In Situ Growth of Ag Nanodots Decorated Cu2 O Porous Nanobelts Networks on Copper Foam for Efficient HER Electrocatalysis

Highly Selective CO2 Electroreduction to C2H4 Using a Dual-Sites Cu(II) Porphyrin Framework Coupled with Cu2O Nanoparticles via a Synergetic-Tandem Strategy

Low *CO coverage on the active sites is a major hurdle in the tandem electrocatalysis, resulting in unsatisfied C2H4 production efficiencies. In this work, we developed a synergetic-tandem strategy to construct a copper-based composite catalyst for the electroreduction of CO2 to C2H4, which was constructed via the template-directed polymerization of ultrathin Cu(II) porphyrin organic framework incorporating atomically isolated Cu(II) porphyrin and Cu(II) bipyridine sites on a carbon nanotube (CNT) scaffold, and then Cu2O nanoparticles were uniformly dispersed on the CNT scaffold. The presence of dual active sites within the Cu(II) porphyrin organic framework create a synergetic effect, leading to an increase in local *CO availability to enhance the C-C coupling step implemented on the adjacent Cu2O nanoparticles for further C2H4 production. Accordingly, the resultant catalyst affords an exceptional CO2-to-C2H4 Faradaic efficiency (FEC2H4) of 71.0 % at -1.1 V vs reversible hydrogen electrode (RHE), making it one of the most effective copper-based tandem catalysts reported to date. The superior performance of the catalyst is further confirmed through operando infrared spectroscopy and theoretic calculations.

Ag engineered NiFe-LDH/NiFe2O4 Mott-Schottky heterojunction electrocatalyst for highly efficient oxygen evolution and urea oxidation reactions

Efficient and durable electrocatalysts with sufficient active sites and high intrinsic activity are essential for advancing energy-saving hydrogen production technology. In this study, a Mott-Schottky heterojunction electrocatalyst with Ag nanoparticles in-situ grown on NiFe layered double hydroxides (NiFe-LDH)/NiFe2O4 nanosheets (Ag@NiFe-LDH/NiFe2O4) were designed and successfully synthesized through a hydrothermal process and subsequent spontaneous redox reaction. The in-situ growth of metallic Ag on semiconducting NiFe-LDH/NiFe2O4 triggers a strong electron interaction across the Mott-Schottky interface, leading to a significant increase in both the intrinsic catalytic activity and the electrochemical active surface area of the heterojunction electrocatalyst. As a result, the Ag@NiFe-LDH/NiFe2O4 demonstrates impressive oxygen evolution reaction (OER) performance in alkaline KOH solution, achieving a low overpotential of 249 mV at 100 mA cm-2 and a Tafel slope of 42.79 mV dec-1. When the self-supported Ag@NiFe-LDH/NiFe2O4 is coupled with the Pt/C electrocatalyst, the alkaline electrolyzer reaches a current density of 10 mA cm-2 at a cell voltage of only 1.460 V. Furthermore, X-ray photoelectron spectroscopy and in-situ Raman analysis reveal that the Ni(Fe)OOH is the possible active phase for OER in the catalyst. In addition, when employed for UOR catalysis, the Ag@NiFe-LDH/NiFe2O4 also displays intriguing activity with an ultralow potential of 1.389 V at 50 mA cm-2. This work may shed light on the rational design of multiple-phase heterogeneous electrocatalysts and demonstrate the significance of interface engineering in enhancing catalytic performance.

