Mesoporous Hollow Cu–Ni Alloy Nanocage from Core–Shell Cu@Ni Nanocube for Efficient Hydrogen Evolution Reaction

Insights into the pH effect on hydrogen electrocatalysis

Hydrogen electrocatalytic reactions, including the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR), play a crucial role in a wide range of energy conversion and storage technologies. However, the HER and HOR display anomalous non-Nernstian pH dependent kinetics, showing two to three orders of magnitude sluggish kinetics in alkaline media compared to that in acidic media. Fundamental understanding of the origins of the intrinsic pH effect has attracted substantial interest from the electrocatalysis community. More critically, a fundamental molecular level understanding of this effect is still debatable, but is essential for developing active, stable, and affordable fuel cells and water electrolysis technologies. Against this backdrop, in this review, we provide a comprehensive overview of the intrinsic pH effect on hydrogen electrocatalysis, covering the experimental observations, underlying principles, and strategies for catalyst design. We discuss the strengths and shortcomings of various activity descriptors, including hydrogen binding energy (HBE) theory, bifunctional theory, potential of zero free charge (pzfc) theory, 2B theory and other theories, across different electrolytes and catalyst surfaces, and outline their interrelations where possible. Additionally, we highlight the design principles and research progress in improving the alkaline HER/HOR kinetics by catalyst design and electrolyte optimization employing the aforementioned theories. Finally, the remaining controversies about the pH effects on HER/HOR kinetics as well as the challenges and possible research directions in this field are also put forward. This review aims to provide researchers with a comprehensive understanding of the intrinsic pH effect and inspire the development of more cost-effective and durable alkaline water electrolyzers (AWEs) and anion exchange membrane fuel cells (AMFCs) for a sustainable energy future.

Promoting Electrochemical Nitrate Reduction to Ammonia on Silver Nanocrystals Doped with Iron Series Elements

Electrochemical nitrate reduction to ammonia (NRA) is a promising approach to remove environmental pollutants while producing green NH3 under ambient conditions. Ag-based nanomaterials have been used in NRA but their iron series elements (Fe, Co, Ni) doping has not been explored yet. Herein, an effective and versatile doping strategy of Ag nanocrystals by iron series elements for efficient NRA is presented. Experimental results show that doping with Fe, Co or Ni can improve the NRA activity. Among the catalysts, AgCo delivers the best performance with a Faraday efficiency (FE) of 88.3 % and ammonia selectivity of 97.4 % at-0.23 V vs RHE, which is 1.9 and 6.2 times higher than that of plain Ag (46.4 % FE and 15.8 % selectivity), respectively. A highest NO3 - conversion rate of AgCo (91.8 %) is achieved, which maintains 16.4 ppm NO3 --N in 4 hours, meeting the drinking water level (~15 ppm NO3 --N). Moreover, the FE, selectivity, conversion rate of AgCo do not decay after the four consecutive cycles. It is found that Co doping can effectively induce the change of Ag d-band center for optimized NRA. This work reveals doping effects of iron series elements on Ag-based catalysts, and shows potential practical application in NRA.

Metal Alloys-Structured Electrocatalysts: Metal-Metal Interactions, Coordination Microenvironments, and Structural Property-Reactivity Relationships

Metal alloys-structured electrocatalysts (MAECs) have made essential contributions to accelerating the practical applications of electrocatalytic devices in renewable energy systems. However, due to the complex atomic structures, varied electronic states, and abundant supports, precisely decoding the metal-metal interactions and structure-activity relationships of MAECs still confronts great challenges, which is critical to direct the future engineering and optimization of MAECs. Here, this timely review comprehensively summarizes the latest advances in creating the MAECs, including the metal-metal interactions, coordination microenvironments, and structure-activity relationships. First, the fundamental classification, design, characterization, and structural reconstruction of MAECs are outlined. Then, the electrocatalytic merits and modulation strategies of recent breakthroughs for noble and non-noble metal-structured MAECs are thoroughly discussed, such as solid solution alloys, intermetallic alloys, and single-atom alloys. Particularly, unique insights into the bond interactions, theoretical understanding, and operando techniques for mechanism disclosure are given. Thereafter, the current states of diverse MAECs with a unique focus on structural property-reactivity relationships, reaction pathways, and performance comparisons are discussed. Finally, the future challenges and perspectives for MAECs are systematically discussed. It is believed that this comprehensive review can offer a substantial impact on stimulating the widespread utilization of metal alloys-structured materials in electrocatalysis.

