Promoting Active Sites in Core–Shell Nanowire Array as Mott–Schottky Electrocatalysts for Efficient and Stable Overall Water Splitting

Developing earth‐abundant, active, and robust electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains a vital challenge for efficient conversion of sustainable energy sources. Herein, metal–semiconductor hybrids are reported with metallic nanoalloys on various defective oxide nanowire arrays (Cu/CuO_x, Co/CoO_x, and CuCo/CuCoO_x) as typical Mott–Schottky electrocatalysts. To build the highway of continuous electron transport between metals and semiconductors, nitrogen‐doped carbon (NC) has been implanted on metal–semiconductor nanowire array as core–shell conductive architecture. As expected, NC/CuCo/CuCoO_x nanowires arrays, as integrated Mott–Schottky electrocatalysts, present an overpotential of 112 mV at 10 mA cm^?2 and a low Tafel slope of 55 mV dec^?1 for HER, simultaneously delivering an overpotential of 190 mV at 10 mA cm^?2 for OER. Most importantly, NC/CuCo/CuCoO_x architectures, as both the anode and the cathode for overall water splitting, exhibit a current density of 10 mA cm^?2 at a cell voltage of 1.53 V with excellent stability due to high conductivity, large active surface area, abundant active sites, and the continuous electron transport from prominent synergetic effect among metal, semiconductor, and nitrogen‐doped carbon. This work represents an avenue to design and develop efficient and stable Mott–Schottky bifunctional electrocatalysts for promising energy conversion.     

Overall Water Splitting Catalyzed Efficiently by an Ultrathin Nanosheet‐Built,Hollow Ni3S2‐Based Electrocatalyst

Making highly efficient catalysts for an overall ?water splitting reaction is vitally important to bring solar/electrical‐to‐hydrogen energy conversion processes into reality. Herein, the synthesis of ultrathin nanosheet‐based, hollow MoO_x/Ni₃S₂ composite microsphere catalysts on nickel foam, using ammonium molybdate as a precursor and the triblock copolymer pluronic P123 as a structure‐directing agent is reported. It is also shown that the resulting materials can serve as bifunctional, non‐noble metal electrocatalysts with high activity and stability for the hydrogen evolution reaction (HER) as well as the oxygen evolution reaction (OER). Thanks to their unique structural features, the materials give an impressive water‐splitting current density of 10 mA cm^?2 at ≈1.45 V with remarkable durability for >100 h when used as catalysts both at the cathode and the anode sides of an alkaline electrolyzer. This performance for an overall water splitting reaction is better than even those obtained with an electrolyzer consisting of noble metal‐based Pt/C and IrO_x/C catalytic couple—the benchmark catalysts for HER and OER, respectively.     

Vertically Aligned WS2 Nanosheets for Water Splitting

Vertically aligned WS₂ (VAWS₂) nanosheet films are prepared using a lithium based anodization electrolyte to fabricate WO₃ films followed by sulfurization. The VAWS₂ synthesized here is self‐organized as a conformal structure to expose active edge sites for water splitting. These vertically aligned nanosheets are composed of exfoliated WS₂ to provide abundant active edges for catalytic reactions. Hydrogen evolution activity of the VAWS₂ is demonstrated to show high catalytic current, low onset overpotential and small Tafel slope. By certain measures, this VAWS₂ nanosheet film outperforms some of the state‐of‐the‐art hydrogen evolution reaction (HER) catalysts, which opens up a new pathway to simply and scalably fabricate high‐performance water electrolysis catalysts.     

