precursor and template to afford bimetallic iron-nickel phosphide/reduced graphene oxide composite (denoted as Fe-Ni-P/rGO-T; T represents pyrolysis temperature) via pyrolysis and subsequent phosphidation process. Thanks to the highly porous structure, the synergetic effect of Fe and Ni elements in bimetallic phosphide, and the good conductivity endowed by rGO, the optimized Fe-Ni-P/rGO-400 exhibits remarkable OER activity in 1 M KOH solution, affording an extremely low overpotential of 240 mV at 10 mA/cm², which is far superior to the commercial IrO₂ and among the best in all non-noble metal-based electrocatalysts.

NiCo2 S4 Materials for Supercapacitor Applications

Cobalt-nickel sulfide (NiCo₂ S₄ ) shows extensive potential for innovative photoelectronic and energetic materials owing to distinctive physical and chemical properties. In this review, representative strategies for the fabrication and application of NiCo₂ S₄ and composite nanostructures are outlined for supercapacitors, with the aim of promoting the development of NiCo₂ S₄ and their composites in the supercapacitor field through an analysis and comparison of diverse nanostructures. A brief introduction into the structures, properties, and morphologies are presented. Further prospects and promising developments of the materials in the supercapacitor field are also proposed.

Au Promoted Nickel-Iron Layered Double Hydroxide Nanoarrays: A Modular Catalyst Enabling High-Performance Oxygen Evolution

Oxygen evolution reaction (OER) plays a key role in various energy conversion and storage technologies, such as water electrolysis, regenerative fuel cells, and rechargeable metal-air batteries. However, the slow kinetics of OER limit the performance and commercialization of such devices. Herein, we report on NiFe LDH@Au hybrid nanoarrays on Ni foam for much enhanced OER. By hybridization of electronegative Au and NiFe LDH with intrinsic remarkable OER catalytic activity, this modular electrode could drive an overall ultrahigh-performance and robust OER in base with the demand of overpotentials of only 221, 235, and 270 mV to afford 50, 100, and 500 mA cm^-2, respectively. Also, it exhibits superior catalytic activity and durability toward OER in 30 wt % KOH.

Electronic and Morphological Dual Modulation of Cobalt Carbonate Hydroxides by Mn Doping toward Highly Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting

Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co-Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized Co₁Mn₁CH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm^-2, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and stable current density of 1000 mA cm^-2 at only an overpotential of 462 mV with no interference from high-flux oxygen evolution. Despite no reports about effective HER on metal carbonate hydroxides yet, the small overpotential of 180 mV at 10 mA cm^-2 for HER can be also achieved on Co₁Mn₁CH/NF by the dual modulation of Mn doping. This offers a two-electrode electrolyzer using bifunctional Co₁Mn₁CH/NF as both anode and cathode to perform stable overall water splitting with a cell voltage of only 1.68 V at 10 mA cm^-2. These findings may open up opportunities to explore other multimetal carbonate hydroxides as practical bifunctional electrocatalysts for scale-up water electrolysis.

Efficient Electrocatalyst for the Hydrogen Evolution Reaction Derived from Polyoxotungstate/Polypyrrole/Graphene

Efficient hydrogen evolution reaction (HER) from water by electrocatalysis using cost-effective materials is critical to realize the clean hydrogen production. Herein, with controlling the structure and composition of polyoxotungstate/conductive polypyrrole/graphene (PCG) precursor precisely and followed by a temperature-programmed reaction, we developed a highly active and stable catalyst: NC@W_x C/NRGO (NC: nitrogen-doped porous carbon, NRGO: nitrogen-doped reduced graphene oxide). The composite presents splendid performance towards HER in acidic media, with a small onset overpotential of 24 mV versus RHE (reversible hydrogen electrode), a low Tafel slope of 58.4 mV dec^-1 , a low overpotential of 100 mV at 10 mA cm^-2 , and remarkable long-term cycle stability. This is one of the highest HER catalysts among the tungsten carbide-based materials ever reported.

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.

Three-Dimensional Cobalt Phosphide Nanowire Arrays as Negative Electrode Material for Flexible Solid-State Asymmetric Supercapacitors

Despite the great progress that has been accomplished in supercapacitors, the imbalance of the development of positive and negative electrode materials still remains a critical issue to achieve high energy density; therefore, exploring high-performance negative electrode materials is highly desirable. In this article, three-dimensional cobalt phosphide (CoP) nanowire arrays were synthesized on a carbon cloth and were utilized as a binder-free supercapacitor negative electrode. The as-synthesized CoP nanowire arrays presented a high capacitance of 571.3 mF/cm² at a current density of 1 mA/cm². By using CoP nanowire arrays as the negative electrode and MnO₂ nanowire arrays as the positive electrode, a flexible solid-state asymmetric supercapacitor has been fabricated and has exhibited excellent electrochemical performance, such as a high energy density of 0.69 mWh/cm³ and a high power density of 114.2 mW/cm³. In addition, the solid-state asymmetric supercapacitor shows high cycle stability with 82% capacitance retention after 5000 charge/discharge cycles. This work demonstrates that CoP is a promising negative electrode material for high-performance supercapacitor applications.