Transition Metals-Based Water Splitting Electrocatalysts on Copper-Based Substrates: The Integral Role of Morphological Properties

Electrocatalytic water splitting is a promising alternative to produce high purity hydrogen gas as the green substitute for renewable energy. Thus, development of electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are vital to improve the efficiency of the water splitting process particularly based on transition metals which has been explored extensively to replace the highly active electrocatalytic activity of the iridium and ruthenium metals-based electrocatalysts. In situ growth of the material on a conductive substrate has also been proven to have the capability to lower down the overpotential value significantly. On top of that, the presence of substrate has given a massive impact on the morphology of the electrocatalyst. Among the conductive substrates that have been widely explored in the field of electrochemistry are the copper based substrates mainly copper foam, copper foil and copper mesh. Copper-based substrates possess unique properties such as low in cost, high tensile strength, excellent conductor of heat and electricity, ultraporous with well-integrated hierarchical structure and non-corrosive in nature. In this review, the recent advancements of HER and OER electrocatalysts grown on copper-based substrates has been critically discussed, focusing on their morphology, design, and preparation methods of the nanoarrays.

Electronic Modulation and Mechanistic Study of Ru-Decorated Porous Cu-Rich Cuprous Oxide for Robust Alkaline Hydrogen Oxidation and Evolution Reactions

Rational design of high-efficiency and viable electrocatalysts is essential in overcoming the bottleneck of sluggish alkaline hydrogen oxidation/evolution reaction (HOR/HER) kinetics. In this study, a metal-organic framework-derived strategy for constructing a Pt-free catalyst with Ru clusters anchored on porous Cu-Cu₂ O@C is proposed. The designed Ru/Cu-Cu₂ O@C exhibits superior HOR performance, with a mass activity of 2.7 mA  μ g R u - 1 ${{{\rm \mu }{\rm g}}_{{\rm R}{\rm u}}^{-1}}$ at 50 mV, which is about 24 times higher than that of state-of-the-art Pt/C (0.11 mA  μ g P t - 1 ${{{\rm \mu }{\rm g}}_{{\rm P}{\rm t}}^{-1}}$ ). Significantly, Ru/Cu-Cu₂ O@C also displays impressive HER performance by generating 26 mV at 10 mA cm^-2 , which exceeds the majority of documented Ru-based electrocatalysts. Systematic characterization and density functional theory (DFT) calculations reveal that efficient electron transfer between Ru and Cu species results in an attenuated hydrogen binding energy (HBE) of Ru and an enhanced hydroxy binding energy (OHBE) of Cu₂ O, together with an optimized H₂ O adsorption energy with Cu₂ O as the H₂ O*-capturing site, which jointly facilitates HOR and HER kinetics.

In-situ construction of Au/Cu2O nanowire arrays for sensitive glucose sensing

Architecture design is widely regarded as a rational strategy to enhance the sensing performance of electrocatalysts. Herein, the novel three-dimensional hybrids based on Au and Cu₂O were successfully synthesized via steps of in-situ growth, including anodic oxidation, annealing and galvanic displacement. Cu₂O appeared in the morphology of nanowire array on conductive substrate, and was decorated by Au nanoparticles. Benefiting from the unique architecture and binder-free fabrication process, the Au/Cu₂O nanowire arrays possessed high conductivity and abundant exposed active sites, as well as facilitated the direct electron transfer among detection object, electrocatalyst and current collector. Moreover, Au/Cu₂O particles as contrast were fabricated to clarify the effect of structure on sensing ability. The Au/Cu₂O nanowire arrays drove the glucose electro-oxidation reaction with great catalytic activity, in which a potential as low as 0.4 V was needed to reach a high sensitivity of 2.098 mA mM^-1 cm^-2. The excellent selectivity, stability and reproducibility were also obtained by the sensor. Furthermore, the quantitative detection of glucose level in diluted human serum were performed and the satisfactory result make the obtained sensor have the potential for practical applications.