Nanocomposite Electrocatalysts for Hydrogen Evolution Reactions (HERs) for Sustainable and Efficient Hydrogen Energy-Future Prospects

Hydrogen is considered a good clean and renewable energy substitute for fossil fuels. The major obstacle facing hydrogen energy is its efficacy in meeting its commercial-scale demand. One of the most promising pathways for efficient hydrogen production is through water-splitting electrolysis. This requires the development of active, stable, and low-cost catalysts or electrocatalysts to achieve optimized electrocatalytic hydrogen production from water splitting. The objective of this review is to survey the activity, stability, and efficiency of various electrocatalysts involved in water splitting. The status quo of noble-metal- and non-noble-metal-based nano-electrocatalysts has been specifically discussed. Various composites and nanocomposite electrocatalysts that have significantly impacted electrocatalytic HERs have been discussed. New strategies and insights in exploring nanocomposite-based electrocatalysts and utilizing other new age nanomaterial options that will profoundly enhance the electrocatalytic activity and stability of HERs have been highlighted. Recommendations on future directions and deliberations for extrapolating information have been projected.

Regulating Hollow Carbon Cage Supported NiCo Alloy Nanoparticles for Efficient Electrocatalytic Hydrogen Evolution Reaction

The NiCo alloy is one of the most promising alternatives to the noble-metal electrocatalysts for the hydrogen evolution reaction (HER); however, its performance is largely restricted by insufficient active sites and low surface area. Here, we fabricated a hierarchical hollow carbon cage supported NiCo alloy (denoted as HC NiCo/C) and a bulk NiCo alloy (denoted as NiCo) by reduction of a partially ZIF-67 etched ZIF-67@NiCo-LDH (LDH = layered double hydroxide) precursor and a fully ZIF-67 etched NiCo-LDH precursor, respectively. The as-prepared HC NiCo/C, in which the Ni₂₉Co₇₁ alloy nanocrystals with an average 6 nm size were encapsulated in graphitic carbon layers, provided a vastly increased electrochemically active surface area (ca. 13 times than the NiCo) and abundant catalytic active sites, which resulted in a higher HER performance with an overpotential of 99 mV than the 198 mV for NiCo at 10 mA cm^-2. Detailed experimental results suggested that only the HC NiCo/C possessed the active alloy surface composed of unsaturated Ni⁰ and Co⁰ atoms, and both the metal-support interaction and alloying effect influenced the electronic structure of Co and Ni in HC NiCo/C, whereas the NiCo exhibited pure Ni surface. Theoretical calculations further revealed the Ni₂₉Co₇₁ alloy surface in HC NiCo/C possessed the appropriate adsorption energy of the intermediate state (adsorbed H*). This work provided new insight into the construction of the stable small-sized bimetallic alloy nanocatalysts by regulating the reduction precursors.

Tuning CO2 Hydrogenation Selectivity through Reaction-Driven Restructuring on Cu-Ni Bimetal Catalysts

Tuning the selectivity of CO2 hydrogenation is of significant scientific interest, especially using nickel-based catalysts. Fundamental insights into CO2 hydrogenation on Ni-based catalysts demonstrate that CO is a primary intermediate, and product selectivity is strongly dependent on the oxidation state of Ni. Therefore, modifying the electronic structure of the nickel surface is a compelling strategy for tuning product selectivity. Herein, we synthesized well dispersed Cu-Ni bimetallic nanoparticles (NPs) using a simple hydrothermal method for CO selective CO2 hydrogenation. A detailed study on the monometallic (Ni and Cu) and bimetallic (CuxNi1-x) catalysts supported on γ-Al2O3 was performed to increase CO selectivity while maintaining the high reaction rate. The Cu0.5Ni0.5/γ-Al2O3 catalyst shows a high CO2 conversion and more CO product selectivity than its monometallic counterparts. The surface electronic and geometric structure of Cu0.5Ni0.5 bimetallic NPs was studied using ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ diffuse reflectance infrared Fourier-transform spectroscopy under reaction conditions. The Cu core atoms migrate toward the surface, resulting in the restructuring of the Cu@Ni core-shell structure to a Cu-Ni alloy during the reaction and functioning as the active site by enhancing CO desorption. A systematic correlation is obtained between catalytic activity from a continuous fixed-bed flow reactor and the surface electronic structural details derived from AP-XPS results, establishing the structure-activity relationship. This investigation contributes to providing a strategy for controlling CO2 hydrogenation selectivity by modifying the surface structure of bimetallic NP catalysts.

