Platinum-nickel alloy excavated nano-multipods with hexagonal close-packed structure and superior activity towards hydrogen evolution reaction

Optimizing Interfacial Charge Dynamics and Quantum Effects in Heterodimensional Superlattices for Efficient Hydrogen Production

Superlattice materials have emerged as promising candidates for water electrocatalysis due to their tunable crystal structures, electronic properties, and potential for interface engineering. However, the catalytic activity of transition metal-based superlattice materials for the hydrogen evolution reaction (HER) is often constrained by their intrinsic electronic band structures, which can limit charge carrier mobility and active site availability. Herein, a highly efficient electrocatalyst based on a VS2-VS heterodimensional (2D-1D) superlattice with sulfur vacancies is designed addressing the limitations posed by the intrinsic electronic structure. The enhanced catalytic performance of the VS2-VS superlattice is primarily attributed to the engineered heterojunction, where the work function difference between the VS2 layer and VS chain induces a charge separation field that promotes efficient electron-hole separation. Introducing sulfur vacancies further amplifies this effect by inducing quantum localization of the separated electrons, thereby significantly boosting HER activity. Both theoretical and experimental results demonstrate that the superlattice achieves a ΔGH* of -0.06 eV and an impressively low overpotential of 46 mV at 10 mA·cm-2 in acidic media, surpassing the performance of commercial Pt/C while maintaining exceptional stability over 15 000 cycles. This work underscores the pivotal role of advanced material engineering in designing catalysts for sustainable energy applications.

NiIr Nanowire Assembles as an Efficient Electrocatalyst Towards Oxygen Evolution Reaction in Both Acid and Alkaline Media

Oxygen evolution reaction (OER) is the rate-limiting step in water electrolysis due to its sluggish kinetic, and it is challenging to develop an OER catalyst that could work efficiently in both acid and alkaline environment. Herein, NiIr nanowire assembles (NAs) with unique nanoflower morphology were prepared by a facile hydrothermal method. As a result, the NiIr NAs exhibited superior OER activity in both acid and alkaline media. Specifically, in 0.1 M HClO4, NiIr NAs presented a superior electrocatalytic performance with a low overpotential of merely 242 mV at 10 mA cm-2 and a Tafel slope of only 58.1 mV dec-1, surpassing that of commercial IrO2 and pure Ir NAs. And it achieved a significantly higher mass activity of 148.40 A/g at -1.5 V versus RHE. In 1.0 M KOH, NiIr NAs has an overpotential of 291 mV at 10 mA cm-2 and a Tafel slope of 42.1 mV dec-1. Such remarkable activity makes the NiIr NAs among the best of recently reported representative Ir-based OER electrocatalysts. Density functional theory (DFT) calculations confirmed alloying effect promotes surface bonding of NiIr with oxygen-containing reactants, resulting in excellent catalytic properties.

S-S Bond Strategy at Sulfide Heterointerface: Reversing Charge Transfer and Constructing Hydrogen Spillover for Boosted Hydrogen Evolution

Developing efficient electrocatalyst in sulfides for hydrogen evolution reaction (HER) still poses challenges due to the lack of understanding the role of sulfide heterointerface. Here, we report a sulfide heterostructure RuSx/NbS2, which is composed of 3R-type NbS2 loaded by amorphous RuSx nanoparticles with S-S bonds formed at the interface. As HER electrocatalyst, the RuSx/NbS2 shows remarkable low overpotential of 38 mV to drive a current density of 10 mA cm-2 in acid, and also low Tafel slope of 51.05 mV dec-1. The intrinsic activity of RuSx/NbS2 is much higher than that of Ru/NbS2 reference as well as the commercial Pt/C. Both experiments and theoretical calculations unveil a reversed charge transfer at the interface from NbS2 to RuSx that driven by the formation of S-S bonds, resulting in electron-rich Ru configuration for strong hydrogen adsorption. Meanwhile, electronic redistribution induced by the sulfide heterostructure facilitates hydrogen spillover (HSo) effect in this system, leading to accelerated hydrogen desorption at the basal plane of NbS2. This study provides an effective S-S bond strategy in sulfide heterostructure to synergistically modulate the charge transfer and adsorption thermodynamics, which is very valuable for the development of efficient electrocatalysts in practical applications.

Optimizing Surface State Electrons of Topological Semi-Metal by Atomic Doping for Enhanced Hydrogen Evolution Reaction

Topological materials carrying topological surface states (TSSs) have extraordinary carrier mobility and robustness, which provide a new platform for searching for efficient hydrogen evolution reaction (HER) electrocatalysts. However, the majority of these TSSs originate from the sp band of topological quantum catalysts rather than the d band. Here, based on the density functional theory calculation, it is reported a topological semimetal Pd3Sn carrying TSSs mainly derived from d orbital and proposed that optimizing surface state electrons of Pd3Sn by introduction heteroatoms (Ni) can promote hybridization between hydrogen atoms and electrons, thereby reducing the Gibbs free energy (ΔGH) of adsorbed hydrogen and improving its HER performance. Moreover, this is well verified by electrocatalytic experiment results, the Ni-doped Pd3Sn (Ni0.1Pd2.9Sn) show much lower overpotential (-29 mV vs RHE) and Tafel slope (17 mV dec-1) than Pd3Sn (-39 mV vs RHE, 25 mV dec-1) at a current density of 10 mA cm-2. Significantly, the Ni0.1Pd2.9Sn nanoparticles exhibit excellent stability for HER. The electrocatalytic activity of Ni0.1Pd2.9Sn nanoparticles is superior to that of commercial Pt. This work provides an accurate guide for manipulating surface state electrons to improve the HER performance of catalysts.

Surficial Reconstruction of Pt-Ni/NiS and Its Effect on Electrocatalytic Hydrogen Evolution in Alkaline Medium

Cyclic voltammetry pretreatment of Pt-based electrocatalysts has been proven to be a normal activation process on achieving the optimal alkaline hydrogen evolution performance. Until now, the congruent relationship between the microstructural evolution and performance improvement during this process has rarely been reported. Herein, when the in situ transmission electron microscopy and in situ Raman analyses are employed, a self-reconstruction process from crystalline NiS into amorphous nickel hydroxide hydrate [Ni(OH)2-x·H2O, where x ≈ 0.3] on the surface of platinum-nickel nanowires has first been captured, which is the critical water dissociation active site to offer a sufficient proton supply. Furthermore, such a surficial reconstruction triggers an increase in the current density from -2.3 to -38.8 mA/cm2 (at -70 mV), which is nearly 17 times. These observations point to the fact that it is essential to consider the fundamental mechanisms of hydrogen evolution on the active sites when the process is scaled up.