Super-Hydrophilic Microporous Ni(OH)x/Ni3 S2 Heterostructure Electrocatalyst for Large-Current-Density Hydrogen Evolution

Exploiting active and stable non-precious metal electrocatalysts for alkaline hydrogen evolution reaction (HER) at large current density plays a key role in realizing large-scale industrial hydrogen generation. Herein, a self-supported microporous Ni(OH)x/Ni₃ S₂ heterostructure electrocatalyst on nickel foam (Ni(OH)x/Ni₃ S₂ /NF) that possesses super-hydrophilic property through an electrochemical process is rationally designed and fabricated. Benefiting from the super-hydrophilic property, microporous feature, and self-supported structure, the electrocatalyst exhibits an exceptional HER performance at large current density in 1.0 M KOH, only requiring low overpotential of 126, 193, and 238 mV to reach a current density of 100, 500, and 1000 mA cm^-2 , respectively, and displaying a long-term durability up to 1000 h, which is among the state-of-the-art non-precious metal electrocatalysts. Combining hard X-rays absorption spectroscopy and first-principles calculation, it also reveals that the strong electronic coupling at the interface of the heterostructure facilitates the dissociation of H₂ O molecular, accelerating the HER kinetics in alkaline electrolyte. This work sheds a light on developing advanced non-precious metal electrocatalysts for industrial hydrogen production by means of constructing a super-hydrophilic microporous heterostructure.

Plasmonic Ag-decorated Cu2O nanowires for boosting photoelectrochemical CO2 reduction to multi-carbon products

The generation of multi-carbon products on the Cu₂O photocathode remains a great challenge. Herein, effective charge separation and surface catalytic reaction are achieved for photoelectrochemical CO₂ reduction through plasmon metal (Ag) decoration on Cu₂O nanowires. The Cu₂O/Ag composite photocathode achieves a 47.7% faradaic efficiency for CH₃COOH and the generation rate is 212.7 μmol cm^-2 h^-1 under illumination, which is about five times that in dark (44.4 μmol cm^-2 h^-1) at -0.7 V vs. RHE.

Optimizing electronic structure of porous Ni/MoO2 heterostructure to boost alkaline hydrogen evolution reaction

Heterostructure engineering is an efficient strategy to synergisticallyimprove electrocatalytic activity. In this work, Ni/MoO₂ heterojunction nanorods with porous structure self-supported on nickel foam (NF) are elaborately designed through a facile solution-evaporationmethod followed by a thermal reduction process. Prominently, the optimal electrocatalyst Ni/MoO₂@NF-E delivers an exceptionally low overpotential of 19 mV at the current density of 10 mA cm^-2 and a small Tafel slope of 52.3 mV dec^-1 toward the hydrogen evolution reaction (HER) in alkaline solution. Concurrently, Ni/MoO₂@NF-E also maintains excellent stability after 120 h of electrolysis or 5000 cyclic voltammetry cycles. The experimental and density functional theory (DFT) results indicate that the enhanced HER performance of Ni/MoO₂@NF-E should be ascribed to the porous structure in the Ni/MoO₂ nanorods providing more active catalytic site, the moderate Gibbs free energy of hydrogen adsorption (ΔG_H*), as well as strong synergistic effect between Ni and MoO₂. This work provides an efficient route for developing HER electrocatalysts in alkaline media.

Enhanced catalytic reduction of p-nitrophenol and azo dyes on copper hexacyanoferrate nanospheres decorated copper foams

Catalytic reduction of nitroaromatic compounds using low-cost non-precious metal containing catalyst remains an essential topic in wastewater treatment. Herein, copper hexacyanoferrate nanospheres decorated copper foams (CF) were prepared by a facile method, and it was used as structured catalysts for the reduction of p-nitrophenol (p-NP) and azo dyes. The catalyst obtained by calcination at 200 °C shows the highest catalytic activity, with an almost complete reduction of p-NP within 3 min with a rate of 2.057 min^-1 at room temperature, and it exhibited excellent reusability in successive 6 cycles. The effects of temperature, initial concentration, pH, and flow rate on p-NP reduction were investigated. Moreover, the mechanistic investigation revealed that fast electron transfer ability and enhanced adsorption for p-NP contributed to its enhanced catalytic performances. This work put forward an efficient approach for the construction of structured catalysts with enhanced performance in catalytic reduction applications.