Bismuth-nickel bimetal nanosheets with a porous structure for efficient hydrogen production in neutral and alkaline media

Active and durable electrocatalysts are very important for efficient and economically sustainable hydrogen generation via electrocatalytic water splitting. A bismuth-nickel (Bi-Ni) bimetal nanosheet with a mesoporous structure was prepared via a self-template electrochemical in situ process. The Bi-Ni catalyst required overpotentials of 56 mV and 183 mV at 10 mA cm^-2 for the hydrogen evolution reaction (HER), which were close to that of commercial Pt/C in 1.0 M KOH and 1.0 M PBS (pH 7.0), respectively. The electrocatalyst maintained a steady current density during 20 h electrolysis in 1.0 M KOH and 1.0 M PBS (pH 7.0). Density functional theory (DFT) indicated that the alloying effect could induce charge transfer from the Bi atom to Ni atom and thus modulate the d-band centre of Bi-Ni nanosheets, which could efficiently accelerate H* conversion and H₂ desorption at the Ni active site. This promotes the HER kinetics. By adopting the Bi_84.8Ni_15.2 alloy as the cathode to establish a full-cell (IrO₂∥Bi_84.8Ni_15.2) for water splitting in 1.0 M KOH, the required cell voltage was 1.53 V to drive 10 mA cm^-2, which was lower than that of the IrO₂∥Pt/C electrolyzer (1.64 V@10 mA cm^-2).

Ni2 Se3 -CuSex Heterostructure as a Highly Efficient Bifunctional Electrocatalyst for Urea-Assisted Hydrogen Generation

Coupling urea oxidation reaction (UOR) with hydrogen evolution reaction (HER) is an attractive alternative anode reaction for electrochemical hydrogen generation with low energy consumption. However, the development of highly efficient bifunctional electrocatalysts is still a challenge. In this work, Ni₂ Se₃ -CuSe_x heterostructure was synthesized on copper foam (Ni₃ Se₂ @CuSe_x /CF) by electrodeposition accompanied by a selenization process. Benefiting from the abundant active sites, faster reaction kinetics, and modulated electronic structure, the self-supporting Ni₃ Se₂ @CuSe_x /CF electrode exhibited superior catalytic performance. Extremely low overpotentials of 120 and 140 mV were achieved at the current density of 100 mA cm^-2 for HER/UOR, respectively. Respectively, in HER||UOR coupled electrolyzer for H₂ generation, the Ni₃ Se₂ @CuSe_x /CF||Ni₃ Se₂ @CuSe_x /CF delivered a low cell voltage of 1.49 V to reach a high current density of 100 mA cm^-2 along with good stability, outperforming most of the other well-developed materials to date. The rational design of coupled heterostructure as bifunctional electrodes is a promising approach for energy-saving H₂ production.

Alloying at a Subnanoscale Maximizes the Synergistic Effect on the Electrocatalytic Hydrogen Evolution

Bonding dissimilar elements to provide synergistic effects is an effective way to improve the performance of metal catalysts. However, as the properties become more dissimilar, achieving synergistic effects effectively becomes more difficult due to phase separation. Here we describe a comprehensive study on how subnanoscale alloying is always effective for inter-elemental synergy. Thirty-six combinations of both bimetallic subnanoparticles (SNPs) and nanoparticles (NPs) were studied systematically using atomic-resolution imaging and catalyst benchmarking based on the hydrogen evolution reaction (HER). Results revealed that SNPs always produce greater synergistic effects than NPs, the greatest synergistic effect was found for the combination of Pt and Zr. The atomic-scale miscibility and the associated modulation of electronic states at the subnanoscale were much different from those at the nanoscale, which was observed by annular-dark-field scanning transmission electron microscopy (ADF-STEM) and X-ray photoelectron spectroscopy (XPS), respectively.