Engineering an Earth‐Abundant Element‐Based Bifunctional Electrocatalyst for Highly Efficient and Durable Overall Water Splitting

The simultaneous and efficient evolution of hydrogen and oxygen with earth‐abundant, highly active, and robust bifunctional electrocatalysts is a significant concern in water splitting. Herein, non‐noble metal‐based Ni–Co–S bifunctional catalysts with tunable stoichiometry and morphology are realized. The engineering of electronic structure and subsequent morphological design synergistically contributes to significantly elevated electrocatalytic performance. Stable overpotentials (η₁₀) of 243 mV (vs reversible hydrogen electrode) for oxygen evolution reaction (OER) and 80 mV for hydrogen evolution reaction (HER), as well as Tafel slopes of 54.9 mV dec^?1 for OER and 58.5 mV dec^?1 for HER, are demonstrated. In addition, density functional theory calculations are performed to determine the optimal electronic structure via the electron density differences to verify the enhanced OER activity is related to the Co top site on the (110) surface. Moreover, the tandem bifunctional NiCo₂S₄ exhibit a required voltage of 1.58 V (J = 10 mA cm^?2) for simultaneous OER and HER, and no obvious performance decay is observed after 72 h. When integrated with a GaAs solar cell, the resulting photoassisted water splitting electrolyzer shows a certified solar‐to‐hydrogen efficiency of up to 18.01%, further demonstrating the feasibility of engineering protocols and the promising potential of bifunctional NiCo₂S₄ for large‐scale overall water splitting.     

Fabrication and Shell Optimization of Synergistic TiO2‐MoO3 Core–Shell Nanowire Array Anode for High Energy and Power Density Lithium‐Ion Batteries

A novel synergistic TiO₂‐MoO₃ (TO‐MO) core–shell nanowire array anode has been fabricated via a facile hydrothermal method followed by a subsequent controllable electrodeposition process. The nano‐MoO₃ shell provides large specific capacity as well as good electrical conductivity for fast charge transfer, while the highly electrochemically stable TiO₂ nanowire core (negligible volume change during Li insertion/desertion) remedies the cycling instability of MoO₃ shell and its array further provides a 3D scaffold for large amount electrodeposition of MoO₃. In combination of the unique electrochemical attributes of nanostructure arrays, the optimized TO‐MO hybrid anode (mass ratio: ca. 1:1) simultaneously exhibits high gravimetric capacity (ca. 670 mAh g^?1; approaching the hybrid's theoretical value), excellent cyclability (>200 cycles) and good rate capability (up to 2000 mA g^?1). The areal capacity is also as high as 3.986 mAh cm^?2, comparable to that of typical commercial LIBs. Furthermore, the hybrid anode was assembled for the first time with commercial LiCoO₂ cathode into a Li ion full cell, which shows outstanding performance with maximum power density of 1086 W kg_total ^?1 (based on the total mass of the TO‐MO and LiCoO₂) and excellent energy density (285 Wh kg_total ^?1) that is higher than many previously reported metal oxide anode‐based Li full cells.     

Self‐Templated Fabrication of CoO–MoO2 Nanocages for Enhanced Oxygen Evolution

Oxygen evolution reaction (OER) plays a key role in energy conversion and storage processes such as water splitting and carbon dioxide reduction. However, the sluggish kinetics caused by insufficient active surface and limited charge transfer hinder OER's wide applications. In this work, a novel self‐templating strategy for the fabrication of composite CoO–MoO₂ nanocages with enhanced OER performance is proposed. By designing a nanocage structure and incorporating conductive MoO₂ to promote both mass and charge transfer, high OER activity (η = 312 mV at 10 mA cm^?2) as well as good stability in the resulting CoO–MoO₂ composite nanostructure can be achieved. This versatile synthetic strategy can also be extended to other metals (such as W) to provide greater opportunities for the controlled fabrication of mixed metal oxide nanostructures for electrochemical applications.     

