Metallic nanostructures with low dimensionality for electrochemical water splitting

2D PtRhPb Mesoporous Nanosheets with Surface-Clean Active Sites for Complete Ethanol Oxidation Electrocatalysis

The development of active and selective metal electrocatalysts for complete ethanol oxidation reaction (EOR) into desired C1 products is extremely promising for practical application of direct ethanol fuel cells. Despite some encouraging achievements, their activity and selectivity remain unsatisfactory. In this work, it is reported that 2D PtRhPb mesoporous nanosheets (MNSs) with anisotropic structure and surface-clean metal site perform perfectly for complete EOR electrocatalysis in both three-electrode and two-electrode systems. Different to the traditional routes, a selective etching strategy is developed to produce surface-clean mesopores while retaining parent anisotropy quasi-single-crystalline structure without the mesopore-forming surfactants. This method also allows the general synthesis of surface-clean mesoporous metals with other compositions and structures. When being performed for alkaline EOR electrocatalysis, the best PtRhPb MNSs deliver remarkably high activity (7.8 A mg-1) and superior C1 product selectivity (70% of Faradaic efficiency), both of which are much better than reported electrocatalysts. High performance is assigned to multiple structural and compositional synergies that not only stabilized key OHads intermediate by surface-clean mesopores but also separated the chemisorption of two carbons in ethanol by adjacent Pt and Rh sites, which facilitate the oxidation cleavage of stable C─C bond for complete EOR electrocatalysis.

Recent Developments in Nickel-Based Layered Double Hydroxides for Photo(-/)electrocatalytic Water Oxidation

Layered double hydroxides (LDHs), especially those containing nickel (Ni), are increasingly recognized for their potential in photo(-/)electrocatalytic water oxidation due to the abundant availability of Ni, their corrosion resistance, and their minimal toxicity. This review provides a comprehensive examination of Ni-based LDHs in electrocatalytic (EC), photocatalytic (PC), and photoelectrocatalytic (PEC) water oxidation processes. The review delves into the operational principles, highlighting similarities and distinctions as well as the benefits and limitations associated with each method of water oxidation. It includes a detailed discussion on the synthesis of monolayer, ultrathin, and bulk Ni-based LDHs, focusing on the merits and drawbacks inherent to each synthesis approach. Regarding the EC oxygen evolution reaction (OER), strategies to improve catalytic performance and insights into the structural evolution of Ni-based LDHs during the electrocatalytic process are summarized. Furthermore, the review extensively covers the advancements in Ni-based LDHs for PEC OER, including an analysis of semiconductors paired with Ni-based LDHs to form photoanodes, with a focus on their enhanced activity, stability, and underlying mechanisms facilitated by LDHs. The review concludes by addressing the challenges and prospects in the development of innovative Ni-based LDH catalysts for practical applications. The comprehensive insights provided in this paper will not only stimulate further research but also engage the scientific community, thus driving the field of photo(-/)electrocatalytic water oxidation forward.

Rational Construction of 3D Self-Supported MOF-Derived Cobalt Phosphide-Based Hollow Nanowall Arrays for Efficient Overall Water Splitting At large Current Density

Developing efficient nonprecious bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) in the same electrolyte with a low overpotential and large current density presents an appealing yet challenging goal for large-scale water electrolysis. Herein, a unique 3D self-branched hierarchical nanostructure composed of ultra-small cobalt phosphide (CoP) nanoparticles embedded into N, P-codoped carbon nanotubes knitted hollow nanowall arrays (CoPʘNPCNTs HNWAs) on carbon textiles (CTs) through a carbonization-phosphatization process is presented. Benefiting from the uniform protrusion distributions of CoP nanoparticles, the optimum CoPʘNPCNTs HNWAs composites with high abundant porosity exhibit superior electrocatalytic activity and excellent stability for OER in alkaline conditions, as well as for HER in both acidic and alkaline electrolytes, even under large current densities. Furthermore, the assembled CoPʘNPCNTs/CTs||CoPʘNPCNTs/CTs electrolyzer demonstrates exceptional performance, requiring an ultralow cell voltage of 1.50 V to deliver the current density of 10 mA cm-2 for overall water splitting (OWS) with favorable stability, even achieving a large current density of 200 mA cm-2 at a low cell voltage of 1.78 V. Density functional theory (DFT) calculation further reveals that all the C atoms between N and P atoms in CoPʘNPCNTs/CTs act as the most efficient active sites, significantly enhancing the electrocatalytic properties. This strategy, utilizing 2D MOF arrays as a structural and compositional material to create multifunctional composites/hybrids, opens new avenues for the exploration of highly efficient and robust non-noble-metal catalysts for energy-conversion reactions.

Flexible Hydrazone-Linked Metal-Covalent Organic Frameworks with Copper Clusters for Efficient Electrocatalytic Oxygen Evolution Reaction

Despite the challenges associated with the synthesis of flexible metal-covalent organic frameworks (MCOFs), these offer the unique advantage of maximizing the atomic utilization efficiency. However, the construction of flexible MCOFs with flexible building units or linkages has rarely been reported. In this study, novel flexible MCOFs are constructed using flexible building blocks and copper clusters with hydrazone linkages. The heterometallic frameworks (Cu, Co) are prepared through the hydrazone linkage coordination method and evaluated as catalysts for the oxygen evolution reaction (OER). Owing to the spatial separation and functional cooperation of the heterometallic MCOF catalysts, the as-synthesized MCOFs exhibited outstanding catalytic activities with an overpotential of 268.8 mV at 10 mA cm-2 for the OER in 1 M KOH, which is superior to those of the reported covalent organic frameworks (COFs)-based OER catalysts. Theoretical calculations further elucidated the synergistic effect of heterometallic active sites within the linkages and frameworks, contributing to the enhanced OER activity. This study thus introduces a novel approach to the fundamental design of flexible MCOF catalysts for the OER, emphasizing their enhanced atomic utilization efficiency.