High-Efficiency Oxygen Reduction to Hydrogen Peroxide Catalyzed by Oxidized Mo2TiC2 MXene

The two-electron oxygen reduction reaction (2e−ORR) pathway electrochemical synthesis to H2O2 has the advantages of low investment and environmental protection and is considered to be a promising green method. Herein, the oxidized Mo2TiC2 MXene (O-Mo2TiC2) was successfully synthesized by a facile hydrothermal method as an electrocatalyst in electrocatalytic H2O2 production. The O-Mo2TiC2 achieved the 90% of H2O2 selectivity and 0.72 V vs. RHE of the onset potential. Moreover, O-Mo2TiC2 showed high charge transfer ability and long-term stable working ability of 40 h. This significantly enhanced electrocatalytic H2O2 production capacity is assigned the oxidation treatment of Mo2TiC2 MXene to generate more oxygen-containing groups in O-Mo2TiC2. This work provides a promising catalyst candidate for the electrochemical synthesis of H2O2.

Bi-functional 3D-NiCu-Double Hydroxide@Partially Etched 3D-NiCu Catalysts for Non-Enzymatic Glucose Detection and the Hydrogen Evolution Reaction

Hydrogen production, which is in the spotlight as a promising eco-friendly fuel, and the need for inexpensive and accurate electronic devices in the biochemistry field are important emerging technologies. However, the use of electrocatalytic devices based on expensive noble metal catalysts limits commercial applications. In recent years, to improve performance and reduce cost, electrocatalysts based on cheaper copper or nickel materials have been investigated for the non-enzymatic glucose oxidation reaction (GOR) and hydrogen evolution reaction (HER). In this study, we demonstrate a facile and easy electrochemical method of forming a cheap nickel copper double hydroxide (NiCu-DH) electrocatalyst deposited onto a three-dimensional (3D) CuNi current collector, which can effectively handle two different reactions due to its high activity for both the GOR and the HER. The as-prepared electrode has a structure comprising abundant 3D-interconnected porous dendritic walls for easy access of the electrolyte ions and highly conductive networks for fast electron transfer; additionally, it provides numerous electroactive sites. The synergistic combination of the dendritic 3D-CuNi with its abundant active sites and the self-made NiCu-DH with its excellent electrocatalytic activity toward the oxidation of glucose and HER enables use of the catalyst for both reactions. The as-prepared electrode as a glucose sensor exhibits an outstanding glucose detection limit value (0.4 μM) and a wide detection range (from 0.4 μM to 1.4 mM) with an excellent sensitivity of 1452.5 μA/cm2/mM. The electrode is independent of the oxygen content and free from chloride poisoning. Furthermore, the as-prepared electrode also requires a low overpotential of -180 mV versus reversible hydrogen electrode to yield a current density of 10 mA/cm2 with a Tafel slope of 73 mV/dec for the HER. Based on this performance, this work introduces a new paradigm for exploring cost-effective bi-functional catalysts for the GOR and HER.

High performance transition metal-based electrocatalysts for green hydrogen production

Hydrogen energy is a promising energy source that is environmentally friendly due to its long-term, large-capacity storage and low greenhouse gas emissions. However, the mass production of hydrogen is still technically difficult due to limitations in efficiency, stability, and cost, even though it can satisfy all of the current energy demands. Water splitting using an electrocatalyst is an efficient method for environmentally friendly hydrogen production, and various catalyst-related studies are being conducted for this purpose. For the last decade, transition metal-based compositions have been at the center of water splitting catalyst research. Despite numerous studies and developments, studies on transition metal-based catalysts so far still have various problems to be solved. Although excellent review papers on transition metal-based catalysts have been reported, the overall scope of transition metal-based catalysts has rarely been covered in the reports. In this review, we present the research about overall transition metal-based electrocatalysts for hydrogen production from four different categories, namely, alloys, transition-metal dichalcogenides (TMDs), layered double hydroxides (LDHs), and single-atom catalysts (SACs). The fundamental roles of metal alloying and unique electrical properties of TMDs, LDHs, and SACs are mainly discussed. Furthermore, we present the recent advances in photovoltaic-electrochemical (PV-EC) systems for sustainable hydrogen production. Finally, perspectives on the issues to be addressed in the research on transition metal-based electrocatalysts are provided.