Site-Selective Growth of fcc-2H-fcc Copper on Unconventional Phase Metal Nanomaterials for Highly Efficient Tandem CO2 Electroreduction

Copper (Cu) nanomaterials are a unique kind of electrocatalysts for high-value multi-carbon production in carbon dioxide reduction reaction (CO2RR), which holds enormous potential in attaining carbon neutrality. However, phase engineering of Cu nanomaterials remains challenging, especially for the construction of unconventional phase Cu-based asymmetric heteronanostructures. Here the site-selective growth of Cu on unusual phase gold (Au) nanorods, obtaining three kinds of heterophase fcc-2H-fcc Au-Cu heteronanostructures is reported. Significantly, the resultant fcc-2H-fcc Au-Cu Janus nanostructures (JNSs) break the symmetric growth mode of Cu on Au. In electrocatalytic CO2RR, the fcc-2H-fcc Au-Cu JNSs exhibit excellent performance in both H-type and flow cells, with Faradaic efficiencies of 55.5% and 84.3% for ethylene and multi-carbon products, respectively. In situ characterizations and theoretical calculations reveal the co-exposure of 2H-Au and 2H-Cu domains in Au-Cu JNSs diversifies the CO* adsorption configurations and promotes the CO* spillover and subsequent C-C coupling toward ethylene generation with reduced energy barriers.

Platinum Cluster Decoration on Hollow Carbon Spheres for High-Efficiency Hydrogen Evolution Reaction

Currently, platinum (Pt)/carbon support composite materials have tremendous application prospects in the hydrogen evolution reaction (HER). However, one of the primary challenges for boosting their performance is designing a substrate with the desired microstructure. Herein, the intact hollow carbon spheres (HCSs) were prepared via template method. Based on the morphology variation of the as-prepared HCSs-x, we conjectured that the polydopamine (PDA) core was generated first and then slowly grew into a complete overburden (SiO2@PDA). Afterward, Pt atomic clusters were anchored on the outer shells of HCSs-4 to construct composite electrocatalysts (Pty/HCSs-4) by a chemical reduction method. Due to the low charge-transfer resistance, the HCSs have a large electrochemical surface area and provide a continuous electron transport pathway, boosting the atom utilization efficiency during hydrogen production and release. The synthesized Pt2.5/HCSs-4 electrocatalysts exhibit excellent HER activity in acidic media, which can be ascribed to the compositional modulation and delicate structural design. Specifically, when the overpotential is 10 A g-1, the overpotential can achieve 92 mV. This work opens a new route to fabricate Pt-based electrocatalysts and brings a new understanding of the formation mechanism of HCSs.

Controlled Synthesis of Unconventional Phase Alloy Nanobranches for Highly Selective Electrocatalytic Nitrite Reduction to Ammonia

The controlled synthesis of metal nanomaterials with unconventional phases is of significant importance to develop high-performance catalysts for various applications. However, it remains challenging to modulate the atomic arrangements of metal nanomaterials, especially the alloy nanostructures that involve different metals with distinct redox potentials. Here we report the general one-pot synthesis of IrNi, IrRhNi and IrFeNi alloy nanobranches with unconventional hexagonal close-packed (hcp) phase. Notably, the as-synthesized hcp IrNi nanobranches demonstrate excellent catalytic performance towards electrochemical nitrite reduction reaction (NO2RR), with superior NH3 Faradaic efficiency and yield rate of 98.2 % and 34.6 mg h-1 mgcat -1 (75.5 mg h-1 mgIr -1) at 0 and -0.1 V (vs reversible hydrogen electrode), respectively. Ex/in situ characterizations and theoretical calculations reveal that the Ir-Ni interactions within hcp IrNi alloy improve electron transfer to benefit both nitrite activation and active hydrogen generation, leading to a stronger reaction trend of NO2RR by greatly reducing energy barriers of rate-determining step.

Analyzing the Active Site and Predicting the Overall Activity of Alloy Catalysts

As one of the potential catalysts, disordered solid solution alloys can offer a wealth of catalytic sites. However, accurately evaluating their activity localization structure and overall activity from each individual site remains a formidable challenge. Herein, an approach based on density functional theory and machine learning was used to obtain a large number of sites of the Pt-Ru alloy as the model multisite catalyst for the hydrogen evolution reaction. Subsequently, a series of statistical approaches were employed to unveil the relationship between the geometric structure and overall activity. Based on the radial frequency distribution of metal elements and the distribution of ΔGH, we have identified the surface and subsurface sites occupied by Pt and Ru, respectively, as the most active sites. Particularly, the concept of equivalent site ratio predicts that the overall activity is highest when the Ru content is 20-30%. Furthermore, a series of Pt-Ru alloys were synthesized to validate the proposed theory. This provides crucial insights into understanding the origin of catalytic activity in alloys and thus will better guide the rational development of targeted multisite catalysts.

Mixed-Dimensional Partial Dealloyed PtCuBi/C as High-Performance Electrocatalysts for Methanol Oxidation with Enhanced CO Tolerance

Developing efficient electrocatalysts for methanol oxidation reaction (MOR) is crucial in advancing the commercialization of direct methanol fuel cells (DMFCs). Herein, carbon-supported 0D/2D PtCuBi/C (0D/2D PtCuBi/C) catalysts are fabricated through a solvothermal method, followed by a partial electrochemical dealloying process to form a novel mixed-dimensional electrochemically dealloyed PtCuBi/C (0D/2D D-PtCuBi/C) catalysts. Benefiting from distinctive mixed-dimensional structure and composition, the as-obtained 0D/2D D-PtCuBi/C catalysts possess abundant accessible active sites. The introduction of Cu as a water-activating element weakens the COads, and oxophilic metal Bi facilitates the OHads, thereby enhancing its tolerance to CO poisoning and promoting MOR activity. The X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS) collectively reveal the electron transfer from Cu and Bi to Pt, the electron-enrichment effect induced by dealloying, and the strong interactions among Pt-M (Cu, Pt, and Bi) multi-active sites, which improve the tuning of the electronic structure and enhancement of electron transfer ability. Impressively, the optimized 0D/2D D-PtCuBi/C catalysts exhibit the superior mass activity (MA) of 17.68 A mgPt -1 for MOR, which is 14.86 times higher than that of commercial Pt/C. This study offers a proposed strategy for Pt-based alloy catalysts, enabling their use as efficient anodic materials in fuel cell applications.