Enhancing the electronic structure of Ni-based electrocatalysts through N element substitution for the hydrogen evolution reaction

The weak orbital coupling between Ni3N and H2O, caused by its interstitial structure and attenuated Ni-N interaction, is attributed to the high unoccupied d orbital energy of Ni3N. Consequently, the kinetics for water dissociation in the HER are slow. In this study, we effectively lowered the energy state of vacant d orbitals in Ni3N, which resulted in an exceptionally efficient HER. The as-synthesized Ni3N catalyst demonstrates an overpotential of 135 mV when subjected to a current density of 10 mA cm-2. The refined structural characterization suggests that the introduction of oxygen results in a reduction in electron densities surrounding the Ni sites. Furthermore, DFT calculations provide additional evidence that the electrocatalyst of Ni3N generates a greater number of lowest unoccupied orbitals (LUMOs) and improved alignment, thereby enhancing the adsorption and splitting of water. The notion of orbital-regulated electronic levels on Ni sites introduces a distinctive methodology for the systematic development of catalysts used in hydrogen evolution and other applications.

First-row transition metal carbonates catalyze the electrochemical oxygen evolution reaction: iron is master of them all

In pursuing green hydrogen fuel, electrochemical water-splitting emerges as the optimal method. A critical challenge in advancing this process is identifying a cost-effective electrocatalyst for oxygen evolution on the anode. Recent research has demonstrated the efficacy of first-row transition metal carbonates as catalysts for various oxidation reactions. In this study, Earth-abundant first-row transition metal carbonates were electrodeposited onto nickel foam (NF) electrodes and evaluated for their performance in the oxygen evolution reaction. The investigation compares the activity of these carbonates on NF electrodes against bare NF electrodes. Notably, Fe2(CO3)3/NF exhibited superior oxygen evolution activity, characterized by low overpotential values, i.e. Iron is master of them all (R. Kipling, Cold Iron, Rewards and Fairies, Macmillan and Co. Ltd., 1910). Comprehensive catalytic stability and durability tests also indicate that these transition metal carbonates maintain stable activity, positioning them as durable and efficient electrocatalysts for the oxygen evolution reaction.

Electronic redistribution through the interface of MnCo2O4-Ni3N nano-urchins prompts rapid In situ phase transformation for enhanced oxygen evolution reaction

One of the most coveted objectives in the realm of energy conversion technologies is the development of highly efficient and economically viable electrocatalysts for the oxygen evolution reaction. The commercialization of such techniques has thus far been impeded by their slow response kinetics. One of the many ways to develop highly effective electrocatalysts is to judiciously choose a coupling interface that maximizes catalyst performance. In this study, the in situ electrochemical phase transformation of MnCo2O4-Ni3N into MnCo2O4-NiOOH is described. The catalyst has an exceptional overpotential of 224 mV to drive a current density of 10 mA cm-2. Strong interfacial contact is seen in the MnCo2O4-Ni3N catalyst, leading to a considerable electronic redistribution between the MnCo2O4 and Ni3N phases. This causes an increase in the valence state of Ni, which makes it an active site for the adsorption of *OH, O*, and *OOH (intermediates). This charge transfer facilitates the rapid phase transformation to form NiOOH from Ni3N. At a higher current density of 300 mA cm-2, the catalyst remained stable for a period of 140 h. DFT studies also revealed that the in situ-formed NiOOH on the MnCo2O4 surface results in superior OER kinetics compared to that of NiOOH alone.

Ru Single Atoms Integrated into Cobalt Oxide Spinel Structure with Interstitial Carbon for Enhanced Electrocatalytic Water Oxidation

Oxygen evolution reaction (OER) plays a critical role in energy conversion technologies. Significant progress has been made in alkaline conditions. In contrast, it remains a challenge to develop stable OER electrocatalysts in acidic conditions. Herein, a new strategy is reported to stabilize single atoms integrated into cobalt oxide spinel structure with interstitial carbon (Ru0.27Co2.73O4), where the optimized Ru0.27Co2.73O4 exhibits a low overpotential of 265, 326, and 367 mV to reach a current density of 10, 50, and 100 mA cm2, respectively. More importantly, Ru0.27Co2.73O4 has long-term stability of up to 100 h, representing one of the most stable OER electrocatalysts. X-ray adsorption spectroscopy (XAS) characterization and density functional theory (DFT) calculations jointly demonstrate that the significant catalytic performance of Ru0.27Co2.73O4 is due to the synergistic effect between the Ru and Co sites and the bridging O ligands, as well as the significant reduction of the OER energy barrier. This work provides a new perspective for designing and constructing efficient non-noble metal-based electrocatalysts for water splitting.