The Influence of Nanoconfinement on Electrocatalysis

The use of nanoparticles and nanostructured electrodes are abundant in electrocatalysis. These nanometric systems contain elements of nanoconfinement in different degrees, depending on the geometry, which can have a much greater effect on the activity and selectivity than often considered. In this Review, we firstly identify the systems containing different degrees of nanoconfinement and how they can affect the activity and selectivity of electrocatalytic reactions. Then we follow with a fundamental understanding of how electrochemistry and electrocatalysis are affected by nanoconfinement, which is beginning to be uncovered, thanks to the development of new, atomically precise manufacturing and fabrication techniques as well as advances in theoretical modeling. The aim of this Review is to help us look beyond using nanostructuring as just a way to increase surface area, but also as a way to break the scaling relations imposed on electrocatalysis by thermodynamics.

Nanoengineering of Catalysts for Enhanced Hydrogen Production

Hydrogen (H2) has emerged as a sustainable energy carrier capable of replacing/complementing the global carbon-based energy matrix. Although studies in this area have often focused on the fundamental understanding of catalytic processes and the demonstration of their activities towards different strategies, much effort is still needed to develop high-performance technologies and advanced materials to accomplish widespread utilization. The main goal of this review is to discuss the recent contributions in the H2 production field by employing nanomaterials with well-defined and controllable physicochemical features. Nanoengineering approaches at the sub-nano or atomic scale are especially interesting, as they allow us to unravel how activity varies as a function of these parameters (shape, size, composition, structure, electronic, and support interaction) and obtain insights into structure–performance relationships in the field of H2 production, allowing not only the optimization of performances but also enabling the rational design of nanocatalysts with desired activities and selectivity for H2 production. Herein, we start with a brief description of preparing such materials, emphasizing the importance of accomplishing the physicochemical control of nanostructures. The review finally culminates in the leading technologies for H2 production, identifying the promising applications of controlled nanomaterials.

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.

Molybdenum oxide-iron, cobalt, copper alloy hybrid as efficient bifunctional catalyst for alkali water electrolysis

Efficient and durable non-precious catalyst for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is pivotal for practical water electrolysis toward clean hydrogen fuel. Herein, a molybdenum oxide-FeCoCu alloy hybrid (MoO_x-FeCoCu) catalyst was designed by polyoxometallate (POM) molecular cluster mediated solvothermal alcoholysis and ammonolysis of metal salts followed by pyrolytic reduction treatment. The HER efficiency is substantially enhanced by the ternary alloy component, which is more close to the benchmark Pt/C catalyst, and the HER catalytic stability is also superior to Pt/C catalyst. Moreover, the MoO_x-FeCoCu demonstrates high catalytic efficiency and rather good durability for OER. Benefitted by the bifunctional catalytic behaviors for HER and OER, the symmetric water electrolyzer based on the MoO_x-FeCoCu electrode requires a low driving voltage of 1.69 V to deliver a response current density of 10 mA cm^-2, which is comparable to that based on the benchmark Pt/C HER cathode and RuO₂ OER anode. The current work offers a feasible way to design efficient bifunctional catalyst for water electrolysis via POM mediated co-assembly and calcination treatment.

Self-supported efficient hydrogen evolution catalysts with a core-shell structure designed via phase separation

The development of cost-effective, high-performance and flexible electrocatalysts for hydrogen production is of scientific and technological importance. Catalysts with a core-shell structure for water dissociation have been extensively investigated. However, most of them are nanoparticles and thus their catalytic properties are inevitably limited by the use of binders in practice. Herein, this work reports a physical-metallurgy-based structural design strategy to develop a self-supported and unique nanoporous structure with core-shell-like ligaments, i.e., a Cu core surrounded by a NiO shell, formed on a metallic glass (MG) substrate. These newly developed noble metal-free catalysts exhibit outstanding HER performance; the overpotential reaches 67 mV at a current density of 10 mA cm^-2, accompanied by a low Tafel slope of 40 mV dec^-1 and good durability. More importantly, the current strategy could be readily applied to fabricate other nanoporous metals, which opens a new space for designing advanced catalysts as cost-effective electrode materials.

l-Lysine derived fabrication of Cu@Ni core–satellite nanoassemblies as efficient non-Pt catalysts for the methanol oxidation reaction

With assistance of l-lysine, Cu@Ni core–satellite nanoassemblies were fabricated, which could serve as efficient non-Pt electrocatalysts for the methanol oxidation reaction due to both the component effects and structural features.

