Plasmon‐Enhanced Photoelectrical Hydrogen Evolution on Monolayer MoS2 Decorated Cu1.75S‐Au Nanocrystals

Hydrogen production from water splitting through an efficient photoelectrochemical route requires photoinduced electron transfer from light harvesters to efficient electrocatalysts. Here, the plasmon‐enhanced photoelectrical nanocatalysts (NCs) have been successfully developed by coating a monolayer MoS₂ on the Cu_1.75S‐Au hetero‐nanoparticle for hydrogen evolution reaction (HER). The plasmonic NCs dramatically improve the HER, leading to 29.5‐fold increase of current under 650 nm excitation (1.0 W cm^?2). These NCs generate an exceptionally high current density of 200 mA cm^?2 at overpotential of 182.8 mV with a Tafel slope of 39 mV per decade and excellent stability, which is better than or comparable to the Pt‐free catalysts with carbon rod as counter electrode. The enhanced HER performance can be attributed to the significantly improved broad light absorption (400–3000 nm), more efficient charge separation and abundant active edge sites of monolayer MoS₂. The studies may provide a facile strategy for the fabrication of efficient plasmon‐enhanced photoelectrical NCs for HER.     

Constructing Pure Phase Tungsten‐Based Bimetallic Carbide Nanosheet as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Carbides are commonly regarded as efficient hydrogen evolution reaction (HER) catalysts, but their poor oxygen evolution reaction (OER) catalytic activities seriously limit their practical application in overall water splitting. Here, vertically aligned porous cobalt tungsten carbide nanosheet embedded in N‐doped carbon matrix (Co₆W₆C@NC) is successfully constructed on flexible carbon cloth (CC) as an efficient bifunctional electrocatalyst for overall water splitting via a facile metal–organic framework (MOF) derived method. The synergistic effect of Co and W atoms effectively tailors the electron state of carbide, optimizing the hydrogen‐binding energy. Thus Co₆W₆C@NC shows an enhanced HER performance with an overpotential of 59 mV at a current density of ?10 mA cm^?2. Besides, Co₆W₆C@NC easily in situ transforms into tungsten actived cobalt oxide/hydroxide during the OER process, serving as OER active species, which provides an excellent OER activity with an overpotential of 286 mV at a current density of ?10 mA cm^?2. The water splitting device, by applying Co₆W₆C@NC as both the cathode and anode, requires a low cell voltage of 1.585 V at 10 mA cm^?2 with the great stability in alkaline solution. This work provides a feasible strategy to fabricate bimetallic carbides and explores their possibility as bifunctional catalysts toward overall water splitting.     

Precursor‐Transformation Strategy Preparation of CuPx Nanodots–Decorated CoP3 Nanowires Hybrid Catalysts for Boosting pH‐Universal Electrocatalytic Hydrogen Evolution

The development of earth‐abundant, low cost, and versatile electrocatalysts for producing hydrogen from water electrolysis is still challenging. Herein, based on high hydrogen evolution reaction (HER) activity of transition metal phosphides, a CoP₃ nanowire decorated with copper phosphides (denoted as CuP_x) nanodots structures synthesized through a simple and easily scalable precursor‐transformation strategy is reported as a highly efficient HER catalyst. By decorating with CuP_x nanodots, the optimized CoP₃ nanowires electrode exhibits excellent catalytic activity and long‐term durability for HER in alkaline conditions, achieving a low overpotential of 49.5 mV at a geometrical catalytic current density of 10 mA cm^?2 with a small Tafel slope of 58.0 mV dec^?1, while also performing quite well in neutral and acidic media. Moreover, its overall performance exceeds most of the reported state‐of‐the‐art catalysts, especially under high current density of 100 mA cm^?2, demonstrating its potential as a promising versatile pH universal electrocatalyst for efficient water electrolysis. These results indicate that the incorporation of earth‐abundant stable element copper can significantly enhance catalytic activity, which widens the application range of copper and provides a new path for design and selection of HER catalysts.     

