Co(OH)2 Nanoparticle-Encapsulating Conductive Nanowires Array: Room-Temperature Electrochemical Preparation for High-Performance Water Oxidation Electrocatalysis

The Single Atom Anchoring Strategy: Rational Design of MXene-Based Single-Atom Catalysts for Electrocatalysis

Single-atom catalysts (SACs) are a class of catalysts with low dosage, low cost, and the presence of metal atom-carrier interactions with high catalytic activity, which are considered to possess significant potential in the field of electrocatalysis. The most important aspect in the synthesis of SACs is the selection of suitable carriers. Metal carbides, nitrides, or carbon-nitrides (MXenes) are widely used as a new type of 2D materials with good electrical conductivity and tunable surface properties. The abundance of surface functional groups and vacancy defects on MXenes is an ideal anchoring site for metal single atoms and is therefore regarded as a good carrier for single-atom loading. In this work, the preparation method of MXenes, the loading mode of SACs, the characterization of the catalysts, and the electrochemical catalytic performance are described in detail, and some of the hot issues of the current research and future research directions are also summarized. The aim of this work is to promote the development of MXene-based SACs within the realm of electrocatalysis. With ongoing research and innovation, these materials are expected to be crucial in the future of energy conversion and storage solutions.

Modulating the Oxygen Evolution Reaction of Single-Crystal Cobalt Carbonate Hydroxide via Surface Fe Doping and Facet Dependence

The oxygen evolution reaction (OER) is a critical half-reaction in water splitting and metal-air cells. The sensitivity of the OER to the composition and structure of the electrocatalyst presents a significant challenge in elucidating the structure-property relationship. In this study, highly stable single-crystal cobalt carbonate hydroxide [Co2(OH)2CO3, CoCH] was used as a model to investigate the correlations among structure, composition, and reactivity. Single-crystal CoCH nanowires (denoted as CoCH NWs) and Fe-doped CoCH nanowires (denoted as Fe-CoCH NWs) with an exposed (210) facet and Fe-doped CoCH nanosheets (denoted as Fe-CoCH NSs) with an exposed (2-13) facet were synthesized using electrochemical and one-step hydrothermal strategies, respectively. Their OER activity decreased in the following order: Fe-CoCH NWs > Fe-CoCH NSs > CoCH NWs. Theoretical investigation suggested that the doped Fe sites serve as active sites, and the crystal-facet dependence can finely adjust the 3d configuration of Fe sites, resulting in the optimal adsorption strengths and energy barriers for potential-determining steps on the (210) facet of CoCH. This renders the as-prepared Fe-CoCH NWs as some of the most promising Co-based OER catalysts.

Promoted Two-Step Ammonia Synthesis with CoOOH/Co foam at Ampere-Level Current Density and Nearly 100% Faraday Efficiency from Air and Water

Ammonia (NH3) is regarded as an essential hydrogen storage material in the new energy field, and plasma-electrocatalytic synthesis of NH3 (PESA) is an alternative to the traditional Haber-Bosch process. Here, a bifunctional catalyst CoOOH/CF is proposed to enhance the PESA process. Benefiting from the efficient activation of O2 by CoOOH/CF, NOx - yield rate can reach the highest value of 171.90 mmol h-1 to date. Additionally, CoOOH holds a more negative d-band center, thereby exhibiting weaker adsorption toward NO*, lowering the energy barrier for the rate determining step, resulting in a high NH3 yield rate (302.55 mg h-1 cm-2 at -0.8 V) with ampere-level NH3 current density (2.86 A cm-2 at -0.8 V) and nearly 100% Faraday efficiency (FE, 99.8% at -0.6 V). Moreover, CoOOH/CF achieves an excellent 4.54 g h-1 NH3 yield rate with 97.9% FE in an enlarged electrolyzer, demonstrating the feasibility of PESA on a large scale.

Lattice Oxygen Activation through Deep Oxidation of Co4N by Jahn-Teller-Active Dopants for Improved Electrocatalytic Oxygen Evolution

Triggering the lattice oxygen oxidation mechanism is crucial for improving oxygen evolution reaction (OER) performance, because it could bypass the scaling relation limitation associated with the conventional adsorbate evolution mechanism through the direct formation of oxygen-oxygen bond. High-valence transition metal sites are favorable for activating the lattice oxygen, but the deep oxidation of pre-catalysts suffers from a high thermodynamic barrier. Here, taking advantage of the Jahn-Teller (J-T) distortion induced structural instability, we incorporate high-spin Mn3+ (t 2 g 3 e g 1 ${{t}_{2g}^{3}{e}_{g}^{1}}$ ) dopant into Co4N. Mn dopants enable a surface structural transformation from Co4N to CoOOH, and finally to CoO2, as observed by various in situ spectroscopic investigations. Furthermore, the reconstructed surface on Mn-doped Co4N triggers the lattice oxygen activation, as evidenced experimentally by pH-dependent OER, tetramethylammonium cation adsorption and online electrochemical mass spectrometry measurements of 18O-labelled catalysts. In general, this work not only offers the introducing J-T effect approach to regulate the structural transition, but also provides an understanding about the influence of the catalyst's electronic configuration on determining the reaction route, which may inspire the design of more efficient catalysts with activated lattice oxygen.