Cu-NPs@C Nanosheets Derived from a PVP-assisted 2D Cu-MOF with Renewable Ligand for High-Efficient Selective Hydrogenation of 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF) containing C=O, C-O, and furan ring functional groups is an important platform chemical derived from C₆ sugars. The selective hydrogenation of C=O in HMF produces 2,5-dihydroxymethylfuran (DHMF), which is a potential sustainable substitute for petroleum-based building blocks. Here, 2,5-furandicarboxylic acid (H₂ FDC), a promising sustainable alternative to terephthalic acid, was employed as a renewable ligand to synthesize a novel Cu metal-organic framework (Cu-FDC). With a polyvinyl pyrrolidone (PVP)-assisted approach, 2D Cu-FDC nano-lamellae of micrometer lateral dimensions and nanometer thickness could be obtained, which could be used as a precursor to fabricate 2D oxygen-rich carbon nanosheets embedded with Cu nanoparticles (denoted CFP-300) after a thermal treatment at 300 °C under N₂ atmosphere. The synthesized CFP-300 exhibited excellent catalytic performance and stability for the selective hydrogenation of HMF to DHMF. These results demonstrated a sustainable route to synthesize efficient catalysts by employing metal-organic frameworks based on renewable ligands.

High-performance self-supporting AgCoPO4/CFP for hydrogen evolution reaction under alkaline conditions

Electrochemical water decomposition to produce hydrogen is a promising approach for renewable energy storage. It is vital to develop a catalyst with low overpotential, low cost and high stability for hydrogen evolution reaction (HER) under alkaline conditions. Herein, we used a simple hydrothermal method to obtain a AgCo(CO)₄ precursor on the surface of carbon fiber paper (CFP). After thermal phosphorization, the self-supporting catalyst AgCoPO₄/CFP was obtained, which greatly improved the HER catalytic performance under alkaline conditions. At 10 mA cm^-2, it showed an overpotential of 32 mV. The Tafel slope was 34.4 mV dec^-1. The high catalytic performance of AgCoPO₄/CFP may be due to the hydrophilic surface promoting effective contact with the electrolyte and the synergistic effect of the two metals, which accelerated electron transfer and thus promoted hydrogen evolution reaction. In addition, it showed an outstanding urea oxidation reaction (UOR) activity. After adding 0.5 M urea, the over-potential of the AgCoPO₄/CFP assembled electrolytic cell was only 1.45 V when the current density reached 10 mA cm^-2, which was much lower than that required for overall water splitting. This work provides a new method for the design and synthesis of efficient HER electrocatalysts.

Heterostructure of Semiconductors on Self-Supported Cuprous Phosphide Nanowires for Enhanced Overall Water Splitting

Rational design, controllable synthesis, and an in-depth mechanism study of Cu-based bifunctional semiconductor heterostructures toward overall water splitting (OWS) are imperative but still face challenges. Herein, n-type iron oxide and p-type nickel phosphide and cobalt phosphide are respectively coupled with p-type cuprous phosphide nanowires on Cu foams via a general growth-phosphorization strategy. These self-supported semiconductor heterojunctions with different built-in potentials (E_BI) are used as binder-free electrodes for OWS and exhibit significantly improved electrocatalytic activities compared to their counterparts. Among them, the heterostructure with the largest E_BI of 1.57 V attains the smallest overpotential of 97 mV at 10 mA cm^-2 for the hydrogen evolution reaction and 243 mV at 50 mA cm^-2 for the oxygen evolution reaction in 1 M KOH. The corresponding two-electrode electrolyzer requires a cell voltage of 1.685 V at 50 mA cm^-2 and shows admirable long-term stability at 100 mA cm^-2 with a Faraday efficiency of around 98%. These promoted electrocatalytic performances originate from the enhanced active site, accelerated charge transfer, enlarged electrochemical active surface area, and synergy between different components at the heterointerface. This work represents a promising avenue to construct cost-efficient semiconductor heterostructures as bifunctional electrocatalysts applied to the sustainable energy industry.