Reversing the Interfacial Electric Field in Metal Phosphide Heterojunction by Fe-Doping for Large-Current Oxygen Evolution Reaction

Developing non-precious-metal electrocatalysts that can operate with a low overpotential at a high current density for industrial application is challenging. Heterogeneous bimetallic phosphides have attracted much interest. Despite high hydrogen evolution reaction (HER) performance, the ordinary oxygen evolution reaction (OER) performance hinders their practical use. Herein, it is shown that Fe-doping reverses and enlarges the interfacial electrical field at the heterojunction, turning the H intermediate favorable binding sites for HER into O intermediate favorable sites for OER. Specifically, the self-supported heterojunction catalysts on nickel foam (CoP@Ni2P/NF and Fe-CoP@Fe-Ni2P/NF) are readily synthesized. They only require the overpotentials of 266 and 274 mV to drive a large current density of 1000 mA cm-2 (j1000) for HER and OER, respectively. Furthermore, a water splitting cell equipped with these electrodes only requires a voltage of 1.724 V to drive j1000 with excellent durability, demonstrating the potential of industrial application. This work offers new insights on interfacial engineering for heterojunction catalysts.

Catalysis with Two-Dimensional Metal-Organic Frameworks: Synthesis, Characterization, and Modulation

The demand for the exploration of highly active and durable electro/photocatalysts for renewable energy conversion has experienced a significant surge in recent years. Metal-organic frameworks (MOFs), by virtue of their high porosity, large surface area, and modifiable metal centers and ligands, have gained tremendous attention and demonstrated promising prospects in electro/photocatalytic energy conversion. However, the small pore sizes and limited active sites of 3D bulk MOFs hinder their wide applications. Developing 2D MOFs with tailored thickness and large aspect ratio has emerged as an effective approach to meet these challenges, offering a high density of exposed active sites, better mechanical stability, better assembly flexibility, and shorter charge and photoexcited state transfer distances compared to 3D bulk MOFs. In this review, synthesis methods for the most up-to-date 2D MOFs are first overviewed, highlighting their respective advantages and disadvantages. Subsequently, a systematic analysis is conducted on the identification and electronic structure modulation of catalytic active sites in 2D MOFs and their applications in renewable energy conversion, including electrocatalysis and photocatalysis (electro/photocatalysis). Lastly, the current challenges and future development of 2D MOFs toward highly efficient and practical electro/photocatalysis are proposed.

Strain Effects in Ru-Au Bimetallic Aerogels Boost Electrocatalytic Hydrogen Evolution

To improve the sluggish kinetics of the hydrogen evolution reaction (HER), a key component in water-splitting applications, there is an urgent desire to develop efficient, cost-effective, and stable electrocatalysts. Strain engineering is proving an efficient strategy for increasing the catalytic activity of electrocatalysts. This work presents the development of Ru-Au bimetallic aerogels by a simple one-step in situ reduction-gelation approach, which exhibits strain effects and electron transfer to create a remarkable HER activity and stability in an alkaline environment. The surface strain induced by the bimetallic segregated structure shifts the d-band center downward, enhancing catalysis by balancing the processes of water dissociation, OH* adsorption, and H* adsorption. Specifically, the optimized catalyst shows low overpotentials of only 24.1 mV at a current density of 10 mA cm-2 in alkaline electrolytes, surpassing commercial Pt/C. This study can contribute to the understanding of strain engineering in bimetallic electrocatalysts for HER at the atomic scale.

Ruthenium-Based Binary Alloy with Oxide Nanosheath for Highly Efficient and Stable Oxygen Evolution Reaction in Acidic Media

Traditional noble metal oxide, such as RuO2, is considered a benchmark catalyst for acidic oxygen evolution reaction (OER). However, its practical application is limited due to sluggish activity and severe electrochemical corrosion. In this study, Ru-Fe nanoparticles loading on carbon felt (RuFe@CF) is synthesized via an ultrafast Joule heating method as an active and durable OER catalyst in acidic conditions. Remarkably low overpotentials of 188 and 269 mV are achieved at 10 and 100 mA cm-2, respectively, with a robust stability up to 620 h at 10 mA cm-2. When used as an anode in a proton exchange membrane water electrolyzer, the catalyst shows more than 250 h of stability at a water-splitting current of 200 mA cm-2. Experimental characterizations reveal the presence of a Ru-based oxide nanosheath on the surface of the catalyst during OER tests, suggesting a surface reconstruction process that enhances the intrinsic activity and inhibits continuous metal dissolution. Moreover, density functional theory calculations demonstrate that the introduction of Fe into the RuFe@CF catalyst reduces the energy barrier and boosts its activities. This work offers an effective and universal strategy for the development of highly efficient and stable catalysts for acidic water splitting.

Research progress on layered metal oxide electrocatalysts for an efficient oxygen evolution reaction

Hydrogen, highly valued for its pristine cleanliness and remarkable efficiency as an emerging energy source, is anticipated to ascend to a preeminent status within the forthcoming energy landscape. Electrocatalytic water splitting is considered a pivotal, eco-friendly, and sustainable strategy for hydrogen production. The substantial energy consumption stemming from oxygen evolution side reactions significantly impedes the commercial viability of water electrolysis. Consequently, the pursuit of a cost-effective and efficacious oxygen evolution reaction (OER) catalyst stands as an imperative strategy for realizing hydrogen production via water electrolysis. Layered metal oxides, owing to their robust anisotropic properties, versatile adjustability, and extensive surface area, have emerged as suitable candidates for OER catalysts. However, owing to the distinctive attributes of layered metal oxides, ongoing investigations into these materials are slightly fragmented, lacking universal consensus. This article comprehensively surveys the recent advancements in layered metal oxide-based OER catalysts, categorized into single metal oxides, alkali cobalt oxides, perovskites, and miscellaneous metal oxides. Initially, the main OER intermediate reaction steps of layered metal oxides are scrutinized. Subsequently, the design, mechanism, and application of several pivotal layered metal oxides in the OER are systematically delineated. Finally, a summary is provided, alongside the proposal of future research trajectories and challenges encountered by layered metal oxides, with the aspiration that this paper may serve as a valuable reference for scholars in the field.