Interfacial charge transfer in sheet Ni2P-FePx heterojunction to promote the study of electrocatalytic oxygen evolution

The substantial expense associated with catalysts significantly hampers the progress of electrolytic water-based hydrogen production technology. There is an urgent need to find non-precious metal catalysts that are both cost-effective and highly efficient. Here, the porous Ni2P-FePx nanomaterials were successfully prepared by hydrothermal method, nickel foam as the base, iron nitrate solution as the caustic agent and iron source, and finally phosphating at low temperature. The obtained porous Ni2P-FePx nanosheets showed excellent catalytic activity under alkaline PH = 14, and an overpotential of merely 241 mV was required to achieve a current density of 50 mA cm-2. The morphology of the nanosheet can still be flawlessly presented on the screen after 50 h of working at high current density.

Amorphous Ni-Fe-Mo Oxides Coupled with Crystalline Metallic Domains for Enhanced Electrocatalytic Oxygen Evolution by Promoted Lattice-Oxygen Participation

The crystalline/amorphous heterophase nanostructures are promising functional materials for biomedicals, catalysis, energy conversion, and storage. Despite great progress is achieved, facile synthesis of crystalline metal/amorphous multinary metal oxides nanohybrids remains challenging, and their electrocatalytic oxygen evolution reaction (OER) performance along with the catalytic mechanism are not systematically investigated. Herein, two kinds of ultrafine crystalline metal domains coupled with amorphous Ni-Fe-Mo oxides heterophase nanohybrids, including Ni/Ni0.5-a Fe0.5 Mo1.5 Ox and Ni-FeNi3 /Ni0.5-b Fe0.5-y Mo1.5 Ox , are fabricated through controllable reduction of amorphous Ni0.5 Fe0.5 Mo1.5 Ox precursors by simply tuning the amount of used reductant. Due to the suited component in metal domains, the special structure with dense crystalline/amorphous interfaces, and strong electronic coupling of their components, the resultant Ni-FeNi3 /Ni0.5-b Fe0.5-y Mo1.5 Ox nanohybrids show greatly enhanced OER activity with a low overpotential (278 mV) to reach 10 mA cm-2 current density and ultrahigh turnover frequency (38160 h-1 ), outperforming Ni/Ni0.5-a Fe0.5 Mo1.5 Ox , Ni0.5 Fe0.5 Mo1.5 Ox precursors, commercial IrO2 , and most of recently reported OER catalysts. Also, such Ni-FeNi3 /Ni0.5-b Fe0.5-y Mo1.5 Ox nanohybrids manifest good catalytic stability. As revealed by a series of spectroscopy and electrochemical analyses, their OER mechanism follows the lattice-oxygen-mediated (LOM) pathway. This work may shed light on the design of advanced heterophase nanohybrids, and promote their applications in water splitting, metal-air batteries, or other clean energy fields.

Fe-induced crystalline-amorphous interface engineering of a NiMo-based heterostructure for enhanced water oxidation

Engineering heterostructures with a unique surface/interface structure is one of the effective strategies to develop highly active noble-metal-free catalysts for the oxygen evolution reaction (OER), because the surface/interface of catalysts is the main site for the OER. Herein, we design a coralloid NiMo(Fe)-20 catalyst with a crystalline-amorphous interface through combining a hydrothermal method and an Fe-induced surface reconfiguration strategy. That is, after Fe3+ impregnation treatment, the Ni(OH)2-NiMoO4 pre-catalyst with a complete crystalline surface is restructured into a trimetallic heterostructure with a crystalline-amorphous interface, which facilitates mass diffusion and charge transfer during the OER. As expected, self-supported NiMo(Fe)-20 exhibits excellent electrocatalytic water oxidation performance (overpotential: η-10 = 220 mV, η-100 = 239 mV) in the alkaline electrolyte, and its electrocatalytic performance hardly changes after maintaining the current density of 50 mA cm-2 for 10 hours. Furthermore, nickel foam (NF) supported commercial Pt/C and self-supported NiMo(Fe)-20 served as the cathode and anode of the Pt/C‖NiMo(Fe)-20 electrolyzer, respectively, which exhibits a lower cell voltage (E-100 = 1.53 V) than that of the Pt/C‖RuO2 electrolyzer (E-100 = 1.58 V) assembled with noble metal-based catalysts. The enhanced electrocatalytic performance of the NiMo(Fe)-20 catalyst is mainly attributed to the synergistic effect between the crystalline-amorphous interface and the coralloid trimetallic heterostructure.