Large-Scale Synthesis of Carbon-Shell-Coated FeP Nanoparticles for Robust Hydrogen Evolution Reaction Electrocatalyst

A highly active and stable non-Pt electrocatalyst for hydrogen production has been pursued for a long time as an inexpensive alternative to Pt-based catalysts. Herein, we report a simple and effective approach to prepare high-performance iron phosphide (FeP) nanoparticle electrocatalysts using iron oxide nanoparticles as a precursor. A single-step heating procedure of polydopamine-coated iron oxide nanoparticles leads to both carbonization of polydopamine coating to the carbon shell and phosphidation of iron oxide to FeP, simultaneously. Carbon-shell-coated FeP nanoparticles show a low overpotential of 71 mV at 10 mA cm^-2, which is comparable to that of a commercial Pt catalyst, and remarkable long-term durability under acidic conditions for up to 10 000 cycles with negligible activity loss. The effect of carbon shell protection was investigated both theoretically and experimentally. A density functional theory reveals that deterioration of catalytic activity of FeP is caused by surface oxidation. Extended X-ray absorption fine structure analysis combined with electrochemical test shows that carbon shell coating prevents FeP nanoparticles from oxidation, making them highly stable under hydrogen evolution reaction operation conditions. Furthermore, we demonstrate that our synthetic method is suitable for mass production, which is highly desirable for large-scale hydrogen production.

Nickel-Cobalt Diselenide 3D Mesoporous Nanosheet Networks Supported on Ni Foam: An All-pH Highly Efficient Integrated Electrocatalyst for Hydrogen Evolution

Novel 3D Ni_1-x Co_x Se₂ mesoporous nanosheet networks with tunable stoichiometry are successfully synthesized on Ni foam (Ni_1-x Co_x Se₂ MNSN/NF with x ranging from 0 to 0.35). The collective effects of special morphological design and electronic structure engineering enable the integrated electrocatalyst to have very high activity for hydrogen evolution reaction (HER) and excellent stability in a wide pH range. Ni_0.89 Co_0.11 Se₂ MNSN/NF is revealed to exhibit an overpotential (η₁₀ ) of 85 mV at -10 mA cm^-2 in alkaline medium (pH 14) and η₁₀ of 52 mV in acidic solution (pH 0), which are the best among all selenide-based electrocatalysts reported thus far. In particular, it is shown for the first time that the catalyst can work efficiently in neutral solution (pH 7) with a record η₁₀ of 82 mV for all noble metal-free electrocatalysts ever reported. Based on theoretical calculations, it is further verified that the advanced all-pH HER activity of Ni_0.89 Co_0.11 Se₂ is originated from the enhanced adsorption of both H⁺ and H₂ O induced by the substitutional doping of cobalt at an optimal level. It is believed that the present work provides a valuable route for the design and synthesis of inexpensive and efficient all-pH HER electrocatalysts.

A TiO2/FeMnP Core/Shell Nanorod Array Photoanode for Efficient Photoelectrochemical Oxygen Evolution

A variety of catalysts have recently been developed for electrocatalytic oxygen evolution, but very few of them can be readily integrated with semiconducting light absorbers for photoelectrochemical or photocatalytic water splitting. Here, we demonstrate an efficient core/shell photoanode with a highly active oxygen evolution electrocatalyst shell (FeMnP) and semiconductor core (rutile TiO₂) for photoelectrochemical oxygen evolution reaction. Metal-organic chemical vapor deposition from a single-source precursor was used to ensure good contact between the FeMnP and the TiO₂. The TiO₂/FeMnP core/shell photoanode reaches the theoretical photocurrent density for rutile TiO₂ of 1.8 mA cm^-2 at 1.23 V vs reversible hydrogen electrode under simulated 100 mW cm^-2 (1 sun) irradiation. The dramatic enhancement is a result of the synergistic effects of the high oxygen evolution reaction activity of FeMnP (delivering an overpotential of 300 mV with a Tafel slope of 65 mV dec^-1 in 1 M KOH) and the conductive interlayer between the surface active sites and semiconductor core which boosts the interfacial charge transfer and photocarrier collection. The facile fabrication of the TiO₂/FeMnP core/shell nanorod array photoanode offers a compelling strategy for preparing highly efficient photoelectrochemical solar energy conversion devices.