Synthesis and Catalytic Performance of Mo2C/MoS2 Composite Heterojunction Catalysts

Hydrogen, as a clean, safe, and efficient energy carrier, is one of the hot energy sources that have attracted much attention. Mo2C, due to the introduction of C atoms, makes the atomic spacing of the Mo lattice decrease and changes the width of the d-band, which makes the electronic properties of Mo2C similar to that of Pt noble metals, exhibiting excellent electrochemical hydrogen precipitation performance. MoS2, due to its special crystal structure and tunable electronic structure, has been widely studied. In this paper, Mo2C nanoparticles were prepared by high-temperature carbonization, and then two-dimensional layered MoS2 were be loaded on Mo2C nanoparticles by the hydrothermal method to synthesize Mo2C/MoS2 composite catalysts. Their electrochemical hydrogen precipitation (HER) performance under acidic conditions was tested. The above catalysts were also characterized by modern material testing methods such as XRD, SEM, TEM, and XPS. The results showed that the composite catalysts exhibited the most excellent electrochemical hydrogen precipitation performance at Mo2C/MoS2-3, with the lowest overpotential at a current density of 10 mA cm-2, Tafel slope, and electrochemical impedance. At the same time, the electrochemically active area was dramatically enhanced, with good stability under prolonged testing. The catalytic activity was significantly improved compared with that of Mo2C and MoS2. The characterization and experimental results indicate that the heterogeneous structure of Mo2C and MoS2 formed a built-in electric field between the two, which accelerated the electron transfer efficiency and provided more active sites. The Mo2C/MoS2 composite catalyst is a low-cost, easy-to-prepare, and high-efficiency electrochemical hydrogen precipitation catalyst, providing a new idea for developing green and clean energy.

Ultrafine CoRu alloy nanoclusters densely anchored on Nitrogen-Doped graphene nanotubes for a highly efficient hydrogen evolution reaction

Designing highly efficient and stable electrocatalysts for hydrogen evolution reactions (HER) is essential to the production of green and renewable hydrogen. Metal-organic framework (MOF) precursor strategies are promising for the design of excellent electrocatalysts because of their porous architectures and adjustable compositions. In this study, a hydrogen-bonded organic framework (HOF) nanowire was developed as a precursor and template for the controllable and scalable synthesis of CoRu-MOF nanotubes. After calcination in Ar, the CoRu-MOF nanotubes were converted into N-doped graphene (NG) nanotubes with ultrafine CoRu nanoclusters (hereon called Co-xRu@NG-T; x  = 0, 5, 10, 15, 25 representing the Ru content of 0-0.25 mmol; T = 400 °C to 700 °C) that were densely encapsulated and isolated on the shell. Taking advantage of the synergistic effects of the porous, one-dimensional hollow structure and ultrafine CoRu nanoclusters, the optimized Co-15Ru@NG-500 catalyst demonstrated superior catalytic performance for HERs in alkaline electrolytes with an overpotential of only 30 mV at 10 mA cm-2 and robust durability for 2000 cycles, which outperforms many typical catalytic materials, such as commercial Pt/C. This work introduces a novel high-efficiency and cost-effective HER catalyst for application in commercial water-splitting electrolysis.

Effect of multi-interface electron transfer on water splitting and an innovative electrolytic cell for synergistic hydrogen production and degradation

The cleaning and utilization of industry wastewater are still a big challenge. In this work, we mainly investigate the effect of electron transfer among multi-interfaces on water electrolysis reaction. Typically, the CoS2, Co3S4/CoS2 (designated as CS4-2) and Co3S4/Co9S8/CoS2 (designated as CS4-8-2) samples are prepared on a large scale by one-step molten salt method. It is found that because of the different work functions (designated as WF; WF(Co3S4) = 4.48eV, WF(CoS2) = 4.41eV, WF(Co9S8) = 4.18 eV), the effective heterojunctions at the multi-interfaces of CS4-8-2 sample, which obviously improve interface charge transfer. Thus, the CS4-8-2 sample shows an excellent oxygen evolution reaction (OER) activity (134 mV/10 mA cm-2, 40 mV dec-1). The larger double-layer capacitance (Cdl = 17.1 mF cm-2) of the CS4-8-2 sample indicates more electrochemical active sites, compared to the CoS2 and CS4-2 samples. Density functional theory (DFT) calculation proves that due to interface polarization under electric field, the multi-interfaces effectively promote electron transfer and regulate electron structure, thus promoting the adsorption of OH- and dissociation of H2O. Moreover, an innovative norfloxacin (NFX) electrolytic cell (EC) is developed through introducing NFX into the electrolyte, in which efficient NFX degradation and hydrogen production are synergistically achieved. To reach 50 mA cm-2, the required cell voltage of NFX-EC has decreased by 35.2%, compared to conventional KOH-EC. After 2h running at 1 V, 25.5% NFX was degraded in the NFX EC. This innovative NFX-EC is highly energy-efficient, which is promising for the synergistic cleaning and utilization of industry wastewater.