Tweaking Photo CO2 Reduction by Altering Lewis Acidic Sites in Metalated-Porous Organic Polymer for Adjustable H2 /CO Ratio in Syngas Production

Herein, we have specifically designed two metalated porous organic polymers (Zn-POP and Co-POP) for syngas (CO+H2 ) production from gaseous CO2 . The variable H2 /CO ratio of syngas with the highest efficiency was produced in water medium (without an organic hole scavenger and photosensitizer) by utilizing the basic principle of Lewis acid/base chemistry. Also, we observed the formation of entirely different major products during photocatalytic CO2 reduction and water splitting with the help of the two catalysts, where CO (145.65 μmol g-1  h-1 ) and H2 (434.7 μmol g-1  h-1 ) production were preferentially obtained over Co-POP & Zn-POP, respectively. The higher electron density/better Lewis basic nature of Co-POP was investigated further using XPS, XANES, and NH3 -TPD studies, which considerably improve CO2 activation capacity. Moreover, the structure-activity relationship was confirmed via in situ DRIFTS and DFT studies, which demonstrated the formation of COOH* intermediate along with the thermodynamic feasibility of CO2 reduction over Co-POP while water splitting occurred preferentially over Zn-POP.

Nanoprecipitated CoPi enhanced photoelectrochemical water oxidation toward sensitive and selective Co2+ detection

The detection of heavy metal ions Co²⁺ is of great significance to the environment and human health. Herein, a simple, highly selective and sensitive photoelectrochemical detection strategy for Co²⁺ was developed based on the enhanced activity by nanoprecipitated CoPi on the Au nanoparticle decorated BiVO₄ electrode. The new photoelectrochemical sensor has a low detection limit of 0.03 μΜ and wide detection range of 0.1-10, and 10-6000 μΜ, with a high selectivity over other metal ions. The Co²⁺ concentration in tap water and commercial drinking water has also been successfully determined with the proposed method. Scanning electrochemical microscopy technique was employed to characterize the photocatalytic performance and heterogenous electron transfer rate of electrodes in situ, further revealing the photoelectrochemical sensing mechanism. Besides determining Co²⁺ concentration, this approach of enhanced catalytic activity by nanoprecipitation can be further extended to develop a variety of electrochemical, photoelectrochemical and optical sensing platforms for many other hazardous ions and biological molecules.

Interface Catalysts of Ni3Fe1 Layered Double Hydroxide and Titanium Carbide for High-Performance Water Oxidation in Alkaline and Natural Conditions

The electrocatalytic oxygen evolution reaction (OER) is important for many renewable energy technologies. Developing cost-effective electrocatalysts with high performance remains a great challenge. Here, we successfully demonstrate our novel interface catalyst comprised of Ni₃Fe₁-based layered double hydroxides (Ni₃Fe₁-LDH) vertically immobilized on a two-dimensional MXene (Ti₃C₂T_x) surface. The Ni₃Fe₁-LDH/Ti₃C₂T_x yielded an anodic OER current of 100 mA cm^-2 at 0.28 V versus reversible hydrogen electrode (RHE), nearly 74 times lower than that of the pristine Ni₃Fe₁-LDH. Furthermore, the Ni₃Fe₁-LDH/Ti₃C₂T_x catalyst requires an overpotential of only 0.31 V versus RHE to deliver an industrial-level current density as high as 1000 mA cm^-2. Such excellent OER activity was attributed to the synergistic interface effect between Ni₃Fe₁-LDH and Ti₃C₂T_x. Density functional theory (DFT) results further reveal that the Ti₃C₂T_x support can efficiently accelerate the electron extraction from Ni₃Fe₁-LDH and tailor the electronic structure of catalytic sites, resulting in enhanced OER performance.

Mild construction of an Fe-B-O based flexible electrode toward highly efficient alkaline simulated seawater splitting

It is essential to construct self-supporting electrodes based on earth-abundant iron borides in a mild and economical manner for grid-scale hydrogen production. Herein, a series of highly efficient, flexible, robust, and scalable Fe-B-O@FeB_x modified on hydrophilic cloth (denoted as Fe-B-O@FeB_x/HC, 10 cm × 10 cm) are fabricated by mild electroless plating. The overpotentials and Tafel slope values for the hydrogen and oxygen evolution reactions are 59 mV and 57.62 mV dec^-1 and 181 mV and 65.44 mV dec^-1, respectively; only 1.462 V is required to achieve 10 mA cm^-2 during overall water splitting (OWS). Fe-B-O@FeB_x/HC maintains its high catalytic activity for more than 7 days at an industrial current density (400 mA cm^-2), owing to the loosened popcorn-like Fe-B-O@FeB_x that is firmly loaded on a 2D-layered and mechanically robust substrate along with its fast charge and mass transfer kinetics. The chimney effect of core-shell borides@(oxyhydro)oxides enhances the OWS performance and protects the inner metal borides from further corrosion. Moreover, the flexible Fe-B-O@FeB_x/HC electrode has a low cost for grid-scale hydrogen production ($2.97 kg^-1). The proposed strategy lays a solid foundation for universal preparation, large-scale hydrogen production and practical applications thereof.