Hollow Spherical Nanoshell Arrays of 2D Layered Semiconductor for High‐Performance Photodetector Device

Well‐defined hollow spherical nanoshell arrays of 2D transitional metal dichalcogenide (TMDC) nanomaterials for MoSe₂ and MoS₂ are grown via chemical vapor deposition technique for the first time. The hollow sphere arrays display the uniform dimensions of ≈450 nm with the shell thickness of ≈10 nm. The unique hollow sphere architecture with increased active surface area is forecasted to supply more efficient route to improve light‐harvesting efficiency through repeated light reflection and scattering inside the hollow structure without decay of response and recovery speed, because exceptional “SP–SP” junction barriers conducting mechanism can facilitate carriers tunneling and transport during the electron transfer procedure within the present particular structure. The MoSe₂ hollow sphere photodetector exhibits an outstanding responsivity (8.9 A W^?1), which is tenfold higher than that for MoSe₂ compact film (0.9 A W^?1), fast response and recovery speed, and good durability under illumination wavelength of 365 nm. Meanwhile, MoSe₂ hollow sphere arrays on flexible polyethylene terephthalate substrates reveal excellent bending stability. Therefore, this research indicates that unique hollow sphere architecture of 2D TMDC materials will be an anticipated avenue for efficient photodetector devices with far‐ranging capability.     

Nonprecious Intermetallic Al7Cu4Ni Nanocrystals Seamlessly Integrated in Freestanding Bimodal Nanoporous Copper for Efficient Hydrogen Evolution Catalysis

Tremendous demands for renewable hydrogen generated from water splitting have stimulated intensive research on developing earth‐abundant, non‐noble, and versatile metal catalysts toward the hydrogen evolution reactions (HER). Here, self‐supported Cu‐Ni‐Al hybrid electrodes that are composed of electroactive Al₇Cu₄Ni@Cu₄Ni core/shell nanocrystals seamlessly integrated in self‐supported 3D bimodal nanoporous Cu skeleton (Bi‐NP Cu/Al₇Cu₄Ni@Cu₄Ni) as robust HER electrocatalysts in alkaline electrolyte are reported. As a result of the proper architecture, in which the Bi‐NP Cu skeleton not only facilitates both electron and electrolyte transports but also provides high specific surface areas to fully use high electrocatalytic activity of Al₇Cu₄Ni@Cu₄Ni core/shell nanocrystals, the Bi‐NP Cu/Al₇Cu₄Ni@Cu₄Ni hybrid catalysts exhibit a low onset overpotential of 60 mV and a small Tafel slope of 110 mV dec^?1, enabling the catalytic current density of 10 mA cm^?2 at a low overpotential of 139 mV. The highly stable electrochemical performance makes them promising candidates as cathode catalysts in alkaline‐based devices.     

3D Self‐Supported Fe‐Doped Ni2P Nanosheet Arrays as Bifunctional Catalysts for Overall Water Splitting

The development of highly efficient bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial for improving the efficiency of overall water splitting, but still remains challenging issue. Herein, 3D self‐supported Fe‐doped Ni₂P nanosheet arrays are synthesized on Ni foam by hydrothermal method followed by in situ phosphorization, which serve as bifunctional electrocatalysts for overall water splitting. The as‐synthesized (Ni_0.33Fe_0.67)₂P with moderate Fe doping shows an outstanding OER performance, which only requires an overpotential of ≈230 mV to reach 50 mA cm^?2 and is more efficient than the other Fe incorporated Ni₂P electrodes. In addition, the (Ni_0.33Fe_0.67)₂P exhibits excellent activity toward HER with a small overpotential of ≈214 mV to reach 50 mA cm^?2. Furthermore, an alkaline electrolyzer is measured using (Ni_0.33Fe_0.67)₂P electrodes as cathode and anode, respectively, which requires cell voltage of 1.49 V to reach 10 mA cm^?2 as well as shows excellent stability with good nanoarray construction. Such good performance is attributed to the high intrinsic activity and superaerophobic surface property.     