Electrochemical Generation of Te Vacancy Pairs in PtTe for Efficient Hydrogen Evolution

Two-dimensional (2D) van der Waals materials are increasingly seen as potential catalysts due to their unique structures and unmatched properties. However, achieving precise synthesis of these remarkable materials and regulating their atomic and electronic structures at the most fundamental level to enhance their catalytic performance remain a significant challenge. In this study, we synthesized single-crystal bulk PtTe crystals via chemical vapor transport and subsequently produced atomically thin, large PtTe nanosheets (NSs) through electrochemical cathode intercalation. These NSs are characterized by a significant presence of Te vacancy pairs, leading to undercoordinated Pt atoms on their basal planes. Experimental and theoretical studies together reveal that Te vacancy pairs effectively optimize and enhance the electronic properties (such as charge distribution, density of states near the Fermi level, and d-band center) of the resultant undercoordinated Pt atoms. This optimization results in a significantly higher percentage of dangling O-H water, a decreased energy barrier for water dissociation, and an increased binding affinity of these Pt atoms to active hydrogen intermediates. Consequently, PtTe NSs featuring exposed and undercoordinated Pt atoms demonstrate outstanding electrocatalytic activity in hydrogen evolution reactions, significantly surpassing the performance of standard commercial Pt/C catalysts.

MOF-based/derived catalysts for electrochemical overall water splitting

Water-splitting electrocatalysis has gained increasing attention as a promising strategy for developing renewable energy in recent years, but its high overpotential caused by the unfavorable thermodynamics has limited its widespread implementation. Therefore, there is an urgent need to design catalytic materials with outstanding activity and stability that can overcome the high overpotential and thus improve the electrocatalytic efficiency. Metal-organic frameworks (MOFs) based and/or derived materials are widely used as water-splitting catalysts because of their easily controlled structures, abundant heterointerfaces and increased specific surface area. Herein, some recent research findings on MOFs-based/derived materials are summarized and presented. First, the mechanism and evaluation parameters of electrochemical water splitting are described. Subsequently, advanced modulation strategies for designing MOFs-based/derived catalysts and their catalytic performance toward water splitting are summarized. In particular, the correlation between chemical composition/structural functionalization and catalytic performance is highlighted. Finally, the future outlook and challenges for MOFs materials are also addressed.

FeNiCo|MnGaOx Heterostructure Nanoparticles as Bifunctional Electrocatalyst for Zn-Air Batteries

Driven by the pressing demand for stable energy systems, zinc-air batteries (ZABs) have emerged as crucial energy storage solutions. However, the quest for cost-effective catalysts to enhance vital oxygen evolution and reduction reactions remains challenging. FeNiCo|MnGaOx heterostructure nanoparticles on carbon nanotubes (CNTs) are synthesized using liquid-phase reduction and H2 calcination approach. Compared to its component, such FeNiCo|MnGaOx/CNT shows a high synergistic effect, low impedance, and modulated electronic structure, leading to a superior bifunctional catalytic performance with an overpotential of 255 mV at 10 mA cm-2 and half-wave potential of 0.824 V (ω = 1600 rpm and 0.1 m KOH electrolyte). Moreover, ZABs based on FeNiCo|MnGaOx/CNT demonstrate notable features, including a peak power density of 136.1 mW cm-2, a high specific capacity of 808.3 mAh gZn -1, and outstanding stability throughout >158 h of uninterrupted charge-discharge cycling. Theoretical calculations reveal that the non-homogeneous interface can introduce more carriers and altered electronic structures to refine intermediate adsorption reactions, especially promoting O* formation, thereby enhancing electrocatalytic performance. This work demonstrates the importance of heterostructure interfacial modulation of electronic structure and enhancement of adsorption capacity in promoting the implementation of OER/ORR, ZABs, and related applications.

Interfacial Electron Potential Well Facilitates the Design of Cobalt Phosphide Heterojunctions for Hydrogen Evolution

The interfacial electron modulation of electrocatalysts is an effective way to realize efficient hydrogen production, which is of great importance for future renewable energy systems. However, systematic theory-guided design of catalysts in heterojunction coupling is lacking. In this work, a multi-level theoretical calculation is performed to screen optimal candidates to form a heterojunction with CoP (101) surface for electrocatalytic hydrogen production. To overcome the weak adsorption of H+ on CoP (101), rational design of electrons potential well at the heterojunction interface can effectively enhance the hydrogen adsorption. All p-type cobalt-based phosphides are considered potential candidates at the beginning. After screening for conductivity, stability, interface matching screening, and ΔGH* evaluation, the CoP/Co2P-H system is identified to be able to display optimal hydrogen production performance. To verify the theoretical design, CoP, CoP/Co2P-H, and CoP/Co2P-O are synthesized and the electrochemical analysis is carried out. The hydrogen evolution reaction (HER) performance is consistent with the prediction. This work utilizes the electron potential well effect and multi-level screening calculations to design highly efficient heterojunction catalysts, which can provide useful theoretical guidance for the rational design of heterojunction-type catalysts.

Atom-by-atom optimizing the surface termination of Fe-Pt intermetallic catalysts for alkaline hydrogen evolution reaction

Controlling the atomic arrangement of elemental atoms in intermetallic catalysts to govern their surface and subsurface properties is a crucial but challenging endeavor in electrocatalytic reactions. In hydrogen evolution reaction (HER), adjusting the d-band center of the conventional noble-metallic Pt by introducing Fe enables the optimization of catalytic performance. However, a notable gap exists in research on the effective transition from disordered Fe/Pt alloys to highly ordered intermetallic compounds (IMCs) such as FePt3 in the alkaline HER, hampering their broader application. In this study, a series of catalysts FePt3-xH (x = 5, 6, 7, 8 and 9) supported on carbon nanotubes (CNTs) were synthesized via a simple impregnation method, along with a range of heat treatment processes, including annealing in a reductive atmosphere, to regulate the order degree of the arrangement of Fe/Pt atoms within the FePt3 catalyst. By using advanced microscopy and spectroscopy techniques, we systematically explored the impact of the order degree of FePt3 in the HER. The as-prepared FePt3-8H exhibited notable HER catalytic activity with low overpotentials (η = 37 mV in 1.0 mol L-1 KOH) at j = 10 mA cm-2. The surface of the L12 FePt3-8H catalyst was demonstrated to be Pt-rich. The Pt on the surface was not easily oxidized due to the unique Fe/Pt coordination, resulting in significant enhancement of HER performance.