Fabrication of Ultra-Durable and Flexible NiPx -Based Electrode toward High-Efficient Alkaline Seawater Splitting at Industrial Grade Current Density

Designing nonprecious metal-based electrocatalysts to yield sustainable hydrogen energy by large-scale seawater electrolysis is challenging to global emissions of carbon neutrality and carbon peaking. Herein, a series of highly efficient, economical, and robust Ni-P-based nanoballs grown on the flexible and anti-corrosive hydrophobic asbestos (NiP_x @HA) is synthesized by electroless plating at 25 °C toward alkaline simulated seawater splitting. On the basis of the strong chemical attachment between 2D layered substrate and nickel-rich components, robust hexagonal Ni₅ P₄ crystalline modification, and fast electron transfer capability, the overpotentials during hydrogen/oxygen evolution reaction (HER/OER) are 208 and 392 mV at 200 mA cm^-2 , and the chronopotentiometric measurement at 500 mA cm^-2 lasts for over 40 days. Additionally, the versatile strategy is broadly profitable for industrial applications and enables multi-elemental doping (iron/cobalt/molybdenum/boron/tungsten), flexible substrate employment (nickel foam/filter paper/hydrophilic cloth), and scalable synthesis (22 cm × 22 cm). Density functional theory (DFT) also reveals that the optimized performance is due to the fundamental effect of incorporating O-source into Ni₅ P₄ . Therefore, this work exhibits a complementary strategy in the construction of NiP_x -based electrodes and offers bright opportunities to produce scalable hydrogen effectively and stably in alkaline corrosive electrolytes.

Heterostructured Co2P Nanocomposite Embedded in a N, P Co-Doped Carbon Layer as a High Performance Electrocatalyst for Overall Water Splitting

Hydrogen is the mainstream future energy source because of its high energy density and environmentally-friendly properties. In this study, Fe-Co2P/NPC materials were prepared by the wet chemical synthesis method, in which Fe-Co2P nanowires were wrapped by the N, P co-doped carbon layers (NPC) under aging and phosphorylation strategies. When Fe-Co2P/NPC/NF was subjected to hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), the overpotential was only 73 mV and 217 mV to reach the current density of 10 mA cm−2, respectively. When the cathode and anode were both Fe-Co2P/NPC/NF, a current density of 10 mA cm−2 was achieved with only 1.56 V. This work provides a new idea for the design and preparation of non-precious metal-based transition metal phosphide catalysts.

Co0.9Co0.1S Nanorods with an Internal Electric Field and Photothermal Effect Synergistically for Boosting Photocatalytic H2 Evolution

The paper reports a strategy to synthesize Cd_0.9Co_0.1S nanorods (NRs) via a one-pot solvothermal method. Remarkably, the pencil-shaped Cd_0.9Co_0.1S NRs with a large aspect ratio and good polycrystalline plane structure significantly shorten the photogenerated carrier transfer path and achieve fast separation. An appropriate amount of Co addition enhances visible light-harvesting and generates a photothermal effect to improve the surface reaction kinetics and increases the charge transfer rate. Moreover, the internal electric field facilitates the separation and transfer of carriers and effectively impedes their recombination. As a result, the optimized Cd_0.9Co_0.1S NRs yield a remarkable H₂ evolution rate of 8.009 mmol·g⁻¹·h⁻¹, which is approximately 7.2 times higher than that of pristine CdS. This work improves the photocatalytic hydrogen production rate by tuning and optimizing electronic structures through element addition and using the photothermal synergistic effect.

Defects engineering on CrOOH by Ni doping for boosting electrochemical oxygen evolution reaction

The design and construction of active centres are key to exploring advanced electrocatalysts for oxygen evolution reaction (OER). In this work, we demonstrate thein situconstruction of point defects on CrOOH by Ni doping (Ni-CrOOH/NF). Compared with pure CrOOH/NF, Ni-CrOOH/NF showed enhanced OER activity. The effect of the amount of Ni introduced on the OER performance was investigated. Ni_0.2-CrOOH/NF, the best introduction of Ni, uses a low overpotential of 253 mV to achieve a current density of 10 mA cm^-2with a high turnover frequency of 0.27 s^-1in 1.0 M NaOH. In addition, the electrocatalytic performance of Ni_0.2-CrOOH/NF showed little deterioration after 1000-cycle cyclic voltammetry scanning. In the potentiostatic test, activity was stable for at least 20 h.

Visible-light driven water oxidation and oxygen production at soft interfaces

The visible light driven water oxidation reaction (WOR) by the organic electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (TCNQF₄) was studied at the water|butyronitrile interface. The WOR was performed at neutral pH, and without any metal or organometallic catalysts. The oxygen generated was measured by GC-MS and cyclic voltammetry, and the protons produced were monitored by measuring the aqueous pH. This work opens novel perspectives for water photo-oxidation in liquids and artificial photosynthesis.