Cu Tailoring Pt Enables Branched-Structured Electrocatalysts with High Concave Surface Curvature Toward Efficient Methanol Oxidation

Surface engineering offers opportunities for the design and synthesis of Pt-based alloyed electrocatalysts with high mass activity and resistance to CO poisoning, which is of great significance for methanol electrooxidation. Surface curvature regulation may endow electrocatalysts with enhanced atomic utilization and abundance of unsaturated atoms; however, a reliable synthetic route for controlled construction of tailorable curved surface is still lacking. Here, a colloidal-chemical method to synthesize two types of PtCu branched-structured electrocatalysts, where the concave curvature can be customized is reported. These studies show that, among various synthesis parameters, the concentration of CuCl2·2H2O precursor is the key factor in manipulating the reaction kinetics and determining the concave surface curvature. Significantly, PtCu branched nanocrystals with long and sharp arms (PtCu BNCs-L), featuring a high concave surface curvature, exhibit remarkable activity and stability toward MOR, which is mainly attributed to advanced features of a highly concave surface and the synergistically bifunctional effect from introduced oxophilic Cu metal. In situ Raman spectroscopy and CO stripping test demonstrates weakened CO adsorption and accelerated CO removal on PtCu BNCs-L. This work highlights the importance of surface curvature, opening up an appealing route for the design and synthesis of advanced electrocatalysts with well-defined surface configurations.

Crystal Phase Engineering of Ultrathin Alloy Nanostructures for Highly Efficient Electroreduction of Nitrate to Ammonia

Electrocatalytic nitrate reduction reaction (NO3RR) toward ammonia synthesis is recognized as a sustainable strategy to balance the global nitrogen cycle. However, it still remains a great challenge to achieve highly efficient ammonia production due to the complex proton-coupled electron transfer process in NO3RR. Here, the controlled synthesis of RuMo alloy nanoflowers (NFs) with unconventional face-centered cubic (fcc) phase and hexagonal close-packed/fcc heterophase for highly efficient NO3RR is reported. Significantly, fcc RuMo NFs demonstrate high Faradaic efficiency of 95.2% and a large yield rate of 32.7 mg h-1 mgcat -1 toward ammonia production at 0 and -0.1 V (vs reversible hydrogen electrode), respectively. In situ characterizations and theoretical calculations have unraveled that fcc RuMo NFs possess the highest d-band center with superior electroactivity, which originates from the strong Ru─Mo interactions and the high intrinsic activity of the unconventional fcc phase. The optimal electronic structures of fcc RuMo NFs supply strong adsorption of key intermediates with suppression of the competitive hydrogen evolution, which further determines the remarkable NO3RR performance. The successful demonstration of high-performance zinc-nitrate batteries with fcc RuMo NFs suggests their substantial application potential in electrochemical energy supply systems.

Dual-Modal Colorimetric and Surface-Enhanced Raman Scattering (SERS)-Based Lateral Flow Immunoassay for Ultrasensitive Detection of SARS-CoV-2 Using a Plasmonic Gold Nanocrown

The 2019 coronavirus disease (COVID-19) outbreak created an unprecedented need for rapid, sensitive, and cost-effective point-of-care diagnostic tests to prevent and mitigate the spread of the SARS-CoV-2 virus. Herein, we demonstrated an advanced lateral flow immunoassay (LFIA) platform with dual-functional [colorimetric and surface-enhanced Raman scattering (SERS)] detection of the spike 1 (S1) protein of SARS-CoV-2. The nanosensor was integrated with a specially designed core-gap-shell morphology consisting of a gold shell decorated with external nanospheres, a structure referred to as gold nanocrown (GNC), labeled with a Raman reporter molecule 1,3,3,1',3',3'-hexamethyl-2,2'-indotricarbocyanine iodide (HITC) to produce a strong colorimetric signal as well as an enhanced SERS signal. Among the different plasmonics-active GNC nanostructures, the GNC-2 morphology, which has a shell decorated with an optimum number and size of nanospheres, produces an intense dark-blue colorimetric signal and ultrahigh SERS signal. The limit of detection (LOD) of the S1 protein via colorimetric detection LFIA was determined to be 91.24 pg/mL. On the other hand, the LOD for the SERS LFIA method was more than three orders of magnitude lower at 57.21 fg/mL. Furthermore, we analyzed the performance of the GNC-2 nanosensor for directly analyzing the S1 protein spiked in saliva samples without any sample pretreatment and achieving the LOD as low as 39.65 fg/mL using SERS-based plasmonics-enhanced LFIA, indicating ultrahigh detection sensitivity. Overall, our GNC nanosensor showed excellent sensitivity, reproducibility, and rapid detection of the SARS-CoV-2 S1 protein, demonstrating excellent potential as a promising point-of-care platform for the early detection of respiratory virus infections.

Enhanced d-π overlap in a graphene supported Ni/PtNi heterojunction for efficient seawater hydrogen evolution

d-π overlap, which represents overlap between metal-d and graphene-π orbitals to facilitate electron transfer, has rarely been reported. Ni/PtNi-G2 exhibits exceptional performance in seawater hydrogen evolution due to the electron-rich surface on Pt resulting from enhanced d-π overlap and subsequent electron transfer from graphene and Ni to Pt.

Rapid High-Temperature Liquid Shock Synthesis of High-Entropy Alloys for Hydrogen Evolution Reaction

High-entropy-alloy nanoparticles (HEA-NPs) show great potential as electrocatalysts for water splitting, fuel cells, CO2 conversion, etc. However, fine-tuning the surface, morphology, structure, and crystal phase of HEA remains a great challenge. Here, the high-temperature liquid shock (HTLS) technique is applied to produce HEA-NPs, e.g., PtCoNiRuIr HEA-NPs, with tunable elemental components, ultrafine particle size, controlled crystal phases, and lattice strains. HTLS directly applied Joule heating on the liquid mixture of metal precursors, capping agents, and reducing agents, which is feasible for controlling the morphology and structure such as the atomic arrangement of the resulting products, thereby facilitating the rationally designed nanocatalysts. Impressively, the as-obtained PtCoNiRuIr HEA-NPs delivered superior activity and long-term stability for the hydrogen evolution reaction (HER), with low overpotentials at 10 mA cm-2 and 1 A cm-2 of only 18 and 408 mV, respectively, and 10000 CV stable cycles in 0.5 M H2SO4. Furthermore, in the near future, by combining the HTLS method with artificial intelligence (AI) and theoretical calculations, it is promising to provide an advanced platform for the high-throughput synthesis of HEA nanocatalysts with optimized performance for various energy applications, which is of great significance for achieving a carbon-neutral society with an effective and environmentally friendly energy system.