Enhanced Alkaline Hydrogen Evolution Reaction via Electronic Structure Regulation: Activating PtRh with Rare Earth Tm Alloying

Developing high-performance electrocatalysts for alkaline hydrogen evolution reaction (HER) is crucial for producing green hydrogen, yet it remains challenging due to the sluggish kinetics in alkaline environments. Pt is located near the peak of HER volcano plot, owing to its exceptional performance in hydrogen adsorption and desorption, and Rh plays an important role in H2O dissociation. Lanthanides (Ln) are commonly used to modulate the electronic structure of materials and further influence the adsorption/desorption of reactants, intermediates, and products, and noble metal-Ln alloys are recognized as effective platforms where Ln elements regulate the catalytic properties of noble metals. Here Pt1.5Rh1.5Tm alloy is synthesized using the sodium vapor reduction method. This alloy demonstrates superior catalytic activity, being 4.4 and 6.6 times more effective than Pt/C and Rh/C, respectively. Density Functional Theory (DFT) calculations reveal that the upshift of d-band center and the charge transfer induced by alloying promote adsorption and dissociation of H2O, making Pt1.5Rh1.5Tm alloy more favorable for the alkaline HER reaction, both kinetically and thermodynamically.

Ni and Co Active Site Transition and Competition in Fluorine-Doped NiCo(OH)2 LDH Electrocatalysts for Oxygen Evolution Reaction

The oxygen evolution reaction (OER) performance of NiCo LDH electrocatalysts can be improved through fluorine doping. The roles of Ni and Co active sites in such catalysts remain ambiguous and controversial. In addressing the issue, this study draws upon the molecular orbital theory and proposes the active center competitive mechanism between Ni and Co. The doped F-atoms can directly impact the valence state of metal atoms or exert an indirect influence through the dehydrogenation, thereby modulating the active center. As the F-atoms are progressively aggregate, the eg orbitals of Ni and Co transition from e2 g to e1 g , and subsequently to e0 g . The corresponding valence state elevates from +2 to +3, and then to +4, signifying an initial increase followed by a subsequent decrease in the electrocatalytic performance. Furthermore, a series of F-NiCo LDH catalysts are synthesized to verify the eg orbital occupancy analysis, and the catalytic OER overpotentials are 303, 243, 240, and 246 mV at the current density of 10 mA cm-2 , respectively, which coincides well with the theoretical prediction. This investigation not only provides novel mechanistic insights into the transition and competition of Ni and Co in F-NiCo LDH catalysts but also establishes a foundation for the design of high-performance catalysts.

Acidic Oxygen Evolution Reaction: Fundamental Understanding and Electrocatalysts Design

Water electrolysis driven by "green electricity" is an ideal technology to realize energy conversion and store renewable energy into hydrogen. With the development of proton exchange membrane (PEM), water electrolysis in acidic media suitable for many situations with an outstanding advantage of high gas purity has attracted significant attention. Compared with hydrogen evolution reaction (HER) in water electrolysis, oxygen evolution reaction (OER) is a kinetic sluggish process that needs a higher overpotential. Especially in acidic media, OER process poses higher requirements for the electrocatalysts, such as high efficiency, high stability and low costs. This review focuses on the acidic OER electrocatalysis, reaction mechanisms, and critical parameters used to evaluate performance. Especially the modification strategies applied in the design and construction of new-type electrocatalysts are also summarized. The characteristics of traditional noble metal-based electrocatalysts and the noble metal-free electrocatalysts developed in recent decades are compared and discussed. Finally, the current challenges for the most promising acidic OER electrocatalysts are presented, together with a perspective for future water electrolysis.

Emerging two dimensional metastable-phase oxides: insights and prospects in synthesis and catalysis

Since the discovery of graphene, the development of new two-dimensional (2D) materials has received considerable interest. Recently, as a newly emerging member of the 2D family, 2D metastable-phase oxides that combine the unique advantages of metal oxides, 2D structures, and metastable-phase materials have shown enormous potential in various catalytic reactions. In this review, the potential of various 2D materials to form a metastable-phase is predicted. The advantages of 2D metastable-phase oxides for advanced applications, reliable methods of synthesizing 2D metastable-phase oxides, and the application of these oxides in different catalytic reactions are presented. Finally, the challenges associated with 2D metastable-phase oxides and future perspectives are discussed.