Colloidal Cobalt Phosphide Nanocrystals as Trifunctional Electrocatalysts for Overall Water Splitting Powered by a Zinc–Air Battery

Highly efficient and stable electrocatalysts, particularly those that are capable of multifunctionality in the same electrolyte, are in high demand for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). In this work, highly monodisperse CoP and Co₂P nanocrystals (NCs) are synthesized using a robust solution‐phase method. The highly exposed (211) crystal plane and abundant surface phosphide atoms make the CoP NCs efficient catalysts toward ORR and HER, while metal‐rich Co₂P NCs show higher OER performance owing to easier formation of plentiful Co₂P@COOH heterojunctions. Density functional theory calculation results indicate that the desorption of OH* from cobalt sites is the rate‐limiting step for both CoP and Co₂P in ORR and that the high content of phosphide can lower the reaction barrier. A water electrolyzer constructed with a CoP NC cathode and a Co₂P NC anode can achieve a current density of 10 mA cm^?2 at 1.56 V, comparable even to the noble metal‐based Pt/C and RuO₂/C pair. Furthermore, the CoP NCs are employed as an air cathode in a primary zinc–air battery, exhibiting a high power density of 62 mW cm^?2 and good stability.     

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.     

Boosting Water Dissociation Kinetics on Pt–Ni Nanowires by N‐Induced Orbital Tuning

Although it is commonly believed that the water‐dissociation‐related Volmer process is the rate‐limiting step for alkaline hydrogen evolution reaction (HER) on Pt‐based catalysts, the underlying essence, particularly on the atomic scale, still remains unclear. Herein, it is revealed that the sluggish water‐dissociation behavior probably stems from unfavorable orbital orientation and the kinetic issue is successfully resolved via N‐induced orbital tuning. Impressively, N modified Pt–Ni nanowires deliver an ultralow overpotential of 13 mV at 10 mA cm^?2, which represents a new benchmark for alkaline HER catalysis. Fine‐structural characterization and density functional theory analysis illustrate that the introduced nitrogen can uniquely modulate the electron densities around the Ni sites, and further create empty d_z² orbitals with superior orientation for water adsorption and activation. More importantly, it is demonstrated that N‐induced orbital modulation can generally boost the alkaline HER activities of Pt–Co, Pt–Ni, and Pt–Cu, offering a new perspective for the design of HER catalysts and beyond.     

Ruthenium Nanoparticles on Cobalt‐Doped 1T′ Phase MoS2 Nanosheets for Overall Water Splitting

2D MoS₂ nanostructures have recently attracted considerable attention because of their outstanding electrocatalytic properties. The synthesis of unique Co–Ru–MoS₂ hybrid nanosheets with excellent catalytic activity toward overall water splitting in alkaline solution is reported. 1T′ phase MoS₂ nanosheets are doped homogeneously with Co atoms and decorated with Ru nanoparticles. The catalytic performance of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is characterized by low overpotentials of 52 and 308 mV at 10 mA cm^?2 and Tafel slopes of 55 and 50 mV decade^?1 in 1.0 m KOH, respectively. Analysis of X‐ray photoelectron and absorption spectra of the catalysts show that the MoS₂ well retained its metallic 1T′ phase, which guarantees good electrical conductivity during the reaction. The Gibbs free energy calculation for the reaction pathway in alkaline electrolyte confirms that the Ru nanoparticles on the Co‐doped MoS₂ greatly enhance the HER activity. Water adsorption and dissociation take place favorably on the Ru, and the doped Co further catalyzes HER by making the reaction intermediates more favorable. The high OER performance is attributed to the catalytically active RuO₂ nanoparticles that are produced via oxidation of Ru nanoparticles.     