Dynamic coordination engineering of 2D PhenPtCl2 nanosheets for superior hydrogen evolution

Exploring the dynamic structural evolution of electrocatalysts during reactions represents a fundamental objective in the realm of electrocatalytic mechanism research. In pursuit of this objective, we synthesized PhenPtCl2 nanosheets, revealing a N2-Pt-Cl2 coordination structure through various characterization techniques. Remarkably, the electrocatalytic performance of these PhenPtCl2 nanosheets for hydrogen evolution reaction (HER) surpasses that of the commercial Pt/C catalyst across the entire pH range. Furthermore, our discovery of the dynamic coordination changes occurring in the N2-Pt-Cl2 active sites during the electrocatalytic process, as clarified through in situ Raman and X-ray photoelectron spectroscopy, is particularly noteworthy. These changes transition from Phen-Pt-Cl2 to Phen-Pt-Cl and ultimately to Phen-Pt. The Phen-Pt intermediate plays a pivotal role in the electrocatalytic HER, dynamically coordinating with Cl- ions in the electrolyte. Additionally, the unsaturated, two-coordinated Pt within Phen-Pt provides additional space and electrons to enhance both H+ adsorption and H2 evolution. This research illuminates the intricate dynamic coordination evolution and structural adaptability of PhenPtCl2 nanosheets, firmly establishing them as a promising candidate for efficient and tunable electrocatalysts.

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.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

Optimizing Pt-Based Alloy Electrocatalysts for Improved Hydrogen Evolution Performance in Alkaline Electrolytes: A Comprehensive Review

The splitting of water through electrocatalysis offers a sustainable method for the production of hydrogen. In alkaline electrolytes, the lack of protons forces water dissociation to occur before the hydrogen evolution reaction (HER). While pure Pt is the gold standard electrocatalyst in acidic electrolytes, since the 5d orbital in Pt is nearly fully occupied, when it overlaps with the molecular orbital of water, it generates a Pauli repulsion. As a result, the formation of a Pt-H* bond in an alkaline environment is difficult, which slows the HER and negates the benefits of using a pure Pt catalyst. To overcome this limitation, Pt can be alloyed with transition metals, such as Fe, Co, and Ni. This approach has the potential not only to enhance the performance but also to increase the Pt dispersion and decrease its usage, thus overall improving the catalyst's cost-effectiveness. The excellent water adsorption and dissociation ability of transition metals contributes to the generation of a proton-rich local environment near the Pt-based alloy that promotes HER. Significant progress has been achieved in comprehending the alkaline HER mechanism through the manipulation of the structure and composition of electrocatalysts based on the Pt alloy. The objective of this review is to analyze and condense the latest developments in the production of Pt-based alloy electrocatalysts for alkaline HER. It focuses on the modified performance of Pt-based alloys and clarifies the design principles and catalytic mechanism of the catalysts from both an experimental and theoretical perspective. This review also highlights some of the difficulties encountered during the HER and the opportunities for increasing the HER performance. Finally, guidance for the development of more efficient Pt-based alloy electrocatalysts is provided.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Metastable Hexagonal-Phase Nickel with Ultralow Pt Content for an Efficient Alkaline/Seawater Hydrogen Evolution Reaction

Hydrogen has been hailed as the core of the world's future energy architecture. It is imperative to develop catalysts with an efficient and sustained hydrogen evolution reaction (HER) to scale up alkaline/seawater electrolysis, yet significant difficulties and challenges, such as the high usage of precious metals, still remain. In this paper, a metastable-phase hexagonal close-packed (hcp) Ni-based catalyst with ultralow Pt content (3.1 at %) was designed, which has excellent catalytic performance in the alkaline/seawater HER. The optimal catalyst offers low overpotentials of 21 and 137 mV at 10 mA cm-2 and remains stable during operation for 100 and 300 h at this current density in 1.0 M KOH and real seawater, respectively. A mechanistic study shows that the metastable-phase Ni acts as an anchor site for OH-, which promotes the dissociation of water and greatly improves the formation rate of H2.

Highly Dispersed Ni-Pt Bimetallic Cocatalyst: The Synergetic Effect Yields Pt-Like Activity in Photocatalytic Hydrogen Evolution

Achieving high photocatalytic activity with the lowest possible platinum (Pt) consumption is crucial for reducing the cost of Pt-based cocatalysts and enabling large-scale applications. Bimetallic Ni-Pt cocatalysts exhibit excellent photocatalytic performance and are considered one of the most promising photocatalysts capable of replacing pure Pt for hydrogen evolution reaction (HER). However, the synergistic photocatalytic mechanism between bimetallic Ni-Pt cocatalysts needs to be further investigated. Herein, we deposit highly dispersed Ni-Pt bimetallic cocatalysts on the surface of TiO2 by radiolytic reduction. We study the dynamics of photogenerated charge carriers of the Ni-Pt-comodified TiO2 and propose their underlying electron transfer mechanisms, in which Pt acts as an electron trap, whereas Ni serves as an electron supplier. The synergistic effect is Ni/Pt ratio-dependent and can confer bimetallic Ni-Pt to pure Pt-like photocatalytic activity in HER. The Ni2-Pt1-comodified TiO2 is optimized to be the most cost-effective photocatalyst with robust stability, which exhibits about 40-fold higher performance than bare TiO2.

Strain and Surface Engineering of Multicomponent Metallic Nanomaterials with Unconventional Phases

Multicomponent metallic nanomaterials with unconventional phases show great prospects in electrochemical energy storage and conversion, owing to unique crystal structures and abundant structural effects. In this review, we emphasize the progress in the strain and surface engineering of these novel nanomaterials. We start with a brief introduction of the structural configurations of these materials, based on the interaction types between the components. Next, the fundamentals of strain, strain effect in relevant metallic nanomaterials with unconventional phases, and their formation mechanisms are discussed. Then the progress in surface engineering of these multicomponent metallic nanomaterials is demonstrated from the aspects of morphology control, crystallinity control, surface modification, and surface reconstruction. Moreover, the applications of the strain- and surface-engineered unconventional nanomaterials mainly in electrocatalysis are also introduced, where in addition to the catalytic performance, the structure-performance correlations are highlighted. Finally, the challenges and opportunities in this promising field are prospected.

Design and Synthesis of Noble Metal-Based Alloy Electrocatalysts and Their Application in Hydrogen Evolution Reaction

Hydrogen energy is regarded as the ultimate energy source for future human society, and the preparation of hydrogen from water electrolysis is recognized as the most ideal way. One of the key factors to achieve large-scale hydrogen production by water splitting is the availability of highly active and stable electrocatalysts. Although non-precious metal electrocatalysts have made great strides in recent years, the best hydrogen evolution reaction (HER) electrocatalysts are still based on noble metals. Therefore, it is particularly important to improve the overall activity of the electrocatalysts while reducing the noble metals load. Alloying strategies can shoulder the burden of optimizing electrocatalysts cost and improving electrocatalysts performance. With this in mind, recent work on the application of noble metal-based alloy electrocatalysts in the field of hydrogen production from water electrolysis is summarized. In this review, first, the mechanism of HER is described; then, the current development of synthesis methods for alloy electrocatalysts is presented; finally, an example analysis of practical application studies on alloy electrocatalysts in hydrogen production is presented. In addition, at the end of this review, the prospects, opportunities, and challenges facing noble metal-based alloy electrocatalysts are tried to discuss.