Optimizing Intermediate Adsorption on Pt Sites via Triple-Phase Interface Electronic Exchange for Methanol Oxidation

For the most commonly applied platinum-based catalysts of direct methanol fuel cells, the adsorption ability toward reaction intermediates, including CO and OH, plays a vital role in their catalytic activity and antipoisoning in anodic methanol oxidation reaction (MOR). Herein, guided by a theoretical mechanism study, a favorable modulation of the electronic structure and intermediate adsorption energetics for Pt active sites is achieved by constructing the triple-phase interfacial structure between tin oxide (SnO2), platinum (Pt), and nitrogen-doped graphene (NG). From the strong electronic exchange at the triple-phase interface, the adsorption ability toward MOR reaction intermediates on Pt sites could be efficiently optimized, which not only inhibits the adsorption of CO* on active sites but also facilitates the adsorption of OH* to strip the poisoning species from the catalyst surface. Accordingly, the resulting catalyst delivers excellent catalytic activity and antipoisoning ability for MOR catalysis. The mass activity reaches 1098 mA mg-1Pt, 3.23 times of commercial Pt/C. Meanwhile, the initial potentials and main peak for CO oxidation are also located at a much lower potential (0.51 and 0.74 V) against commercial Pt/C (0.83 and 0.89 V).

Enhanced Alkaline Hydrogen Evolution Reaction through Lanthanide-Modified Rhodium Intermetallic Catalysts

Design of highly efficient electrocatalysts for alkaline hydrogen evolution reaction (HER) is of paramount importance for water electrolysis, but still a considerable challenge because of the slow HER kinetics in alkaline environments. Alloying is recognized as an effective strategy to enhance the catalytic properties. Lanthanides (Ln) are recognized as an electronic and structural regulator, attributed to their unique 4f electron behavior and the phenomenon known as lanthanide contraction. Here, a new class of Rh3Ln intermetallics (IMs) are synthesized using the sodium vapor reduction method. The alloying process induced an upshift of the d-band center and electron transfer from Ln to Rh, resulting in optimized adsorption and dissociation energies for H2O molecules. Consequently, Rh3Tb IMs exhibited outstanding HER activity in both alkaline environments and seawater, displaying an overpotential of only 19 mV at 10 mA cm-2 and a Tafel slope of 22.2 mV dec-1. Remarkably, the current density of Rh3Tb IMs at 100 mV overpotential is 8.6 and 5.7 times higher than that of Rh/C and commercial Pt/C, respectively. This work introduces a novel approach to the rational design of HER electrocatalysis and sheds light on the role of lanthanides in electrocatalyst systems.

Robust Ru-VO2 Bifunctional Catalysts for All-pH Overall Water Splitting

Designing robust bifunctional catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction in all-pH conditions for overall water splitting (OWS) is an effective way to achieve sustainable development. Herein, a composite Ru-VO2 containing Ru-doped VO2 and Ru nanoparticles (NPs) is synthesized, and it shows a high OWS performance in full-pH range due to their synergist effect. In particular, the OER mass activities of Ru-VO2 at 1.53 V (vs RHE) in acidic, alkaline, and PBS solutions are ≈65, 36, and 235 times of commercial RuO2 in the same conditions. The "Ru-VO2 || Ru-VO2 " two-electrode electrolyzer only needs a voltage of 1.515 V (at 10 mA cm-2 ) in acidic water splitting, which can operate stably for 125 h at 10 mA cm-2 without significant voltage decay. In situ Raman spectra and in situ differential electrochemical mass spectrometry prove that the OER of Ru-VO2 in acid follows the adsorption evolution mechanism. Density functional theory calculations further reveal the synergistic effect between Ru NP and Ru-doped VO2 , which breaks the hydrogen bond network formed by *OH adsorbed on the Ru single-atom site, and thereby significantly enhances the OER activity. This work provides new insights into the design of novel bifunctional pH-universal catalysts for OWS.

Interfacial π-p Electron Coupling Prompts Hydrogen Evolution Reaction Activity in Acidic Electrolyte

The thermodynamically stable 2H-phase MoS2 is a brilliant material toward hydrogen evolution reaction (HER) owing to its excellent Gibbs free energy of hydrogen adsorption. Nevertheless, the poor intrinsic properties of 2H-MoS2 limit its electrocatalytic performances toward HER. In this work, graphitic carbon nitride covalently bridging 2H-MoS2 (MoS2/GCN) is proposed to construct robust HER electrocatalysts. The strong π-p electron coupling between the delocalized π electrons of GCN and the localized p electrons of S atoms sufficiently expose active sites and accelerate the reaction kinetics. To be specific, MoS2/GCN exhibits remarkable HER activity (160 mV at 10 mA·cm-2) and long-term durability. Importantly, MoS2/GCN also provides great potential for industrial application. Density functional theory (DFT) calculations disclose that the π-p electron coupling at the MoS2/GCN interface regulates the electronic structure of S atoms, consequently providing enhanced HER performance. This work presents a feasible pathway to develop advanced electrocatalysts for energy conversions.

Understanding the improvement mechanism of plasma etching treatment on oxygen reduction reaction catalysts

Plasma etching treatment is an effective strategy to improve the electrocatalytic activity, but the improvement mechanism is still unclear. In this work, a nitrogen-doped carbon nanotube-encased iron nanoparticles (Fe@NCNT) catalyst is synthesized as the model catalyst, followed by plasma etching treatment with different parameters. The electrocatalytic activity improvement mechanism of the plasma etching treatment is revealed by combining the physicochemical characterizations and electrochemical results. As a result, highly active metal-nitrogen species introduced by nitrogen plasma etching treatment are recognized as the main contribution to the improved electrocatalytic activity, and the defects induced by plasma etching treatment also contribute to the improvement of the electrocatalytic activity. In addition, the prepared catalyst also demonstrates superior ORR activity and stability than the commercial Pt/C catalyst.