Ratiometric electrochemical immunoassay for procalcitonin based on dual signal probes: Ag NPs and Nile blue A

In order to determine procalcitonin, a sandwich-type ratiometic electrochemical immunosensor was developed by differential pulse voltammetry (DPV). Due to high chemical stability and good biocompatibility, graphitic carbon nitride (g-C₃N₄) could be used as feasible supporter to carry silver nanoparticles (Ag NPs) with an obvious oxidative peak (measured typically at + 0.3 V vs. SCE). Ag NPs loaded onto g-C₃N₄ were not only beneficial to prevent the agglomeration of Ag NPs, but also favorable to improve the electron transfer velocity of g-C₃N₄. Moreover, the g-C₃N₄-Ag NPs as the matrix could immobilize primary antibody by Ag-N bond. Nile blue A (NBA), an excellent redox probe based on the redox reaction with two-electrons, provides a current signal at - 0.38 V (vs. SCE). Zr-based metal organic framework (UiO-67), an ideal framework material with large specific surface area and high porosity, could absorb the substantial water-soluble NBA by electrostatic adsorption. The UiO-67 modified by NBA (NBA-UiO-67) owned admirable biocompatibility and was a qualifying marker to load the secondary antibody. For the immunosensor, the current ratio of NBA to Ag NPs (I_NBA/I_{Ag NPs}) was increased as the concentrations of PCT increased. Under the optimum conditions, the linear range of the immunosensor was 0.005 to 50 ng/mL; the detection limit was 1.67 pg/mL (S/N = 3), which reflected the excellent analytical performance of the sensor. The proposed immunosensor strategy is a simple and dependable platform, with great application potential in biometric analysis.

Carbon-quantum-dot-modified ZnS nanospheres for highly efficient electrocatalytic hydrogen evolution

CQDs modified ZnS nanospheres are modulated by tuning the addition of l-cysteine, and the CQDs attached on ZnS nanospheres plays an important role in improving the electron mobility and active areas, which determine the electrocatalytic performance.

Self-supported and defect-rich CoP nanowire arrays with abundant catalytic sites as a highly efficient bifunctional electrocatalyst for water splitting

In 1.0 M KOH, p-CoP/NF shows outstanding HER and OER activity. Furthermore when p-CoP/NF is assembled into a two-electrode cell, a voltage of only 1.55 V is needed to achieve 10 mA cm−2, and it can maintain long-term stability.

Sandwich-type photoelectrochemical immunosensor for procalcitonin detection based on Mn2+ doped CdS sensitized Bi2WO6 and signal amplification of NaYF4:Yb, Tm upconversion nanomaterial

In this paper, we constructed a sandwich-type photoelectrochemical (PEC) immunosensor for the quantitative detection of procalcitonin (PCT) based on the sensitization of Mn²⁺ doped CdS (CdS:Mn) nanocomposites to Bi₂WO₆ and the signal amplification effect of an upconversion material NaYF₄:Yb,Tm. Bi₂WO₆ was synthesized with a three-dimensional flowered structure. CdS:Mn reduced the recombination of photogenerated carriers, and significantly improved photocurrent response. Lanthanide-doped upconversion nanomaterials were used as the label of secondary antibody. NaYF₄:Yb,Tm have two functions, not only connected with the secondary antibody, but also can further amplify the photocurrent response. The proposed immunosensor for detecting PCT provided a desired linear range of 0.5 pg mL^-1-100 ng mL^-1 and a detection limit of 0.13 pg mL^-1 under optimal experimental conditions. Besides, the PEC immunosensor demonstrated good reproducibility, specificity and stability. The results of determination of PCT in real human serum samples were satisfactory. Thus, the immunosensor may be applied in the clinical diagnosis of PCT and other biomarkers.

Amorphous nickel tungstate films prepared by SILAR method for electrocatalytic oxygen evolution reaction

Development of electrocatalyst using facile way from non-noble metal compounds with high efficiency for effective water electrolysis is highly demanding for production of hydrogen energy. Nickel based electrocatalysts were currently developed for electrochemical water oxidation in alkaline pH. Herein, amorphous nickel tungstate (NiWO₄) was synthesized using the facile successive ionic layer adsorption and reaction method. The films were characterized by X-ray diffraction, Raman spectroscopy, Fourier transfer infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy techniques. The electrochemical analysis showed 315 mV of overpotential at 100 mA cm^-2 with lowest Tafel slope of 32 mV dec^-1 for oxygen evolution reaction (OER) making films of NiWO₄ compatible towards electrocatalysis of water in alkaline media. The chronopotentiometry measurements at 100 mA cm^-2 over 24 h showed 97% retention of OER activity. The electrochemical active surface area (ECSA) of NW120 film was 25.5 cm^-2.

Selenium-induced NiSe2@CuSe2 hierarchical heterostructure for efficient oxygen evolution reaction

Electrochemical water splitting is widely studied in the hope of solving environmental deterioration and energy shortage. The design of inexpensive metal catalysts exhibiting desired catalytic performance and durable stability for efficient oxygen evolution is the pursuit of sustainable and clean energy fields. Herein, a three-dimensional (3D) flower-like NiSe₂ primary structure, modified with highly dispersed CuSe₂ nanoclusters as the secondary structure, is obtained by regulating the growth trend of the nanosheets. Benefiting from the metallicity of selenides and the formation of a heterogeneous interface, NiSe₂@CuSe₂/NF shows comparable performance toward the oxygen evolution reaction (OER) in an alkaline environment. Upon regulating the synthesis conditions, the catalyst exhibits its optimal performance with ultralow overpotential for the OER when the Ni/Cu molar ratio is 1 : 0.2 and the hydrothermal temperature and hydrothermal time are 200 °C and 6 h, respectively. It provides a current density of 10 mA cm^-2 when a potential of 201 mV is applied without iR compensation. In this work, the hierarchical heterostructures of NiSe₂ and CuSe₂ are synthesized, which exhibit high electrocatalytic activity towards the oxygen evolution reaction and provides a new possibility for the extensive application of copper-based compounds in advanced energy fields.