Phase-Controlled Ruthenium Nanocrystals on Colloidal Polydopamine Supports and Their Catalytic Behaviors in Aerobic Oxidation Reactions

The past decade has witnessed rapidly growing interest in noble metal nanostructures adopting unconventional metastable crystal phases. In the case of Ru, chemically synthesized nanocrystals typically form thermodynamically favored hexagonal close-packed (hcp) crystal lattices, whereas it remains significantly more challenging to synthesize Ru nanocrystals in the metastable face-centered cubic (fcc) phase. In this work, we have synthesized polydopamine (PDA)-supported hcp and fcc Ru nanocrystals in a phase-selective manner through one-pot thermal reduction of appropriate Ru(III) precursors in a polyol solvent. Benefiting from the unique surface-adhesion function of PDA, we have been able to grow phase-controlled sub-5 nm Ru nanocrystals directly on colloidal PDA supports without prefunctionalizing the particle surfaces with any molecular linkers or surface-capping ligands. Success in phase-controlled synthesis of capping ligand-free Ru nanocrystals dispersed on the same support material enables us to systematically compare the intrinsic mass-specific and surface-specific activities of fcc and hcp Ru nanocatalysts toward the aerobic oxidation of a chromogenic molecular substrate, 3,3',5,5'-tetramethylbenzidine (TMB), under a broad range of reaction conditions. We use UV-vis absorption spectroscopy to monitor the conversion of the reactant molecules into the one-electron and two-electron oxidation products in real time during Ru-catalyzed oxidation of TMB, which is found to be a mechanistically complex molecule-transforming process involving multiple elementary steps. The apparent reaction rates and detailed kinetic features are observed to be not only intimately related to the crystalline structures of the Ru nanocatalysts but also profoundly influenced by several other critical factors, such as the pH of the reaction medium, the initial concentration of TMB, Ru coverage on the PDA supports, and degree of nanoparticle aggregation.

Highly Selective Synthesis of Monoclinic-Phased Platinum-Tellurium Nanotrepang for Direct Formic Acid Oxidation Catalysis

Designing efficient formic acid oxidation reaction (FAOR) catalysts with remarkable membrane electrode assembly (MEA) performance in a direct formic acid fuel cell (DFAFC) medium is significant yet challenging. Herein, we report that the monoclinic-phased platinum-tellurium nanotrepang (m-PtTe NT) can be adopted as a highly active, selective, and stable FAOR catalyst with a desirable direct reaction pathway. The m-PtTe NT exhibits the high specific and mass activities of 6.78 mA cm^-2 and 3.2 A mg_Pt^-1, respectively, which are 35.7/22.9, 2.8/2.6, and 3.9/2.9 times higher than those of commercial Pt/C, rhombohedral-phased Pt₂Te₃ NT (r-Pt₂Te₃ NT), and trigonal-phased PtTe₂ NT (t-PtTe₂ NT), respectively. Simultaneously, the highest reaction tendency for the direct FAOR pathway and the best tolerance to poisonous CO intermediate can also be realized by m-PtTe NT. More importantly, even in a single-cell medium, the m-PtTe NT can display a much higher MEA power density (171.4 mW cm^-2) and stability (53.2% voltage loss after 5660 s) than those of commercial Pt/C, demonstrating the great potential in operating DFAFC device. The in-situ Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy jointly demonstrate that the unique nanostructure of m-PtTe NT can effectively optimize dehydrogenation steps and inhibit the CO intermediate adsorption, as well as promote the oxidation of noxious CO intermediate, thus achieving the great improvement of FAOR activity, poisoning tolerance, and stability. Density functional theory calculations further reveal that the direct pathway is the most favorable on m-PtTe NT than r-Pt₂Te₃ NT and t-PtTe₂ NT. The higher activation energy to produce CO and the relatively weaker binding with CO of m-PtTe NT result in the better CO tolerance. This work achieves remarkable FAOR and MEA performances of advanced Pt-based anodic catalysts for DFAFCs via a phase engineering strategy.

Activating and optimizing the In-Plane interface of 1 T/2H MoS2 for efficient hydrogen evolution reaction

Implanting the octahedral phase (1 T) into the hexagonal phase (2H) of the molybdenum disulfide (MoS₂) matrix is considered one of the effective methods to enhance hydrogen evolution reaction (HER) performances of MoS₂. In this paper, hybrid 1 T/2H MoS₂ nanosheets array was successfully grown on conductive carbon cloth (1 T/2H MoS₂/CC) via facile hydrothermal method and the 1 T phase content in 1 T/2H MoS₂ is regulated to gradually increase from 0 % to 80 %. 1 T/2H MoS₂/CC with 75 % 1 T phase content exhibits optimal HER performances. The DFT calculation results show that S atoms in 1 T/2H MoS₂ interface exhibit the lowest hydrogen adsorption Gibbs free energies (ΔG_H*) compared with other sites. The improvement of HER performances are primarily attributed to activating the in-plane interface regions of the hybrid 1 T/2H MoS₂ nanosheets. Furthermore, the relationship between 1 T MoS₂ content in 1 T/2H MoS₂ and catalytic activity was simulated by a mathematical model, which shows that the catalytic activity presents a trend of increasing and then decreasing with the increase of 1 T phase content.

Coherent hexagonal platinum skin on nickel nanocrystals for enhanced hydrogen evolution activity

Metastable noble metal nanocrystals may exhibit distinctive catalytic properties to address the sluggish kinetics of many important processes, including the hydrogen evolution reaction under alkaline conditions for water-electrolysis hydrogen production. However, the exploration of metastable noble metal nanocrystals is still in its infancy and suffers from a lack of sufficient synthesis and electronic engineering strategies to fully stimulate their potential in catalysis. In this paper, we report a synthesis of metastable hexagonal Pt nanostructures by coherent growth on 3d transition metal nanocrystals such as Ni without involving galvanic replacement reaction, which expands the frontier of the phase-replication synthesis. Unlike noble metal substrates, the 3d transition metal substrate owns more crystal phases and lower cost and endows the hexagonal Pt skin with substantial compressive strains and programmable charge density, making the electronic properties particularly preferred for the alkaline hydrogen evolution reaction. The energy barriers are greatly reduced, pushing the activity to 133 mA cmgeo-2 and 17.4 mA μgPt-1 at -70 mV with 1.5 µg of Pt in 1 M KOH. Our strategy paves the way for metastable noble metal catalysts with tailored electronic properties for highly efficient and cost-effective energy conversion.