A Novel MoSe2–Reduced Graphene Oxide/Polyimide Composite Film for Applications in Electrocatalysis and Photoelectrocatalysis Hydrogen Evolution

Promising catalytic activity of MoSe₂ in the hydrogen evolution reaction (HER) is synthesized on a new reduced graphene oxide/polyimide (rGO/PI) substrate by a simple electrochemical method. The MoSe₂ nanoparticles have excellent photo‐responsive properties; the potential difference could reach 0.45 V with the photo‐responsive time just 0.6 s. Furthermore, MoSe₂ thin film exhibits superior catalytic activity in the hydrogen evolution reaction (HER). It has a greater cathode current at more positive potential compared to other MoSe₂ and MoS₂, and the efficiency of H₂ evolution is strongly influenced by illumination; this suggests that MoSe₂ composite film has good photoelectrocatalysis properties for hydrogen evolution. Besides, both dark and illumination MoSe₂ films exhibit extremely high stability in acidic solution as the HER catalytic activity shows no degradation after 100 cycles for two hours. All results indicate that MoSe₂–rGO/PI composite film has potential to be a better catalyst for HER.     

Cobalt‐Doping in Molybdenum‐Carbide Nanowires Toward Efficient Electrocatalytic Hydrogen Evolution

Efficient hydrogen evolution reaction (HER) over noble‐metal‐free electrocatalysts provides one of the most promising pathways to face the energy crisis. Herein, facile cobalt‐doping based on Co‐modified MoO_x–amine precursors is developed to optimize the electrochemical HER over Mo₂C nanowires. The effective Co‐doping into Mo₂C crystal structure increases the electron density around Fermi level, resulting in the reduced strength of Mo–H for facilitated HER kinetics. As expected, the Co‐Mo₂C nanowires with an optimal Co/Mo ratio of 0.020 display a low overpotential (η₁₀ = 140 and 118 mV for reaching a current density of –10 mA cm^?2; η₁₀₀ = 200 and 195 mV for reaching a current density of –100 mA cm^?2), a small Tafel slope (39 and 44 mV dec^?1), and a low onset overpotential (40 and 25 mV) in 0.5 m H₂SO₄ and 1.0 m KOH, respectively. This work highlights a feasible strategy to explore efficient electrocatalysts via engineering on composition and nanostructure.     

Electronic and Vacancy Engineering of Mo–RuCoOx Nanoarrays for High-Efficiency Water Splitting (Adv. Funct. Mater. 40/2023)

Exploring efficient strategies to achieve novel high-efficiency catalysts for water splitting is of great significance to develop hydrogen energy technology. Herein, unique molybdenum (Mo)-doped ruthenium–cobalt oxide (Mo–RuCoO_x) nanosheet arrays are prepared as a high-performance bifunctional electrocatalyst toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through combining electronic and vacancy engineering. Theoretical calculations and experimental results reveal that the incorporation of Ru and Mo can effectively tune the electronic structure, and the controllable Mo dissolution coupling with the oxygen vacancy generation during surface reconstruction is able to optimize the adsorption energy of hydrogen/oxygen intermediates, thus greatly accelerating the kinetics for both HER and OER. As a result, the Mo–RuCoO_x nanoarrays exhibit remarkably low overpotentials of 41 and 156 mV at 10 mA cm⁻² for HER and OER in 1 m KOH, respectively. Furthermore, the two-electrode electrolyzer assembled by the Mo–RuCoO_x nanoarrays requires a cell voltage as low as 1.457 V to achieve 10 mA cm⁻² for alkaline overall water splitting. This work holds great promise to develop novel and highly active electrocatalysts for future energy conversion applications.     