Ultrafine Co Nanoparticles Encapsulated in Carbon‐Nanotubes‐Grafted Graphene Sheets as Advanced Electrocatalysts for the Hydrogen Evolution Reaction

The rational design of an efficient and inexpensive electrocatalyst based on earth‐abundant 3d transition metals (TMs) for the hydrogen evolution reaction still remains a significant challenge in the renewable energy area. Herein, a novel and effective approach is developed for synthesizing ultrafine Co nanoparticles encapsulated in nitrogen‐doped carbon nanotubes (N‐CNTs) grafted onto both sides of reduced graphene oxide (rGO) (Co@N‐CNTs@rGO) by direct annealing of GO‐wrapped core–shell bimetallic zeolite imidazolate frameworks. Benefiting from the uniform distribution of Co nanoparticles, the in‐situ‐formed highly graphitic N‐CNTs@rGO, the large surface area, and the abundant porosity, the as‐fabricated Co@N‐CNTs@rGO composites exhibit excellent electrocatalytic hydrogen evolution reaction (HER) activity. As demonstrated in electrochemical measurements, the composites can achieve 10 mA cm^?2 at low overpotential with only 108 and 87 mV in 1 m KOH and 0.5 m H₂SO₄, respectively, much better than most of the reported Co‐based electrocatalysts over a wide pH range. More importantly, the synthetic strategy is versatile and can be extended to prepare other binary or even ternary TMs@N‐CNTs@rGO (e.g., Co–Fe@N‐CNTs@rGO and Co–Ni–Cu@N‐CNTs@rGO). The strategy developed here may open a new avenue toward the development of nonprecious high‐performance HER catalysts.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Superaerophobic Ultrathin Ni–Mo Alloy Nanosheet Array from In Situ Topotactic Reduction for Hydrogen Evolution Reaction

Hydrogen evolution reaction (HER) has prospect to becoming clean and renewable technology for hydrogen production and Ni–Mo alloy is among the best HER catalysts in alkaline electrolytes. Here, an in situ topotactic reduction method to synthesize ultrathin 2D Ni–Mo alloy nanosheets for electrocatalytic hydrogen evolution is reported. Due to its ultrathin structure and tailored composition, the as‐synthesized Ni–Mo alloy shows an overpotential of 35 mV to reach a current density of 10 mA cm^?2, along with a Tafel slope of 45 mV decade^?1, demonstrating a comparable intrinsic activity to state‐of‐art commercial Pt/C catalyst. Besides, the vertically aligned assemble structure of the 2D NiMo nanosheets on conductive substrate makes the electrode “superaerophobic,” thus leading to much faster bubble releasing during HER process and therefore shows faster mass transfer behavior at high current density as compared with drop drying Pt/C catalyst on the same substrate. Such in situ topotactic conversion finds a way to design and fabricate low‐cost, earth‐abundant non‐noble metal based ultrathin 2D nanostructures for electrocatalytic issues.     

Oxygen Doping to Optimize Atomic Hydrogen Binding Energy on NiCoP for Highly Efficient Hydrogen Evolution

An outstanding hydrogen evolution electrocatalyst should have a free energy of adsorbed atomic hydrogen of approximately zero, which enables not only a fast proton/electron‐transfer step but also rapid hydrogen release. An economic and industrially viable alternative approach for the optimization of atomic hydrogen binding energy is urgently needed. Herein, guided by density functional theory (DFT) calculations, it is theoretically demonstrated that oxygen doping in NiCoP can indeed optimize the atomic hydrogen binding energy (e.g., |ΔG_H*| = 0.08, 0.12 eV on Co, P sites). To confirm this, NiCoP electrodes with controllable oxygen doping are designed and fabricated via alteration of the reducing atmosphere. Accordingly, an optimal oxygen‐doped NiCoP (≈0.98% oxygen) nanowire array is found to exhibit the remarkably low hydrogen evolution reaction (HER) overpotential of 44 mV to drive 10 mA cm^?2 and a small Tafel slope of 38.6 mV dec^?1, and long‐term stability of 30 h in an alkaline medium. In neutral solution, only a 51 mV overpotential (@10 mA cm^?2) is required, and the Tafel slope is 79.2 mV dec^?1. Meanwhile, in situ Raman spectra confirm the low formation overpotential (?30 mV) of NiCo‐phosphate at the surface of ≈0.98% oxygen‐doped NiCoP, which enables the material to show better HER performance.     