N-Doped Carbon Shells Encapsulated Ru-Ni Nanoalloys for Efficient Hydrogen Evolution Reaction

The alkaline hydrogen evolution reaction (HER) is of great significance for the large-scale green H₂ production. Currently, pressing challenges in the fabrication of cost-effective HER electrocatalysts are related to their sluggish water dissociation kinetics. Herein, a facile strategy to accelerate the desorption of HER intermediates and water dissociation is proposed. RuNi nanoalloy confined within N-doped carbon shells (Ru₇ Ni₃ @NC/C) with optimized Ru/Ni ratio and the dicyandiamide dosage was prepared. It displays an overpotential (η₁₀ ) of 16 mV, Tafel slope of 29.9 mV dec^-1 , and long-term stability over 10 000 cycles. The decent HER performance on Ru₇ Ni₃ @NC/C stems from the core-shell structure that is favoring the exposure of dispersed active sites, and the synergistic effect to promote water capture and dissociation. This work provides insight into the relationship between the HER performance and the electrochemical behavior of the intermediate adsorbed state, and paves an avenue toward rational design efficient electrocatalysts for HER.

High Chemical Potential Driven Amorphization of Pd-based Nanoalloys

Amorphous metals and alloys are promising candidates for superior catalysts in many catalytic and electrocatalytic reactions. It is of great urgency to develop a general method to construct amorphous alloys and further clarify the growth mechanism in a wet-chemical system. Herein, inspired by the conservation of energy during the crystallization process, amorphous PdCu nanoalloys have been successfully synthesized by promoting the chemical potential of the building blocks in solution. Benefiting from the abundant active sites and enhanced corrosion resistance, the synthesized amorphous PdCu nanostructures exhibit superior catalytic activity and durability over the face-centered cubic one in formic acid decomposition reaction. More importantly, the successful fabrications of amorphous PdFe, PdCo, and PdNi further demonstrate the universality of the above strategy. This proposed strategy is promising to diversify the amorphous family.

Pt-Quantum-Dot-Modified Sulfur-Doped NiFe Layered Double Hydroxide for High-Current-Density Alkaline Water Splitting at Industrial Temperature

Suitable electrocatalysts for industrial water splitting can veritably promote practical hydrogen applications. Rational surface design is exceptionally significant for electrocatalysts to bridge the gap between fundamental science and industrial expectation in water splitting. Here, Pt-quantum-dot-modified sulfur-doped NiFe layered double hydroxides (Pt@S-NiFe LDHs) are designed with eximious catalytic activity toward hydrogen evolution reaction (HER) under industrial condition. Benefiting from enhanced binding energy, mass transfer, and hydrogen release, Pt@S-NiFe LDHs exhibit outstanding activity in HER at high current densities. Notably, it obtains an impressively low overpotential of 71 mV and long-term stability of 200 h at 100 mA cm^-2 , exceeding commercial 40% Pt/C and most reported Pt-based electrocatalysts. Its mass activity is 2.7 times higher than that of 40% Pt/C with an overpotential of 100 mV. Furthermore, at industrial temperature (65 °C), the electrolyzer based on Pt@S-NiFe LDH needs just 1.62 V to reach the current density of 100 mA cm^-2 , superior to that of the commercial one of 40% Pt/C//IrO₂ . This work provides rational ideas to develop electrocatalysts with exceptional performance for industrial high-temperature water splitting at high current densities.

Alloying Pt into Ni partially amorphous for promoted alkaline hydrogen production

Aiming at the sluggish water dissociation step in alkaline hydrogen evolution reaction (HER), the platinum-nickel alloy material (PtNi₁₀/C) featuring unique crystalline/amorphous structure supported on carbon black is deliberately designed and fabricated via a reversely rapid co-precipitation and mild thermal reduction strategy. Electrochemical results show that only 66 mV of overpotential is needed for PtNi₁₀/C to drive a current density of 10 mA cm^-2 at a lower platinum loading (8.3 μg_Pt cm-2 geo), which is much lower than that of other catalysts with a single metal source(S-Ni/C and S-Pt/C) and even the commercial Pt/C catalyst (20 wt%). The target catalyst also exhibits smaller tafel slope value (16.73 mV dec^-1) and electrochemical impedance value, enabling a fast kinetics rate for water dissociation. Partial crystallization facilitates moderate adsorption of intermediates, while the high-valence Ni(II) and Pt(II) species serve as pivotal driving force for the kinetic dissociation of water. The unique microstructure of PtNi₁₀/C shows a remarkable advantage toward HER in alkaline but acidic medium. In addition, other transition metal-based catalysts following the similar protocol are also fabricated and present varying degrees of HER performance. Hence, the facile and rapid co-precipitation/thermal reduction strategy proposed in this study provides some guidelines for designing high-efficiency alkaline HER catalysts.

Dual Function of 4-Aminothiophene in Surface-Enhanced Raman Scattering Application as an Internal Standard and Adsorbent for Controlling Au Nanocrystal Morphology

The sensitivity and quantitative accuracy of surface-enhanced Raman scattering (SERS) are the main factors that restrict its application. Here, novel Au nanoscale convex polyhedrons (Au NCPs) were designed and fabricated to solve these problems via an embedded standard, including eight pods and six small protrusions. Spherical Au seeds regrew into different sizes of Au NCPs with a face-centered cubic structure. This morphology is due to the dual mechanism of the 4-aminothiophene (4-ATP) molecule that serves as an internal standard and a surface ligand regulator combined with the regulatory role of hexadecyl trimethyl ammonium chloride. The results show that Au NCPs were enclosed by high-index {12 9 1} facets, which greatly improved the local plasma resonance and reduced the lowest SERS detectable concentration of pyrene in standard seawater to 0.5 nM. An effective reference was produced by embedding 4-ATP with a relative standard deviation value less than 2.97% (in the same batch) and 3.92% (between different batches). Our research offers a new strategy for morphological regulation of metal nanocrystals, which is useful for the preparation of highly sensitive SERS substrates and trace analysis.