Homologous CoP/NiCoP Heterostructure on N‐Doped Carbon for Highly Efficient and pH‐Universal Hydrogen Evolution Electrocatalysis

Hydrogen evolution electrocatalysts can achieve sustainable hydrogen production via electrocatalytic water splitting; however, designing highly active and stable noble‐metal‐free hydrogen evolution electrocatalysts that perform as efficiently as Pt catalysts over a wide pH range is a challenging task. Herein, a new 2D cobalt phosphide/nickelcobalt phosphide (CoP/NiCoP) hybrid nanosheet network is proposed, supported on an N‐doped carbon (NC) matrix as a highly efficient and durable pH‐universal hydrogen evolution reaction (HER) electrocatalyst. It is derived from topological transformation of corresponding layer double hydroxides and graphitic carbon nitride. This 2D CoP/NiCoP/NC catalyst exhibits versatile HER electroactivity with very low overpotentials of 75, 60, and 123 mV in 1 m KOH, 0.5 m H₂SO₄, and 1 m PBS electrolytes, respectively, delivering a current density of 10 mA cm^?2 for HER. Such impressive HER performance of the hybrid electrocatalyst is mainly attributed to the collective effects of electronic structure engineering, strong interfacial coupling between CoP and NiCoP in heterojunction, an enlarged surface area/exposed catalytic active sites due to the 2D morphology, and conductive NC support. This method is believed to provide a basis for the development of efficient 2D electrode materials with various electrochemical applications.     

Fe2O3 Nanoneedles on Ultrafine Nickel Nanotube Arrays as Efficient Anode for High‐Performance Asymmetric Supercapacitors

High performance of electrochemical energy storage devices depends on the smart structure engineering of electrodes, including the tailored nanoarchitectures of current collectors and subtle hybridization of active materials. To improve the anode supercapacitive performance of Fe₂O₃ for high‐voltage asymmetric supercapacitors, here, a hybrid core‐branch nanoarchitecture is proposed by integrating Fe₂O₃ nanoneedles on ultrafine Ni nanotube arrays (NiNTAs@Fe₂O₃ nanoneedles). The fabrication process employs a bottom‐up strategy via a modified template‐assisted method starting from ultrafine ZnO nanorod arrays, ensuring the formation of ultrafine Ni nanotube arrays with ultrathin tube walls. The novel developed NiNTAs@Fe₂O₃ nanoneedle electrode is demonstrated to be a highly capacitive anode (418.7 F g^?1 at 10 mV s^?1), matching well with the similarly built NiNTAs@MnO₂ nanosheet cathode. Contributed by the efficient electron collection paths and short ion diffusion paths in the uniquely designed anode and cathode, the asymmetric supercapacitors exhibit an excellent maximum energy density of 34.1 Wh kg^?1 at the power density of 3197.7 W kg^?1 in aqueous electrolyte and 32.2 Wh kg^?1 at the power density of 3199.5 W kg^?1 in quasi‐solid‐state gel electrolyte.     

Optical and Electrical Enhancement of Hydrogen Evolution by MoS2@MoO3 Core–Shell Nanowires with Designed Tunable Plasmon Resonance

The design of transition‐metal chalcogenides (TMCs) photocatalysts for water splitting is highly important, in which both light absorption and interfacial engineering play vital roles in photoexcited electron generation, electron transport, and ultimately speeding up water splitting. To this end, plasmonic metal nanomaterials with surface plasmon resonances are promising candidates. However, it is very difficult to enhance the light absorption and manage the interfacial engineering simultaneously, thus, resulting in suboptimal photocatalytic performance. Here, a doped semiconductor plasmon is proposed to optically and electrically enhance TMCs hydrogen evolution. With the tunability of plasmon resonance in a doped MoO₃ semiconductor via hydrogen reduction, the broadband absorption and good interfacial engineering are simultaneously demonstrated in flexible MoS₂@MoO₃ core–shell nanowire photocatalysts. Better energy‐band alignment with MoS₂ can also be realized, thereby achieving improved photoinduced electron generation. More importantly, the defects at the interface between MoO₃ and MoS₂ are effectively reduced because of precise tunability of plasmon resonance, which enhances electron transport. As a proof of concept, this optimized hybrid nanostructure exhibits outstanding H₂ evolution characteristics (841.4 μmol h^?1 g^?1), excellent stability, and good flexibility. The value is also one of the highest hydrogen evolution activity rates to date among the two dimensional‐layered visible‐light photocatalysts.     