"Pit-dot" ultrathin nanosheets of hydrated copper pyrophosphate as efficient pre-catalysts for robust water oxidation

Herein, hydrated copper pyrophosphate ultrathin nanosheets with a unique "pit-dot" nanostructure were fabricated as efficient pre-catalysts for the oxygen evolution reaction, and systematic post-catalytic characterization studies confirmed the important role of the boosted pre-oxidation reaction in promoting the OER catalysis.

Structural and Interfacial Engineering of Ni2P/Fe3O4 Porous Nanosheet Arrays for Efficient Oxygen Evolution Reaction

Rational design of transition-metal phosphide (TMPs)-based electrocatalysts can effectively promote oxygen evolution reaction (OER). Herein, the novel efficient Ni₂P/Fe₃O₄ porous nanosheets arrays supported on Ni foam (Ni₂P/Fe₃O₄/NF) as alkaline OER catalysts were synthesized using structural and interfacial engineering. The three-dimensional (3D) porous hierarchical structure of Ni₂P/Fe₃O₄/NF provides abundant active sites for OER and facilitates the electrolyte diffusion of ions and O₂ liberation. Furthermore, the strong interfacial coupling and synergistic effect between Ni₂P and Fe₃O₄ modify the electronic structure, resulting in the enhanced intrinsic activity. Consequently, the optimized Ni₂P/Fe₃O₄/NF exhibits excellent OER performance with low overpotentials of 213 and 240 mV at 60 and 100 mA cm^-2 in 1.0 M KOH, respectively, better than the RuO₂/NF and most Ni/Fe-based OER catalysts. Impressively, it can maintain its catalytic activity for at least 20 h at 60 mA cm^-2. In addition, the relationship between the structure and performance is fully elucidated by the experimental characterizations, indicating that the metal oxyhydroxides in situ generated on the surface of catalysts are responsible for the high OER activity.

Discharge-Induced Enhancement of the Oxygen Evolution Reaction

The fundamental understanding of the surface reconstruction induced by the applied potential is of great significance for enhancing the oxygen evolution reaction (OER). Here, we show that a previously overlooked discharge current in the low applied potential region also leads to in situ electrochemical activation of a nitrogen-doped nickel oxyhydroxide surface. We exploit the fact that doping of heteroatoms weakens the surface structure, and hence, a weak discharge current originating from the capacitive nature of nickel oxyhydroxide has a strong structure-reforming ability to promote the formation of nitrogen and oxygen vacancies. The current density at 1.4 V (vs. Hg/HgO) can dramatically increase by as much as 31.3 % after discharge in the low applied potential region. This work provides insight into in situ enhancement of the OER and suggests that the low applied potential region must be a primary consideration in evaluating the origin of the activity of electrocatalysts.

Sodium-Decorated Amorphous/Crystalline RuO2 with Rich Oxygen Vacancies: A Robust pH-Universal Oxygen Evolution Electrocatalyst

The oxygen evolution reaction (OER) is a key reaction for many electrochemical devices. To date, many OER electrocatalysts function well in alkaline media, but exhibit poor performances in neutral and acidic media, especially the acidic stability. Herein, sodium-decorated amorphous/crystalline RuO₂ with rich oxygen vacancies (a/c-RuO₂ ) was developed as a pH-universal OER electrocatalyst. The a/c-RuO₂ shows remarkable resistance to acid corrosion and oxidation during OER, which leads to an extremely high catalytic stability, as confirmed by a negligible overpotential increase after continuously catalyzing OER for 60 h at pH=1. Besides, a/c-RuO₂ also exhibits superior OER activities to commercial RuO₂ and most reported OER catalysts under all pH conditions. Theoretical calculations indicated that the introduction of Na dopant and oxygen vacancy in RuO₂ weakens the adsorption strength of the OER intermediates by engineering the d-band center, thereby lowering the energy barrier for OER.

Conductive Polymer Intercalation Tunes Charge Transfer and Sorption-Desorption Properties of LDH Enabling Efficient Alkaline Water Oxidation

Controlling and tuning surface properties of a catalyst have always been a prime challenge for efficient hydrogen production via water splitting. Here, we report a facile method for tuning both charger transfer and sorption-desorption properties of NiFe layered double hydroxide (LDH) by intercalating a conductive polymer of polypyrrole (ppy) via an interlayer confined polymerization synthesis (ICPS) process. Ex situ characterizations and in situ electrochemical quartz-crystal microbalance with dissipation (EQCM-D) tracking experiments showed that the intercalated ppy not only improved the charge transfer property of the resulting hybrid catalyst LDH-ppy but also made it more flexible and adaptive for quick and reversible sorption-desorption of reactants and intermediates during the oxygen evolution reaction (OER) process. Consequently, the as-prepared LDH-ppy exhibited a doubled catalytic current density over the bare LDH, as visualized by in situ scanning electrochemical microscopy (SECM) at the subnanometer scale. This work sheds light on orchestrating the charge and sorbate transfer abilities of catalysts for efficient water splitting by smartly combining inorganic and organic layers.