Revealing the Crystal Phase-Activity Relationship on NiRu Alloy Nanoparticles Encapsulated in N-Doped Carbon towards Efficient Hydrogen Evolution Reaction

Adjusting the crystal phase of a metal alloy is an important method to optimize catalytic performance. However, detailed understanding about the phase-property relationship for the hydrogen evolution reaction (HER) is still limited. In this work, the crystal phase-activity relationship of NiRu nanoparticles is studied employing N-doped carbon shell coated NiRu nanoparticles with different phase contents. It is found that the NiRu@NC (mix) with both face-centred cubic (fcc) and thermodynamically unstable hexagonal close-packed (hcp) phase NiRu give the best HER performance. Further activity studies demonstrate that hcp NiRu has better HER performance, and NiRu@NC (mix) with rich (∼70 %) hcp phase presented outstanding performance with an overpotential of only 27 mV @ 10 mA ⋅ cm^-2 . The high HER activity of NiRu@NC (mix) is attributed to the formation of hcp phase. This finding indicates that the regulation of crystal structure can provide a new strategy for optimizing HER activity.

Intermetallic Nanocrystal Discovery through Modulation of Atom Stacking Hierarchy

A library of compositionally and structurally well-defined Au-Cu alloy nanocrystals has been prepared via scanning probe block copolymer lithography. These libraries not only allow one to map compositional and structure space but also the conditions (e.g., cooling rate) required to access specific structures. This approach enabled the realization of a previously unobserved architecture, an intermetallic nanoprism, that is a consequence of hierarchical atom stacking. These structures exhibit distinctive diffraction patterns characterized by non-integer-index, forbidden spots, which serve as a diagnostic indicator of such structures. Inspection of the library's pseudospherical particles reveals a high-strain cubic-tetragonal interfacial configuration in the outer regions of the intermetallic nanocrystals. Since it is costly and time-consuming to explore the nanomaterials phase space via conventional wet-chemistry, this parallel kinetic-control approach, which relies on substrate- and positionally isolated particles, may lead to the rapid discovery of complex nanocrystals that may prove useful in applications spanning catalysis and plasmonic sensing.

FeCoNi Ternary Nano-Alloys Embedded in a Nitrogen-Doped Porous Carbon Matrix with Enhanced Electrocatalysis for Stable Lithium-Sulfur Batteries

The application of composite materials that combine the advantages of carbonaceous material and metal alloy proves to be a valid method for improving the performance of lithium-sulfur batteries (LSBs). Herein iron-cobalt-nickel (FeCoNi) ternary alloy nanoparticles (FNC) that spread on nitrogen-doped carbon (NC) are obtained by a strategy of low-temperature sol-gel followed by annealing at 800 °C under an argon/hydrogen atmosphere. Benefiting from the synergistic effect of different components of FNC and the conductive network provided by the NC, not only can the "shuttle effect" of lithium polysulfides (LiPS) be suppressed, but also the conversion of LiPS, the diffusion of Li⁺, and the deposition of Li₂S can be accelerated. Taking advantage of those merits, the batteries assembled with an FNC@NC-modified polypropylene (PP) separator (FNC@NC//PP) can deliver a high reversible specific capacity of 1325 mAh g^-1 at 0.2 C and maintain 950 mAh g^-1 after 200 cycles, and they can also achieve a low capacity fading rate of 0.06% per cycle over 500 cycles at 1 C. More impressively, even under harsh test conditions (the ratio of electrolyte to sulfur (E/S) = 6 μL mg^-1 and sulfur loading = 4.7 mg cm^-2 and E/S = 10 μL mg^-1 and sulfur loading = 5.9 mg cm^-2), the area capacity of batteries is still much higher than 4 mAh cm^-2.

Recent Development of Nickel-Based Electrocatalysts for Urea Electrolysis in Alkaline Solution

Recently, urea electrolysis has been regarded as an up-and-coming pathway for the sustainability of hydrogen fuel production according to its far lower theoretical and thermodynamic electrolytic cell potential (0.37 V) compared to water electrolysis (1.23 V) and rectification of urea-rich wastewater pollution. The new era of the "hydrogen energy economy" involving urea electrolysis can efficiently promote the development of a low-carbon future. In recent decades, numerous inexpensive and fruitful nickel-based materials (metallic Ni, Ni-alloys, oxides/hydroxides, chalcogenides, nitrides and phosphides) have been explored as potential energy saving monofunctional and bifunctional electrocatalysts for urea electrolysis in alkaline solution. In this review, we start with a discussion about the basics and fundamentals of urea electrolysis, including the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER), and then discuss the strategies for designing electrocatalysts for the UOR, HER and both reactions (bifunctional). Next, the catalytic performance, mechanisms and factors including morphology, composition and electrode/electrolyte kinetics for the ameliorated and diminished activity of the various aforementioned nickel-based electrocatalysts for urea electrolysis, including monofunctional (UOR or HER) and bifunctional (UOR and HER) types, are summarized. Lastly, the features of persisting challenges, future prospects and expectations of unravelling the bifunctional electrocatalysts for urea-based energy conversion technologies, including urea electrolysis, urea fuel cells and photoelectrochemical urea splitting, are illuminated.

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.

Anion-Exchange Membrane Water Electrolyzers

This Review provides an overview of the emerging concepts of catalysts, membranes, and membrane electrode assemblies (MEAs) for water electrolyzers with anion-exchange membranes (AEMs), also known as zero-gap alkaline water electrolyzers. Much of the recent progress is due to improvements in materials chemistry, MEA designs, and optimized operation conditions. Research on anion-exchange polymers (AEPs) has focused on the cationic head/backbone/side-chain structures and key properties such as ionic conductivity and alkaline stability. Several approaches, such as cross-linking, microphase, and organic/inorganic composites, have been proposed to improve the anion-exchange performance and the chemical and mechanical stability of AEMs. Numerous AEMs now exceed values of 0.1 S/cm (at 60-80 °C), although the stability specifically at temperatures exceeding 60 °C needs further enhancement. The oxygen evolution reaction (OER) is still a limiting factor. An analysis of thin-layer OER data suggests that NiFe-type catalysts have the highest activity. There is debate on the active-site mechanism of the NiFe catalysts, and their long-term stability needs to be understood. Addition of Co to NiFe increases the conductivity of these catalysts. The same analysis for the hydrogen evolution reaction (HER) shows carbon-supported Pt to be dominating, although PtNi alloys and clusters of Ni(OH)2 on Pt show competitive activities. Recent advances in forming and embedding well-dispersed Ru nanoparticles on functionalized high-surface-area carbon supports show promising HER activities. However, the stability of these catalysts under actual AEMWE operating conditions needs to be proven. The field is advancing rapidly but could benefit through the adaptation of new in situ techniques, standardized evaluation protocols for AEMWE conditions, and innovative catalyst-structure designs. Nevertheless, single AEM water electrolyzer cells have been operated for several thousand hours at temperatures and current densities as high as 60 °C and 1 A/cm2, respectively.