Metal‐Organic Framework Derived Carbon-Encapsulated Hollow CuO/Cu2O Heterostructure Heterohedron as an Efficient Electrocatalyst for Hydrogen Evolution Reaction

It is of pivotal significance to probe highly efficient, cost-effective and low-cost catalysts for hydrogen evolution reaction. Herein, closely packed carbon-encapsulated CuO/Cu2O heterohedron with heterojunction structure is reported that combines...

Designing Self-Supported Electrocatalysts for Electrochemical Water Splitting: Surface/Interface Engineering toward Enhanced Electrocatalytic Performance

Electrochemical water splitting is regarded as the most attractive technique to store renewable electricity in the form of hydrogen fuel. However, the corresponding anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER) remain challenging, which exhibit complex reactions and sluggish kinetic behaviors at the triple-phase interface. Material surface and interface engineering provide a feasible approach to improve catalytic activity. Besides, self-supported electrocatalysts have been proven to be highly efficient toward water splitting, because of the regulated catalyst/substrate interface. In this Review, the state-of-the-art achievements in self-supported electrocatalyst for HER/OER have demonstrated the feasibility of surface and interface engineering strategies to boost performance. The six key effective surface/interface engineering approaches for rational catalysts design are systematically reviewed, including defect engineering, morphology engineering, crystallographic tailoring, heterostructure design, catalyst/substrate interface engineering, and catalyst/electrolyte interface regulation. Finally, the challenges and opportunities on the valuable directions are proposed to inspire future investigation of highly active and durable HER/OER electrocatalysts.

Improved Interface Charge Transfer and Redistribution in CuO-CoOOH p-n Heterojunction Nanoarray Electrocatalyst for Enhanced Oxygen Evolution Reaction

Electron density modulation is of great importance in an attempt to achieve highly active electrocatalysts for the oxygen evolution reaction (OER). Here, the successful construction of CuO@CoOOH p-n heterojunction (i.e., p-type CuO and n-type CoOOH) nanoarray electrocatalyst through an in situ anodic oxidation of CuO@CoSx on copper foam is reported. The p-n heterojunction can remarkably modify the electronic properties of the space-charge region and facilitate the electron transfer. Moreover, in situ Raman study reveals the generation of SO4 2- from CoSx oxidation, and electron cloud density distribution and density functional theory calculation suggest that surface-adsorbed SO4 2- can facilitate the OER process by enhancing the adsorption of OH- . The positively charged CoOOH in the space-charge region can significantly enhance the OER activity. As a result, the CuO@CoOOH p-n heterojunction shows significantly enhanced OER performance with a low overpotential of 186 mV to afford a current density of 10 mA cm-2 . The successful preparation of a large scale (14 × 25 cm2 ) sample demonstrates the possibility of promoting the catalyst to industrial-scale production. This study offers new insights into the design and fabrication of non-noble metal-based p-n heterojunction electrocatalysts as effective catalytic materials for energy storage and conversion.

Assembly of Cobalt Layered Double Hydroxide on Cuprous Phosphide Nanowire with Strong Built-In Potential for Accelerated Overall Water Splitting

Heterostructure plays an important role in boosting the overall water splitting (OWS) performance of nonprecious metal electrocatalysts. However, rational design and synthesis of semiconductor heterojunctions especially for Cu-based ones as efficient bifunctional electrocatalysts toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) still face challenges, and the in-depth study of catalytic mechanisms is urgently needed. Herein, n-type cobalt layered double hydroxide nanosheets are assembled on p-type cuprous phosphide nanowire to form p-n junction. This heterostructure with a strong built-in potential (E_BI ) of 1.78 V provides enlarged electrochemical active surface area, enhanced active site, facilitated electron separation and transfer, and accelerated formation of superoxide radical. As expected, the heterogeneous electrocatalyst exhibits significantly improved activities for OWS, achieving an overpotential of 111 mV for HER and 221 mV for OER and an applied voltage of 1.575 V for OWS at 10 mA cm^-2 in 1 m KOH. Moreover, the overpotentials are further decreased under visible light irradiation. This work represents a new insight into Cu-based catalysts toward OWS and an approach based on E_BI to design semiconductor heterostructure promising for renewable energy applications.