Electrical Behavior and Electron Transfer Modulation of Nickel–Copper Nanoalloys Confined in Nickel–Copper Nitrides Nanowires Array Encapsulated in Nitrogen‐Doped Carbon Framework as Robust Bifunctional Electrocatalyst for Overall Water Splitting

Probing robust electrocatalysts for overall water splitting is vital in energy conversion. However, the catalytic efficiency of reported catalysts is still limited by few active sites, low conductivity, and/or discrete electron transport. Herein, bimetallic nickel–copper (NiCu) nanoalloys confined in mesoporous nickel–copper nitride (NiCuN) nanowires array encapsulated in nitrogen‐doped carbon (NC) framework (NC–NiCu–NiCuN) is constructed by carbonization‐/nitridation‐induced in situ growth strategies. The in situ coupling of NiCu nanoalloys, NiCuN, and carbon layers through dual modulation of electrical behavior and electron transfer is not only beneficial to continuous electron transfer throughout the whole system, but also promotes the enhancement of electrical conductivity and the accessibility of active sites. Owing to strong synergetic coupling effect, such NC–NiCu–NiCuN electrocatalyst exhibits the best hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance with a current density of 10 mA cm^?2 at low overpotentials of 93 mV for HER and 232 mV for OER, respectively. As expected, a two‐electrode cell using NC–NiCu–NiCuN is constructed to deliver 10 mA cm^?2 water‐splitting current at low cell voltage of 1.56 V with remarkable durability over 50 h. This work serves as a promising platform to explore the design and synthesis of robust bifunctional electrocatalyst for overall water splitting.     

Ru–Ru2PΦNPC and NPC@RuO2 Synthesized via Environment‐Friendly and Solid‐Phase Phosphating Process by Saccharomycetes as N/P Sources and Carbon Template for Overall Water Splitting in Acid Electrolyte

Although numerous ruthenium‐based phosphates possess high catalytic activities for hydrogen evolution reaction (HER), most of them rely on dangerous and toxic synthesis routes. Biological slices confirm that Ru ions can penetrate the cell walls of saccharomycete, which facilitates the adsorption of Ru ions. Herein, based on a green synthesis process by saccharomycete cells as the carbon template and nitrogen/phosphorus (N/P) sources, novel Janus‐like ruthenium–ruthenium phosphide nanoparticles embedded into a N/P dual‐doped carbon matrix (Ru–Ru₂PΦNPC) electrocatalyst for HER are synthesized. Electrochemical tests reveal that Ru–Ru₂PΦNPC displays remarkable performance with a low overpotential of 42 mV at 10 mA cm^?2 and demonstrates superior stability at a high current density in 0.5 m H₂SO₄. Furthermore, ruthenium oxide nanoparticles coated N/P dual‐doped carbon (NPC@RuO₂) are also synthesized with a yolk–shell structure using saccharomycete cells as the core template and RuO₂ as a shell to isolate saccharomycete cells from the oxidation reaction during calcination in air. The NPC@RuO₂ as oxygen evolution reaction electrocatalyst possesses a low overpotential of 220 mV at 10 mA cm^?2. Finally, the Ru–Ru₂PΦNPC is integrated as a cathode and NPC@RuO₂ is integrated as an anode to construct a two‐electrode electrolyzer to enable an excellent performance for overall water splitting with a cell voltage of 1.50 V at 10 mA cm^?2 in 0.5 m H₂SO₄.     