Morphology-Tuned Pt3 Ge Accelerates Water Dissociation to Industrial-Standard Hydrogen Production over a wide pH Range

The discovery of novel materials for industrial-standard hydrogen production is the present need considering the global energy infrastructure. A novel electrocatalyst, Pt₃ Ge, which is engineered with a desired crystallographic facet (202), accelerates hydrogen production by water electrolysis, and records industrially desired operational stability compared to the commercial catalyst platinum is introduced. Pt₃ Ge-(202) exhibits low overpotential of 21.7 mV (24.6 mV for Pt/C) and 92 mV for 10 and 200 mA cm^-2 current density, respectively in 0.5 m H₂ SO₄ . It also exhibits remarkable stability of 15 000 accelerated degradation tests cycles (5000 for Pt/C) and exceptional durability of 500 h (@10 mA cm^-2 ) in acidic media. Pt₃ Ge-(202) also displays low overpotential of 96 mV for 10 mA cm^-2 current density in the alkaline medium, rationalizing its hydrogen production ability over a wide pH range required commercial operations. Long-term durability (>75 h in alkaline media) with the industrial level current density (>500 mA cm^-2 ) has been demonstrated by utilizing the electrochemical flow reactor. The driving force behind this stupendous performance of Pt₃ Ge-(202) has been envisaged by mapping the reaction mechanism, active sites, and charge-transfer kinetics via controlled electrochemical experiments, ex situ X-ray photoelectron spectroscopy, in situ infrared spectroscopy, and in situ X-ray absorption spectroscopy further corroborated by first principles calculations.

Fabrication and Characterization of Nanostructured Rock Wool as a Novel Material for Efficient Water-Splitting Application

Rock wool (RW) nanostructures of various sizes and morphologies were prepared using a combination of ball-mill and hydrothermal techniques, followed by an annealing process. Different tools were used to explore the morphologies, structures, chemical compositions and optical characteristics of the samples. The effect of initial particle size on the characteristics and photoelectrochemical performance of RW samples generated hydrothermally was investigated. As the starting particle size of ball-milled natural RW rises, the crystallite size of hydrothermally formed samples drops from 70.1 to 31.7 nm. Starting with larger ball-milled particle sizes, the nanoparticles consolidate and seamlessly combine to form a continuous surface with scattered spherical nanopores. Water splitting was used to generate photoelectrochemical hydrogen using the samples as photocatalysts. The number of hydrogen moles and conversion efficiencies were determined using amperometry and voltammetry experiments. When the monochromatic wavelength of light was increased from 307 to 460 nm for the manufactured RW>0.3 photocatalyst, the photocurrent density values decreased from 0.25 to 0.20 mA/mg. At 307 nm and +1 V, the value of the incoming photon-to-current efficiency was ~9.77%. Due to the stimulation of the H+ ion rate under the temperature impact, the Jph value increased by a factor of 5 when the temperature rose from 40 to 75 °C. As a result of this research, for the first time, a low-cost photoelectrochemical catalytic material is highlighted for effective hydrogen production from water splitting.

Insight into the effects of the crystal phase of Ru over ultrathin Ru@Pt core-shell nanosheets for methanol electrooxidation

Coating a second metal on the surface of ultrathin 2D nanosheets (NSs) could induce lattice strain and modify the electronic structure, thereby changing the surface reactivity. Herein, we report the effects of different crystal phases of Ru on the electrocatalytic performance of ultrathin Ru@Pt core-shell NSs for the methanol oxidation reaction (MOR). Importantly, Ru with a novel face-centered-cubic phase was found to have more effect on the electronic structure of Pt than Ru with a conventional hexagonal close-packed phase, thereby leading to improved electrocatalytic activity toward the MOR under acidic and basic conditions. It is believed that the strategy presented here would offer a new approach to the construction of bimetallic core-shell nanostructures with various promising applications.

Concave Pt-Zn Nanocubes with High-Index Faceted Pt Skin as Highly Efficient Oxygen Reduction Catalyst

High dosage of expensive Pt to catalyze the sluggish oxygen reduction reaction (ORR) on the cathode severely impedes the commercialization of proton exchange membrane fuel cells. Therefore, it is urgent to cut down the Pt catalyst by efficiently improving the ORR activity while maintaining high durability. Herein, magic concave Pt-Zn nanocubes with high-index faceted Pt skin (Pt78 Zn22 ) are proposed for high-efficiency catalysis toward proton exchange membrane fuel cells. These unique structural features endow the Pt-skin Pt78 Zn22 /KB with a mass activity of 1.18 mA μgPt -1 and a specific activity of 3.64 mA cm-2 for the ORR at 0.9 V (vs RHE). Meanwhile, the H2 -O2 fuel cell assembled by this catalyst delivers an ultrahigh peak power density of ≈1449 mW cm-2 . Both experiments and theoretical calculations show that the electronic structure of the surface is adjusted, thereby shortening the length of the Pt-Pt bond and reducing the adsorption energy of OH*/O* on the Pt surface. This work demonstrates the synergistic effect of the oxidation-resistant metal Zn and the construction of Pt-rich surface engineering. Also, it guides the future development of catalysts for their practical applications in energy conversion technologies and beyond.

Hydrogen spillover in complex oxide multifunctional sites improves acidic hydrogen evolution electrocatalysis

Improving the catalytic efficiency of platinum for the hydrogen evolution reaction is valuable for water splitting technologies. Hydrogen spillover has emerged as a new strategy in designing binary-component Pt/support electrocatalysts. However, such binary catalysts often suffer from a long reaction pathway, undesirable interfacial barrier, and complicated synthetic processes. Here we report a single-phase complex oxide La₂Sr₂PtO_7+δ as a high-performance hydrogen evolution electrocatalyst in acidic media utilizing an atomic-scale hydrogen spillover effect between multifunctional catalytic sites. With insights from comprehensive experiments and theoretical calculations, the overall hydrogen evolution pathway proceeds along three steps: fast proton adsorption on O site, facile hydrogen migration from O site to Pt site via thermoneutral La-Pt bridge site serving as the mediator, and favorable H₂ desorption on Pt site. Benefiting from this catalytic process, the resulting La₂Sr₂PtO_7+δ exhibits a low overpotential of 13 mV at 10 mA cm⁻², a small Tafel slope of 22 mV dec⁻¹, an enhanced intrinsic activity, and a greater durability than commercial Pt black catalyst.

While renewable H₂ production offers a promising route for clean energy production, there is an urgent need to improve catalyst performances. Here, authors design a Pt-containing complex oxide that utilizes atomic-scale hydrogen spillover to promote H₂ evolution electrocatalysis in acidic media.