Peptide-Based Electrochemiluminescence Biosensors Using Silver Nanoclusters as Signal Probes and Pd-Cu2O Hybrid Nanoconcaves as Coreactant Promoters for Immunoassays

Metal nanoclusters (NCs) possess high light stability and biocompatibility because of their unique quantum size effect, which has gradually become a new type of electrochemiluminescence (ECL) nanomaterial for immunoassays. However, the luminescence efficiency of metal NCs is too low to meet the needs of trace analysis, which limits its application. Herein, Ag NCs served as signal probes and Pd-Cu₂O hybrid nanoconcaves served as coreaction promoters, developing a highly efficient peptide-based biosensor for neuron-specific enolase (NSE) detection. Utilizing the reversible cycle of Cu⁺/Cu²⁺ and the reduction characteristics of Pd NPs, Pd-Cu₂O greatly accelerates the reduction of S₂O₈^2-. Meanwhile, Pd-Cu₂O has good hydrogen evolution activity, which promotes the generation of oxygen by improving the redox efficiency of the overall reaction, thus increasing the yield of active intermediates (OH^•) to promote the reduction of S₂O₈^2-. Specially, this is an effective attempt to use the hydrogen evolution reaction (HER) to accelerate the ECL emission of the S₂O₈^2- system. In addition, a short peptide ligand (NARKFYKGC, NFC) was developed to implement the targeted immobilization of antibodies, which can specifically bind to the Fc fragment of antibodies, thereby avoiding the occupation of the antigen binding site (Fab fragment). The introduction of NFC not only improves the binding efficiency of antibodies but also protects its bioactivity, thus significantly improving the sensitivity of the biosensor. Based on these strategies, the proposed biosensor provides a new perspective for the applications of metal NCs in ECL systems.

Electron Density Modulation of MoO2/Ni to Produce Superior Hydrogen Evolution and Oxidation Activities

Hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) have aroused great interest, but the high price of platinum group metals (PGMs) limits their development. The electronic reconstruction at the interface of a heterostructure is a promising strategy to enhance their catalytic performance. Here, MoO₂/Ni heterostructure was synthesized to provide effective HER in an alkaline electrolyte and exhibit excellent HOR performance. Theoretical and experimental analyses prove that the electron density around the Ni atom is reduced. The electron density modulation optimizes the hydrogen adsorption and hydroxide adsorption free energy, which can effectively improve the activity of both HER and HOR. Accordingly, the prepared MoO₂/Ni@NF catalyst reveals robust HER activity (η₁₀ = 50.48 mV) and HOR activity (j₀ = ∼1.21 mA cm^-2). This work demonstrates an effective method to design heterostructure interfaces and tailor the surface electronic structure to improve HER/HOR performance.

Promoting Bifunctional Water Splitting by Modification of the Electronic Structure at the Interface of NiFe Layered Double Hydroxide and Ag