Conductive CuCo-Based Bimetal Organic Framework for Efficient Hydrogen Evolution

Metal-organic frameworks (MOFs) with intrinsically porous structures and well-dispersed metal sites are promising candidates for electrocatalysis; however, the catalytic efficiencies of most MOFs are significantly limited by their impertinent adsorption/desorption energy of intermediates formed during electrocatalysis and very low electrical conductivity. Herein, Co is introduced into conductive Cu-catecholate (Cu-CAT) nanorod arrays directly grown on a flexible carbon cloth for hydrogen evolution reaction (HER). Electrochemical results show that the Co-incorporated Cu-CAT nanorod arrays only need 52 and 143 mV overpotentials to drive a current density of 10 mA cm^-2 in alkaline and neutral media for HER, respectively, much lower than most of the reported non-noble metal-based electrocatalysts and comparable to the benchmark Pt/C electrocatalyst. Density functional theory calculations show that the introduction of Co can optimize the adsorption energy of hydrogen (ΔG_H* ) of Cu sites, almost close to that of Pt (111). Furthermore, the adsorption energy of water ( Δ E H 2 O ) of Co sites in the CuCo-CAT is significantly lower than that of Cu sites upon coupling Cu with Co, effectively accelerating the Volmer step in the HER process. The findings, synergistic effect of bimetals, open a new avenue for the rational design of highly efficient MOF-based electrocatalysts.

Highly efficient sub-nanometer RuxCuyP2 nanoclusters designed for hydrogen evolution under alkaline media

Design of highly active and stable non-precious electrocatalysts towards hydrogen evolution reaction (HER) is a hot research topic in low cost, clean and sustainable hydrogen energy field, yet remaining the important challenge caused by the sluggish reaction kinetics for water-alkali electrolyzers. Herein, a robust electrocatalyst is proposed by designing a novel sub-nanometer of copper and ruthenium bimetallic phosphide nanoclusters (Ru_xCu_yP₂) supported on a graphited carbon nanofibers (CNF). Uniform Ru_xCu_yP₂ (~1.90 nm) on the surface of CNF are obtained by introducing the dispersed Ru, thereby improving the intrinsic activity for HER. On optimizing the Ru ratio, the (x = y = 1) RuCuP₂/CNF catalyst exhibits an excellent HER electroactivity with an overpotential of 10 mV in 1.0 M NaOH electrolyte to produce 10 mA cm^-2 current density, which is lower than commercial 20% Pt/C in alkaline solution. Moreover, the kinetic study demonstrated that electrochemical activation energies for HER of RuCuP₂/CNF is 20.7 kJ mol^-1 highest among different ratio bimetallic phosphide. This simple, cost-effective, and environmentally friendly methodology can pave the way for exploitation of bimetallic phosphide nanoclusters for catalyst design.

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.

3D Carbon Networks: Design and Applications in Sodium Ion Batteries

As the key component of a new generation for low-cost energy storage systems, sodium-ion batteries (SIBs) have attracted enormous attention and research due to its promising potentiality in large-scale electrochemical energy storage. For practical application of SIBs, carbonaceous materials have been considered to be one of the best choices for electrodes in virtue of their abundant reserves, low cost, easy availability, and environmental friendliness. 3D carbon network (3D-carbon) is of particular interests, which has displayed outstanding features, including abundant active sites, interconnected multi-level pore structures, high electronic conductivity, and excellent mechanical stability. Herein, we review the structural advantages of 3D-carbon and its preparation methods, and then discuss recent progress in 3D carbon materials and their composites for SIBs. The superior functionalities of 3D-carbon are emphasized as support templates or encapsulation shell membranes. Finally, we summarize and outline the challenges and future prospects of 3D-carbon in SIBs.