NiFe Layered-Double-Hydroxide Nanosheet Arrays on Graphite Felt: A 3D Electrocatalyst for Highly Efficient Water Oxidation in Alkaline Media

It is of great importance to rationally design and develop earth-abundant nanocatalysts for high-efficiency water electrolysis. Herein, NiFe layered double hydroxide was in situ grown hydrothermally on a 3D graphite felt (NiFe LDH/GF) as a high-efficiency catalyst in facilitating the oxygen evolution reaction (OER). In 1.0 M KOH, NiFe LDH/GF requires a low overpotential of 214 mV to deliver a geometric current density of 50 mA cm^-2 (η_{50 mA cm^-2} = 214 mV), surpassing that NiFe LDH supported on a 2D graphite paper (NiFe LDH/GP; η_{50 mA cm^-2} = 301 mV). More importantly, NiFe LDH/GF shows good durability at 50 mA cm^-2 within 50 h of OER catalysis testing and delivers a faradaic efficiency of nearly 100% in the electrocatalysis of OER.

Fe, Ni-codoped W18O49 grown on nickel foam as a bifunctional electrocatalyst for boosted water splitting

Designing cost-effective bifunctional catalysts with high-performance and durability is of great significance for renewable energy systems. Herein, typical Fe, Ni-codoped W₁₈O₄₉/NF was prepared via a simple solvothermal method. The incorporation of Fe ions enhanced the electronic interaction and enlarged the electrochemically active surface area. The increased W⁴⁺ leads to a high proportion of unsaturated W[double bond, length as m-dash]O bonds, thus enhancing the adsorption capacity of water. The valence configuration of nickel (Ni) sites in such dual-cation doping is well adjusted, realizing a high proportion of trivalent Ni ions (Ni³⁺). Due to the orbital interactions, the Fe³⁺/Ni³⁺ ions and OER reaction intermediates exhibit strong orbital overlap. The positions of the valence band and conduction band are well modulated. As a result, the Fe, Ni-codoped W₁₈O₄₉/NF shows improved electrocatalytic activity, and achieves a low decomposition voltage of 1.58 V at 10 mA cm^-2 and retains long-time stability.

An ingeniously assembled metal-organic framework on the surface of FeMn co-doped Ni(OH)2 as a high-efficiency electrocatalyst for the oxygen evolution reaction

To overcome the problem of the sluggish kinetics of the oxygen evolution reaction (OER), it is of great significance to develop an efficient and stable non-noble metal-based OER catalyst for electrocatalytic energy conversion and storage. Herein, a complex of a metal-organic framework and hydroxide is synthesized by performing a ligand etching strategy on FeMn co-doped Ni(OH)₂ nanosheets in situ grown on nickel foam (FeMn-Ni(OH)₂@MOF/NF). Benefiting from the unique sheet-on-sheet hierarchical structure, multi-metal active nodes and two active materials grown in situ, the resulting FeMn-Ni(OH)₂@MOF/NF demonstrated brilliant OER activity with an overpotential of 199 mV to achieve a current density of 10 mA cm^-2 and long-term stability. This research will provide a new strategy for the design of high-performance OER electrocatalysts.

Constructing RuCoOx /NC Nanosheets with Low Crystallinity within ZIF-9 as Bifunctional Catalysts for Highly Efficient Overall Water Splitting

Electrocatalysts play a pivotal role in accelerating the sluggish electrochemical water splitting reaction. Herein, a Ru-Co oxides and carbon nitrides hybrid (RuCoO_x /NC) electrocatalyst was constructed by employing ZIF-9 to disperse Ru precursor and deliberately regulating the calcination temperature. The moderate calcination temperature results in the RuCoO_x nanocomposites with small particle size and low crystallinity as well as the co-existence of multi-valence metal compounds, thus boosting the amount and species of active sites. Moreover, the strong interactions between Co and Ru species induce the electron transfer from Co to Ru, thus enhancing the adsorption of anion intermediates on the electron-deficient Co species and the proton capturing capacity of electron-sufficient Ru species. As a result, the optimized RuCoO_x /NC-350 catalyst behaved good electrocatalytic activities with 73 and 210 mV overpotential to achieve 10 mA cm^-2 for HER and OER, respectively. Remarkably, it showed good durability by holding at 100 mA cm^-2 for 100 h in HER and 50 mA cm^-2 for 24 h in OER with small activity decline. This study may shed new light on the rational construction of highly efficient Ru-based catalysts for electrochemical water splitting.