Microwave-Initiated Facile Formation of Ni3Se4 Nanoassemblies for Enhanced and Stable Water Splitting in Neutral and Alkaline Media

Molecular hydrogen (H₂) generation through water splitting with minimum energy loss has become practically possible due to the recent evolution of high-performance electrocatalysts. In this study, we fabricated, evaluated, and presented such a high-performance catalyst which is the Ni₃Se₄ nanoassemblies that can efficiently catalyze water splitting in neutral and alkaline media. A hierarchical nanoassembly of Ni₃Se₄ was fabricated by functionalizing the surface-cleaned Ni foam using NaHSe solution as the Se source with the assistance of microwave irradiation (300 W) for 3 min followed by 5 h of aging at room temperature (RT). The fabricated Ni₃Se₄ nanoassemblies were subjected to catalyze water electrolysis in neutral and alkaline media. For a defined current density of 50 mA cm^-2, the Ni₃Se₄ nanoassemblies required very low overpotentials for the oxygen evolution reaction (OER), viz., 232, 244, and 321 mV at pH 14.5, 14.0, and 13.0 respectively. The associated lower Tafel slope values (33, 30, and 40 mV dec^-1) indicate the faster OER kinetics on Ni₃Se₄ surfaces in alkaline media. Similarly, in the hydrogen evolution reaction (HER), for a defined current density of 50 mA cm^-2, the Ni₃Se₄ nanoassemblies required low overpotentials of 211, 206, and 220 mV at pH 14.5, 14.0, and 13.0 respectively. The Tafel slopes for HER at pH 14.5, 14.0, and 13.0 are 165, 156, and 128 mV dec^-1, respectively. A comparative study on both OER and HER was carried out with the state-of-the-art RuO₂ and Pt under identical experimental conditions, the results of which revealed that our Ni₃Se₄ is a far better high-performance catalyst for water splitting. Besides, the efficiency of Ni₃Se₄ nanoassemblies in catalyzing water splitting in neutral solution was carried out, and the results are better than many previous reports. With these amazing advantages in fabrication method and in catalyzing water splitting at various pH, the Ni₃Se₄ nanoassemblies can be an efficient, cheaper, nonprecious, and high-performance electrode for water electrolysis with low overpotentials.

Phytic acid-derivative transition metal phosphides encapsulated in N,P-codoped carbon: an efficient and durable hydrogen evolution electrocatalyst in a wide pH range

Applications of highly-efficient and durable non-precious metal electrocatalysts for hydrogen evolution reaction (HER) have great potential to relieve the energy crisis. Here, we demonstrate a green method for fabrication of a number of transition metal phosphides (TMPs) by pyrolyzing melamine and self-assembled phytic acid (PA) cross-linked metal complexes. The obtained materials consisting of TMP nanoparticles (NPs) are encapsulated in N,P-codoped carbon (NPC). Among TMPs, the resultant FeP NPs encapsulated in the NPC matrix (FeP NPs@NPC) show the highest HER activity at all pH values. At a current density of 10 mA cm^-2, FeP NPs@NPC displays overpotentials of 130, 386 and 214 mV in 0.5 M H₂SO₄, 1.0 M phosphate buffer solution (PBS) and 1.0 M KOH, respectively. Additionally, the encapsulation by NPC effectively prevents FeP NPs from corrosion, exhibiting almost unfading catalytic activity after 10 h testing in acidic, neutral and basic electrolytes. More importantly, other TMPs wrapped in NPC (CoP NPs@NPC and Ni₂P NPs@NPC) can be easily obtained by this method, which also exhibit relatively high activity toward HER. Therefore, this generic synthesis strategy opens a door for unprecedented design and fabrication of novel low-cost TMP based electrocatalysts for HER and other electrochemical applications.

Dominating Role of Ni0 on the Interface of Ni/NiO for Enhanced Hydrogen Evolution Reaction

The research of a robust catalytic system based on single NiO_x electrocatalyst for hydrogen evolution reaction (HER) remains a huge challenge. Particularly, the factors that dominate the catalytic properties of NiO_x-based hybrids for HER have not been clearly demonstrated. Herein, a convenient protocol for the fabrication of NiO_x@bamboo-like carbon nanotube hybrids (NiO_x@BCNTs) is designed. The hybrids exhibit superb catalytic ability and considerable durability in alkaline solution. A benchmark HER current density of 10 mA cm^-2 has been achieved at an overpotential of ∼79 mV. In combination with the experimental results and density functional theory (DFT) calculations, this for the first time definitely validates that the inherent high Ni⁰ ratio and the Ni⁰ on the interface of Ni/NiO play a vital role in the outstanding catalytic performance. Especially, the Ni⁰ on the interface of Ni/NiO performs superior activity for water splitting compared with that of bulk Ni⁰. These conclusions provide guidance for the rational design of the future non-noble metallic catalysts.

Nonprecious metal phosphides as catalysts for hydrogen evolution, oxygen reduction and evolution reactions

Inexpensive nonprecious metal phosphides have been extensively investigated as catalysts over the past few years.