Gd-Doped Ni-Oxychloride Nanoclusters: New Nanoscale Electrocatalysts for High-Performance Water Oxidation through Surface and Structural Modification

Oxygen evolution reaction (OER) is a bottleneck process in the water-splitting module for sustainable and clean energy production. Transition metal-based electrocatalysts can be effective as water-splitting catalytic materials because of their appropriate redox properties and natural abundance, but the slow kinetics because of strong adsorption and consequently slow desorption of intermediates on the active sites of catalysts severely hamper the dynamics of the released molecular oxygen and thus remains a formidable challenge. Herein, we report the development of structurally and surface-modified PA-Gd-Ni(OH)₂Cl (partially alkylated gadolinium-doped nickel oxychloride) nanoclusters (NCs, size ≤ 3 nm) for enhanced and stable OER catalysis at low overpotential and high turnover frequency. The ameliorated catalytic performance was achieved by controlling the surface coverage of these NCs with hydrophobic ligands and through the incorporation of electronegative atoms to facilitate easy adsorption/desorption of intermediates on the catalyst surface, thus improving the liberation of O₂. Such a surface and structural modification and uniform distribution at the nanoscale length are indeed worth considering to selectively tune the catalytic potential and further modernize the electrode materials for the challenging OER process.

Interface Engineering of Co-LDH@MOF Heterojunction in Highly Stable and Efficient Oxygen Evolution Reaction

The electrochemical splitting of water into hydrogen and oxygen is considered one of the most promising approaches to generate clean and sustainable energy. However, the low efficiency of the oxygen evolution reaction (OER) acts as a bottleneck in the water splitting process. Herein, interface engineering heterojunctions between ZIF-67 and layered double hydroxide (LDH) are designed to enhance the catalytic activity of the OER and the stability of Co-LDH. The interface is built by the oxygen (O) of Co-LDH and nitrogen (N) of the 2-methylimidazole ligand in ZIF-67, which modulates the local electronic structure of the catalytic active site. Density functional theory calculations demonstrate that the interfacial interaction can enhance the strength of the Co-Oout bond in Co-LDH, which makes it easier to break the H-Oout bond and results in a lower free energy change in the potential-determining step at the heterointerface in the OER process. Therefore, the Co-LDH@ZIF-67 exhibits superior OER activity with a low overpotential of 187 mV at a current density of 10 mA cm-2 and long-term electrochemical stability for more than 50 h. This finding provides a design direction for improving the catalytic activity of OER.

Understanding the influence of experimental factors on bio-interactions of nanoparticles: Towards improving correlation between in vitro and in vivo studies

Bionanotechnology has developed rapidly over the past two decades, owing to the extensive and versatile, functionalities and applicability of nanoparticles (NPs). Fifty-one nanomedicines have been approved by FDA since 1995, out of the many NPs based formulations developed to date. The general conformation of NPs consists of a core with ligands coating their surface, that stabilizes them and provides them with added functionalities. The physicochemical properties, especially the surface composition of NPs influence their bio-interactions to a large extent. This review discusses recent studies that help understand the nano-bio interactions of iron oxide and gold NPs with different surface compositions. We discuss the influence of the experimental factors on the outcome of the studies and, thus, the importance of standardization in the field of nanotechnology. Recent studies suggest that with careful selection of experimental parameters, it is possible to improve the positive correlation between in vitro and in vivo studies. This provides a fundamental understanding of the NPs which helps in assessing their potential toxic side effects and may aid in manipulating them further to improve their biocompatibility and biosafety.

Shaping non-noble metal nanocrystals via colloidal chemistry

Non-noble metal nanocrystals with well-defined shapes have been attracting increasingly more attention in the last decade as potential alternatives to noble metals, by virtue of their earth abundance combined with intriguing physical and chemical properties relevant for both fundamental studies and technological applications. Nevertheless, their synthesis is still primitive when compared to noble metals. In this contribution, we focus on third row transition metals Mn, Fe, Co, Ni and Cu that are recently gaining interest because of their catalytic properties. Along with providing an overview on the state-of-the-art, we discuss current synthetic strategies and challenges. Finally, we propose future directions to advance the synthetic development of shape-controlled non-noble metal nanocrystals in the upcoming years.