NiCo2O4 nanoparticles inlaid on sulphur and nitrogen doped and co-doped rGO sheets as efficient electrocatalysts for the oxygen evolution and methanol oxidation reactions

The present work depicts the fabrication of NiCo₂O₄ decorated on rGO, and doped and co-doped rGO and its electrocatalytic activity towards the oxygen evolution reaction and methanol oxidation reaction. The NiCo₂O₄ catalyst with S-doped rGO outperformed the other catalysts, indicating that the sulphur atoms attached on rGO possess low oxophilicity and optimum free energy. This results in facile adsorption of the intermediate products formed during the OER and a rapid release of O₂ molecules. The same catalyst requires an overpotential of 1.51 V vs. RHE to attain the benchmark current density value of 10 mA cm^-2 and shows a Tafel slope of 57 mV dec^-1. It also reveals outstanding stability during its operation for 10 h with a minimum loss in potential. On the other hand, NiCo₂O₄/S,N-rGO reveals superior activity with high efficiency and stability in catalyzing methanol oxidation. The catalyst delivered a low onset potential of 0.12 V vs. Hg/HgO and high current density of 203.4 mA cm^-2 after addition of 0.5 M methanol, revealing the outstanding performance of the electrocatalyst.

In situsynthesis of Fe-doped CrOOH nanosheets for efficient electrocatalytic water oxidation

The oxygen evolution reaction (OER) is a process in electrochemical water splitting with sluggish kinetics that needs efficient non-noble-metal electrocatalysts. There have been few studies of CrOOH electrocatalysts for water oxidation due to their low performance. Herein,in situsynthesized Fe-doped CrOOH nanosheets on Ni foam (Fe-CrOOH/NF) were designed as electrocatalysts and performance in the OER was obviously improved. The effect of the amount of Fe doping was also investigated. Experiments revealed that the best performance of Fe-CrOOH/NF requires low overpotentials of 259 mV to reach 20 mA cm^-2together with a turnover frequency of 0.245 s^-1in 1.0 M KOH, which may suggest a new direction for the development of Fe-doped OER electrocatalysts.

Co9S8 Nanosheet Coupled Cu2S Nanorod Heterostructure as Efficient Catalyst for Overall Water Splitting

Electrocatalytic water splitting is a promising technology for large-scale hydrogen production. However, it requires efficient catalysts to overcome the large overpotentials in the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, we report a novel heterostructure catalyst Co₉S₈/Cu₂S on copper foam (Co₉S₈/Cu₂S/CF) with multistep impregnation and electrodeposition. Due to the strong interfacial interaction, the interfacial electrons transfer from Co sites to S sites, which promote the adsorption of oxygen-containing intermediates, water molecules, as well as the dissociation of water molecules. Therefore, the heterostructure catalyst exhibits low overpotentials of 195 mV for OER and 165 mV for HER at 10 mA cm^-2, respectively. Moreover, it only needs 1.6 V to realize water splitting at 10 mA cm^-2 in a two-electrode cell. This work provides an efficient method to tailor the surface electronic structure through specific morphological design and construct a heterostructure interface to achieve alkaline water splitting.

Exploiting Ru-Induced Lattice Strain in CoRu Nanoalloys for Robust Bifunctional Hydrogen Production

Designing bifunctional catalysts capable of driving the electrochemical hydrogen evolution reaction (HER) and also H2 evolution via the hydrolysis of hydrogen storage materials such as ammonia borane (AB) is of considerable practical importance for future hydrogen economies. Herein, we systematically examined the effect of tensile lattice strain in CoRu nanoalloys supported on carbon quantum dots (CoRu/CQDs) on hydrogen generation by HER and AB hydrolysis. By varying the Ru content, the lattice parameters and Ru-induced lattice strain in the CoRu nanoalloys could be tuned. The CoRu0.5 /CQDs catalyst with an ultra-low Ru content (1.33 wt.%) exhibited excellent catalytic activity for HER (η=18 mV at 10 mA cm-2 in 1 M KOH) and extraordinary activity for the hydrolysis of AB with a turnover frequency of 3255.4 mol( H 2 )  mol-1 (Ru)  min-1 or 814.7 mol( H 2 )  mol-1 (cat)  min-1 at 298 K, respectively, representing one of the best activities yet reported for AB hydrolysis over a ruthenium alloy catalyst. Moreover, the CoRu0.5 /CQDs catalyst displayed excellent stability during each reaction, including seven alternating cycles of HER and AB hydrolysis. Theoretical calculations revealed that the remarkable catalytic performance of CoRu0.5 /CQDs resulted from the optimal alloy electronic structure realized by incorporating small amounts of Ru, which enabled fast interfacial electron transfer to intermediates, thus benefitting H2 evolution kinetics. Results support the development of new and improved catalysts HER and AB hydrolysis.

High-entropy alloys for water oxidation: a new class of electrocatalysts to look out for

High-entropy alloys (HEAs) with five or more elements can provide near-continuous adsorption energies and can be optimized for superior persistent catalytic activity. This report presents electrochemical water oxidation facilitated by employing graphene and FeCoNiCuCr HEA nanoparticle based composites prepared via the mechanical milling of graphite-metal powders. The composite efficiently facilitates water oxidation with a low overpotential of 330 mV at 10 mA cm-2, and high specific and mass activities (∼143 mA cm-2 and 380 mA mg-1, respectively, at 1.75 V). Importantly, the composites exhibit excellent accelerated cycling stability with ∼99% current retention (after 3250 cycles). The HEA-based composites are anticipated to replace noble/precious metal based traditional electrocatalysts in the future, the use of which is a major obstacle in the technological scalability of electrochemical energy conversion and storage devices.