Electrochemical water splitting is a promising method for the renewable production of high-purity hydrogen via the hydrogen evolution reaction (HER). Ni-Fe layered double hydroxides (Ni-Fe LDHs) are highly efficient materials for mediating the oxygen evolution reaction (OER), a half-reaction for water splitting at the anode, but LDHs typically display poor HER performance. Here, we report the preparation of self-organized Ag@NiFe layered double hydroxide core-shell electrodes on Ni foam (Ag@NiFe/NF) prepared by galvanic etching for mediating both the HER and OER (bifunctional water-splitting electrocatalysis). This synthetic strategy allowed for the preparation of organized hierarchical architectures which displayed improved the electrochemical performance by tuning the electronic structure of the catalyst and increasing the surface area utilization. X-ray photoelectron spectroscopy (XPS) and theoretical calculations revealed that electron transfer from the Ni-Fe LDH to Ag influenced the adsorption of the reaction intermediates leading to enhanced catalytic activity. The Ag@NiFe/NF electrode displayed overpotentials as low as 180 and 80 mV for oxygen and hydrogen evolution, respectively, at a current density of 10 mA cm^-2, and improvements in the specific activity by ∼5× and ∼1.5× for the oxygen and hydrogen evolution reaction, respectively, compared to benchmark NiFe hydroxide materials. Additionally, an integrated water-splitting electrolyzer electrode can be driven by an AA battery.

AgCu Bimetallic Electrocatalysts for the Reduction of Biomass-Derived Compounds

The electrochemical transformation of biomass-derived compounds (e.g., aldehyde electroreduction to alcohols) is gaining increasing interest due to the sustainability of this process that can be exploited to produce value-added products from biowastes and renewable electricity. In this framework, the electrochemical conversion of 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydroxymethyl)furan (BHMF) is studied. Nanostructured Ag deposited on Cu is an active and selective electrocatalyst for the formation of BHMF in basic media. However, this catalyst deserves further research to elucidate the role of the morphology and size of the coated particles in its performance as well as the actual catalyst surface composition and its stability. Herein, Ag is coated on Cu open-cell foams by electrodeposition and galvanic displacement to generate different catalyst morphologies, deepening on the particle growth mechanism, and the samples are compared with bare Ag and Cu foams. The chemical-physical and electrochemical properties of the as-prepared and spent catalysts are correlated to the electroactivity in the HMF conversion and its selectivity toward the formation of BHMF during electroreduction. AgCu bimetallic nanoparticles or dendrites are formed on electrodeposited and displaced catalysts, respectively, whose surface is Cu-enriched along with electrochemical tests. Both types of bimetallic AgCu particles evidence a superior electroactive surface area as well as an enhanced charge and mass transfer in comparison with the bare Ag and Cu foams. These features together with a synergistic role between Ag and Cu superficial active sites could be related to the twofold enhanced selectivity of the Ag/Cu catalysts for the selective conversion of HMF to BHMF, that is, >80% selectivity and ∼ 100% conversion, and BHMF productivity values (0.206 and 0.280 mmol cm^-2 h^-1) ca. 1.5-3 times higher than those previously reported.

Electrosynthesized CuOx/graphene by a four-electrode electrolysis system for the oxygen reduction reaction to hydrogen peroxide

Here a facile four-electrode electrolysis system is firstly applied to synthesize a CuOx/graphene hybrid. The exfoliation of graphite via high electrolytic voltage and dissolution of copper via low electrolytic voltage are achieved simultaneously. CuOx/G with the highest content of CuOx shows superior electrocatalytic activity for oxygen reduction to hydrogen peroxide.

Rapid fabrication of silver–cuprous oxide core–shell nanowires for visible light photocatalysts

This work reports a novel method that enables facile fabrication of Ag–Cu₂O core–shell nanowires (Ag@Cu₂O NWs) for visible light photocatalysts.

Ni(OH)2–Ag hybrid nanosheet array with ultralow Ag loading as a highly efficient and stable electrocatalyst for hydrogen evolution reaction

0D Ag nanoparticles were successfully loaded onto 2D Ni(OH)₂ nanosheets on 3D nickel foam by a one-step hydrothermal method for enhancing the electrocatalytic ability.