Cu@Ni core-shell nanoparticles prepared via an injection approach with enhanced oxidation resistance for the fabrication of conductive films

Building core-shell structures is a valuable method of enhancing the oxidation-resistance performance of Cu nanoparticles for practical applications in the field of printed circuit boards. In this study, Cu@Ni core-shell nanoparticles are synthesized via an injection solution approach utilizing Cu seeds produced during the reactions to induce the epitaxial growth of Ni shells. The thickness of the Ni shell can be controlled by varying the Cu:Ni molar ratios in the injected precursor solution, whereas changing the injection rate of the Cu precursor solution affects the size of the Cu seeds and thus controls the eventual size of the core-shell nanoparticles. Thermogravimetric analysis reveals a superior thermal stability against oxidation for Cu@Ni core-shell nanoparticles, as compared with Cu nanoparticles. The oxidation resistance of Cu@Ni conductive films increases with an increase in the Ni:Cu ratio, while the conductivity increases with a decrease in the Ni:Cu ratio. A relatively low resistivity of 27.4 µΩ cm is achieved for Cu@Ni conductive films. The results demonstrate that coating Cu nanoparticles with Ni shells via epitaxial growth can form closed shells with smooth surfaces which are valuable for Cu nanoparticles in applications where oxidation resistance is a requirement .

Ultra-small hollow ternary alloy nanoparticles for efficient hydrogen evolution reaction

Hollow nanoparticles with large specific surface area and high atom utilization are promising catalysts for the hydrogen evolution reaction (HER). We describe herein the design and synthesis of a series of ultra-small hollow ternary alloy nanostructures using a simple one-pot strategy. The same technique was demonstrated for hollow PtNiCu nanoparticles, hollow PtCoCu nanoparticles and hollow CuNiCo nanoparticles. During synthesis, the displacement reaction and oxidative etching played important roles in the formation of hollow structures. Moreover, our hollow PtNiCu and PtCoCu nanoparticles were single crystalline, with an average diameter of 5 nm. Impressively, ultra-small hollow PtNiCu nanoparticles, containing only 10% Pt, exhibited greater electrocatalytic HER activity and stability than a commercial Pt/C catalyst. The overpotential of hollow PtNiCu nanoparticles at 10 mA cm^-2 was 28 mV versus reversible hydrogen electrode (RHE). The mass activity was 4.54 A mg_Pt ^-1 at -70 mV versus RHE, which is 5.62-fold greater than that of a commercial Pt/C system (0.81 A mg_Pt ^-1). Through analyses of bonding and antibonding orbital filling, density functional theory calculations demonstrated that the bonding strength of different metals to the hydrogen intermediate (H^*) was in the order of Pt > Co > Ni > Cu. The excellent HER performance of our hollow PtNiCu nanoparticles derives from moderately synergistic interactions between the three metals and H^*. This work demonstrates a new strategy for the design of low-cost and high-activity HER catalysts.

Core-shell nanostructured electrocatalysts for water splitting

As the cornerstone of the hydrogen economy, water electrolysis consisting of the hydrogen and oxygen evolution reactions (HER and OER) greatly needs cost-efficient electrocatalysts that can decrease the dynamic overpotential and save on energy consumption. Over past years, observable progress has been made by constructing core-shell structures free from or with few noble-metals. They afford particular merits, e.g., a highly-exposed active surface, modulated electronic configurations, strain effects, interfacial synergy, or reinforced stability, to promote the kinetics and electrocatalytic performance of the HER, OER and overall water splitting. So far, a large variety of inorganics (carbon and transition-metal related components) have been introduced into core-shell electrocatalysts. Herein, representative efforts and progress are summarized with a clear classification of core and shell components, to access comprehensive insights into electrochemical processes that proceed on surfaces or interfaces. Finally, a perspective on the future development of core-shell electrocatalysts is offered. The overall aim is to shed some light on the exploration of emerging materials for energy conversion and storage.

Metal–organic framework derived nitrogen-doped carbon-RhNi alloys anchored on graphene for highly efficient hydrogen evolution reaction

Nitrogen-doped carbon-RhNi alloy nanoparticles anchored on reduced graphene oxide nanosheet hybrid structure (NC-RhNi/rGO) exhibit high HER performance.

Direct Growth of Highly Strained Pt Islands on Branched Ni Nanoparticles for Improved Hydrogen Evolution Reaction Activity

The direct growth of Pt islands on lattice mismatched Ni nanoparticles is a major synthetic challenge and a promising strategy to create highly strained Pt atoms for electrocatalysis. By using very mild reaction conditions, Pt islands with tunable strain were formed directly on Ni branched particles. The highly strained 1.9 nm Pt-island on branched Ni nanoparticles exhibited high specific activity and the highest mass activity for hydrogen evolution (HER) in a pH 13 electrolyte. These results show the ability to synthetically tune the size of the Pt islands to control the strain to give higher HER activity.