Metal–Carbon Hybrid Electrocatalysts Derived from Ion‐Exchange Resin Containing Heavy Metals for Efficient Hydrogen Evolution Reaction

Transition metal–carbon hybrids have been proposed as efficient electrocatalysts for hydrogen evolution reaction (HER) in acidic media. Herein, effective HER electrocatalysts based on metal–carbon composites are prepared by controlled pyrolysis of resin containing a variety of heavy metals. For the first time, Cr₂O₃ nanoparticles of 3–6 nm in diameter homogeneously dispersed in the resulting porous carbon framework (Cr–C hybrid) is synthesized as efficient HER electrocatalyst. Electrochemical measurements show that Cr–C hybrids display a high HER activity with an onset potential of ?49 mV (vs reversible hydrogen electrode), a Tafel slope of 90 mV dec^?1, a large catalytic current density of 10 mA cm^?2 at ?123 mV, and the prominent electrochemical durability. X‐ray photoelectron spectroscopic measurements confirm that electron transfer occurs from Cr₂O₃ into carbon, which is consistent with the reported metal@carbon systems. The obtained correlation between metals and HER activities may be exploited as a rational guideline in the design and engineering of HER electrocatalysts.     

Non‐3d Metal Modulation of a 2D Ni–Co Heterostructure Array as Multifunctional Electrocatalyst for Portable Overall Water Splitting

Portable water splitting devices driven by rechargeable metal–air batteries or solar cells are promising, however, their scalable usages are still hindered by lack of suitable multifunctional electrocatalysts. Here, a highly efficient multifunctional electrocatalyst is demonstrated, i.e., 2D nanosheet array of Mo‐doped NiCo₂O₄/Co_5.47N heterostructure deposited on nickel foam (Mo‐NiCo₂O₄/Co_5.47N/NF). The successful doping of non‐3d high‐valence metal into a heterostructured nanosheet array, which is directly grown on a conductive substrate endows the resultant catalyst with balanced electronic structure, highly exposed active sites, and binder‐free electrode architecture. As a result, the Mo‐NiCo₂O₄/Co_5.47N/NF exhibits remarkable catalytic activity toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), affording high current densities of 50 mA cm^?2 at low overpotentials of 310 mV for OER, and 170 mV for HER, respectively. Moreover, a low voltage of 1.56 V is achieved for the Mo‐NiCo₂O₄/Co_5.47N/NF‐based water splitting cell to reach 10 mA cm^?2. More importantly, a portable overall water splitting device is demonstrated through the integration of a water‐splitting cell and two Zn–air batteries (open‐circuit voltage of 1.43 V), which are all fabricated based on Mo‐NiCo₂O₄/Co_5.47N/NF, demonstrating a low‐cost way to generate fuel energy. This work offers an effective strategy to develop high‐performance metal‐doped heterostructured electrode.     

Manipulation of Charge Transport by Metallic V13O16 Decorated on Bismuth Vanadate Photoelectrochemical Catalyst

Conductive metal oxides represent a new category of functional material with vital importance for many modern applications. The present work introduces a new conductive metal oxide V₁₃O₁₆, which is synthesized via a simplified photoelectrochemical procedure and decorated onto the semiconducting photocatalyst BiVO₄ in controlled mass percentages ranging from 25% to 37%. Owing to its excellent conductivity and good compatibility with oxide materials, the metallic V₁₃O₁₆‐decorated BiVO₄ hybrid catalyst shows a high photocurrent density of 2.2 ± 0.2 mA cm^?2 at 1.23 V versus reversible hydrogen electrode (RHE). Both experimental characterization and density functional theory calculations indicate that the superior photocurrent derives from enhanced charge separation and transfer, resulting from ohmic contact at the interface of mixed phases and superior electrical conductivity from V₁₃O₁₆. A Co–Pi coating on BiVO₄–V₁₃O₁₆ further increases the photocurrent to 5.0 ± 0.5 mA cm^?2 at 1.23 V versus RHE, which is among the highest reported for BiVO₄‐based photoelectrodes. Surface photovoltage and transient photocurrent measurements suggest a charge‐transfer model in which photocurrents are enhanced by improved surface passivation, although the barrier at the Co–Pi/electrolyte interface limits the charge transfer.