Interface engineering of Ag-Ni3S2 heterostructures toward efficient alkaline hydrogen evolution

Exploring Earth-abundant transition-metal-based electrocatalysts with high performance toward the alkaline hydrogen evolution reaction (HER) is crucial for sustainable hydrogen production. Ni3S2 has been recently identified as a promising HER catalyst, but it has unfavorable water dissociation and hydrogen adsorption characteristics. Here, we report Ag-decorated Ni3S2 nanosheet arrays grown on Ni Foam (NF) (Ag-Ni3S2/NF) as efficient heterostructure electrocatalysts for the HER in alkaline media. The catalyst only requires a low overpotential of 89 mV at 10 mA cm-2, as well as sustaining long-term durability for 15 h. The experimental analysis, in combination with density functional theory calculation, demonstrates that the electronic coupling at the interface between Ni3S2 and Ag results in enhanced electronic conductivity and optimized hydrogen adsorption and water adsorption/dissociation free energies. This work not only develops a highly efficient catalyst toward the HER, but also sheds light on the structure-activity relationship of the heterostructure catalyst on an atomic scale.

Interface Engineering of Binder-Free Earth-Abundant Electrocatalysts for Efficient Advanced Energy Conversion

Gas-involved electrocatalysts for the hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction are crucial for many clean and effective energy technologies. The interface chemistry of electrocatalysts plays an important role in the optimization of their catalytic activity and stability. However, these gas-involved reactions exhibit sluggish kinetics and complex reactions at triple-phase interfaces. Thus, interface engineering at multiscale levels plays a decisive role. Binder-free electrocatalysts have gained increasing popularity, owing to their enhanced electron transfer and improved mass diffusion. This Review summarizes the influence of binder-free electrocatalysts with optimized interfaces and emphasizes three key interfaces, including the electrocatalyst/substrate interface, the inner interface of the electrocatalyst, and the electrocatalyst/electrolyte/gas interface, which are integral to determining the properties of gas-involved electrocatalysts, including the electrical conductivity, intrinsic catalytic activity, and mass transfer behavior. Finally, prospects and future challenges for the further development of binder-free electrocatalysts are discussed.

A WO3/PPy/ACF modified electrode in electrochemical system for simultaneous removal of heavy metal ion Cu2+ and organic acid

Heavy metal ions and organic acids are common pollutants in electroplating wastewater. Effective and economic treatment of such wastewater needs novel technologies. In this study, WO₃/PPy-1/ACF electrode was prepared using a hydrothermal modification method and it has large specific area (788.27 m² g^-1), high areal capacitance (2.58 F cm^-2 under 5 mA cm^-2 charge and discharge) and excellent conductivity. The modified electrode was used in an electrochemical system with activated carbon fiber felt (ACF) as counter electrode. The system simultaneously and successfully removed 97.8 % Cu²⁺ and 80.1 % citric acid (CA) from a simulated electroplating wastewater (typically 100 mg L^-1 Cu²⁺ and 800 mg L^-1 CA) in five- hour optimized operation. The influence of operating parameters (circulating inflow rate, applied voltage and influent pH) on the treatment performance was compared. There is interplay between Cu²⁺ reductive deposition and CA oxidation. The synergetic electrochemical treatment mechanism involves formation of hydrogen peroxide, free radicals, and catalytic effect of Cu species was proposed. This electrochemical system which is low-cost, easy to operate and highly efficient, may be applicable in treating acid-wash or electroplating wastewater, containing heavy-metal ions and organic acids.

Engineering the valence state of ZIF-67 by Cu2O for efficient nonenzymatic glucose detection

The valence state regulation of Co-based electrocatalysts is extremely important and greatly challenging to enhance the electrochemical performance toward glucose oxidation.

Highly enhanced bifunctional electrocatalytic activity of mixed copper–copper oxides on nickel foam via composition control

Fabricating Cu₂O–CuO and CuO directly on the conducting nickel foam resulted in highly enhanced OER and HER electrocatalytic activity in an alkaline medium, respectively.