High‐Performance Overall CO2 Splitting on Hierarchical Structured Cobalt Disulfide with Partially Removed Sulfur Edges

The ability to develop bifunctional electrocatalysts for concurrent CO₂ reduction reaction (CO₂RR) and oxygen evolution reaction (OER) is the key to the practical application of CO₂ splitting to produce CO. However, this remains a grand challenge. Herein, a robust strategy to rationally craft hierarchical structured bifunctional electrocatalysts composed of 3D CoS₂ nanocages interconnected on 2D CoS₂ nanosheet arrays (denoted hierarchical CoS₂ nanocages) for high‐performance CO₂ splitting is developed. The subsequent calcination removes the partial S edges of CoS₂, thereby strongly suppressing the hydrogen evolution reaction (HER) of CoS₂. By combining theoretic and experimental results, for the first time, it is discovered that the plane S of CoS₂, instead of S edges, are highly active for CO₂RR but inactive for HER, rendering the plane S as ideal active sites for CO₂RR. Intriguingly, the composition tuning via calcination and the presence of a hierarchical architecture confer hierarchical CoS₂ nanocages respective outstanding CO₂RR and OER performance. Notably, the hierarchical CoS₂ nanocages can be exploited as bifunctional electrocatalysts for overall CO₂ splitting to yield the current density of 1 mA cm^?2 at a small cell voltage of 1.92 V, much lower than the widely reported values (>2.5 V).     

A Cobalt‐Based Amorphous Bifunctional Electrocatalysts for Water‐Splitting Evolved from a Single‐Source Lazulite Cobalt Phosphate

Over the years, cobalt phosphates (amorphous or crystalline) have been projected as one of the most significant and promising classes of nonprecious catalysts and studied exclusively for the electrocatalytic and photocatalytic oxygen evolution reaction (OER). However, their successful utilization of hydrogen evolution reaction (HER) and the reaction of overall water‐splitting is rather unexplored. Herein, presented is a crystalline cobalt phosphate, Co₃(OH)₂(HPO₄)₂, structurally related to the mineral lazulite, as an efficient precatalyst for OER, HER, and water electrolysis in alkaline media. During both electrochemical OER and HER, the Co₃(OH)₂(HPO₄)₂ nanostructure was completely transformed in situ into porous amorphous CoO_x (OH) films that mediate efficient OER and HER with extremely low overpotentials of only 182 and 87 mV, respectively, at a current density of 10 mA cm^?2. When assemble as anode and cathode in a two‐electrode alkaline electrolyzer, unceasing durability over 10 days is achieved with a final cell voltage of 1.54 V, which is superior to the recently reported effective bifunctional electrocatalysts. The strategy to achieve more active sites for oxygen and hydrogen generation via in situ oxidation or reduction from a well‐defined inorganic material provides an opportunity to develop cost‐effective and efficient electrocatalysts for renewable energy technologies.     

Mechanistic Insights on Ternary Ni2−xCoxP for Hydrogen Evolution and Their Hybrids with Graphene as Highly Efficient and Robust Catalysts for Overall Water Splitting

Searching the high‐efficient, stable, and earth‐abundant electrocatalysts to replace the precious noble metals holds the promise for practical utilizations of hydrogen and oxygen evolution reactions (HER and OER). Here, a series of highly active and robust Co‐doped nickel phosphides (Ni_2?xCo_xP) catalysts and their hybrids with reduced graphene oxide (rGO) are developed as bifunctional catalysts for both HER and OER. The Co‐doping in Ni₂P and their hybridization with rGO effectively regulate the catalytic activity of the surface active sites, accelerate the charge transfer, and boost their superior catalytic activity. Density functional theory calculations show that the Co‐doped catalysts deliver the moderate trapping of atomic hydrogen and facile desorption of the generated H₂ due to the H‐poisoned surface active sites of Ni_2?xCo_xP under the real catalytic process. Electrochemical measurements reveal the high HER efficiency and durability of the NiCoP/rGO hybrids in electrolytes with pH 0–14. Coupled with the remarkable and robust OER activity of the NiCoP/rGO hybrids, the practical utilization of the NiCoP/rGO‖NiCoP/rGO for overall water splitting yields a catalytic current density of 10 mA cm^?2 at 1.59 V over 75 h without an obvious degradation and Faradic efficiency of ≈100% in a two‐electrode configuration and 1.0 m KOH.