Electronic configuration regulation of single-atomic Mn sites mediated by Mo/Mn clusters for an efficient hydrogen evolution reaction

Tuning the electron distribution of metal single-atom active sites via bimetallic clusters is an effective way to enhance their hydrogen evolution reaction (HER) activity, but remains a great challenge. A biochar-based electrocatalyst (BCMoMn800-2) with both MnN4 active sites and Mo2C/Mn7C3 clusters was synthesized using in situ enriched Mo/Mn biomass as a precursor to trigger the HER. Various characterization and density functional theory (DFT) calculation results indicated that the presence of Mo2C/Mn7C3 clusters in BCMoMn800-2 effectively induced the redistribution of charges at MnN4 sites, reducing the energy of H* activation during the HER. In 0.5 M H2SO4, the overpotential was 27.4 mV at a current density of 10 mA cm-2 and the Tafel slope was 31 mV dec-1, and its electrocatalytic performance was close to that of Pt/C. The electrocatalyst also exhibited excellent electrocatalytic stability and durability. This work might provide a new strategy for solid waste recycling and constructing efficient HER electrocatalysts.

Interface Engineering with the Coupling of a 3D Porous Structure Enables MoP2-NiCoP Heterostructure Nanosheets for Enhanced Alkaline Hydrogen Evolution Reaction

One of the crucial parts of the electrochemically focused energy conversion and storage system is the hydrogen evolution reaction. The further exploration of electrocatalysts made of nonprecious metals could help to bring the technology closer to industrialization. Here, we present an effective hydrogen evolution reaction (HER) electrocatalyst that employs hydrothermal and phosphorization steps to create three-dimensional (3D) porous MoP2-NiCoP heterostructure nanosheets on nickel foam (MoP2-NiCoP/NF). H2O-dissociation and H-adsorption were effectively achieved due to the distinctive interface engineering between NiCoP and MoP2, which functions as a channel for immediate electron transfer. Compared to the single-component MoP2 and NiCoP, the synergistic interaction between the heterogeneous components coupling and the 3D porous structure enables MoP2-NiCoP/NF to exhibit satisfactory catalytic activity with an ultralow overpotential of 50 mV at 10 mA cm-2, which is close to the commercial Pt/C catalyst in alkaline media. More importantly, it exhibits good stability, with the ability to be electrolyzed in 1.0 M KOH electrolyte for 24 h without a significant change in overpotential. This study offers directions for the design of low-cost, high-activity, transition metal phosphides (TMPs)-based HER catalyst alternatives for future practical applications.

Amorphous Nickel Hydroxide Shell on Ni8P3 Nanorods for Boosted Highly Stable Overall Water Splitting at High Current

Developing highly active, highly stable, and cheap electrocatalysts for water splitting is of great significance for hydrogen production. Herein, we report an amorphous Ni(OH)2-clothed transition Ni8P3 catalyst, in which the amorphous Ni(OH)2 shell provides catalytic active sites and serves as a proton conductive encapsulation layer to ensure efficient proton supply to the active Ni8P3 sites. As expected, the Ni8P3@Ni(OH)2 catalyst exhibits significant water decomposition performance at low and high current densities of 10, 100, and 1000 mA cm-2 at 1.45, 1.71, and 2.21 V, respectively, which is comparable to those of commercial electrocatalysts. In particular, the prepared Ni8P3@Ni(OH)2 electrodes possess exceptional long-term durability (200 h) at high current (over 1 A). The significantly improved water-splitting activity and durability in alkaline medium are expected to make them attractive catalyst materials to produce renewable chemical fuels.

Controllable Electrochemical Liberation of Hydrogen from Sodium Borohydride

Sodium borohydride (NaBH4 ) has earned recognition as a promising hydrogen carrier, attributed to its exceptional hydrogen storage capacity, boasting a high theoretical storage capacity of 10.8 wt %. Nonetheless, the utilization of traditional pyrolysis and hydrolysis methods still presents a formidable challenge in achieving controlled hydrogen generation especially under ambient conditions. In this work, we report an innovative electrochemical strategy for production H2 by coupling NaBH4 electrooxidation reaction (BOR) at anode in alkaline media with hydrogen evolution reaction (HER) at cathode in acidic media. To implement this, we have developed a bifunctional electrocatalyst denoted as Pd-Mo2 C@CNTs, wherein Pd nanoparticles are grown in situ on Mo2 C embedded within N-doped carbon nanotubes. This electrocatalyst demonstrates exceptional performance in catalyzing both alkaline BOR and acidic HER. We have developed a hybrid acid/alkali cell, utilizing Pd/Mo2 C@CNTs as the anode and cathode electrocatalysts. This configuration showcases remarkable capabilities for self-sustained, precise, and uninterrupted indirect release of H2 stored in NaBH4 , even at high current densities of 100 mA cm-2 with a Faraday efficiency approaching 100 %. Additionally, this electrochemical device exhibits significant promise as a fuel cell, with the ability to deliver a maximum power density of 20 mW cm-2 .

Surface defect-engineered Fe doping in layered Co-based complex as highly efficient bifunctional electrocatalysts for overall water splitting

The electrocatalytic splitting of water to produce hydrogen is regarded as an efficient and promising strategy but is limited by its large overpotential; thus, a highly efficient electrocatalyst is urgently needed. Mixed metal doping is an important strategy in defect engineering because the heteroatoms can change the intrinsic structure to form defects by affecting the atomic coordination mode and adjusting the electronic structure, which is often accompanied by morphological changes. Herein, two-dimensional layered bimetallic Co-pydc containing axially coordinated water molecules was selected by producing surface defects through Fe doping in Co centers as bifunctional electrocatalysts for OER and HER. The optimized Co0.59Fe0.41-pydc possesses outstanding OER performance with the lowest overpotential of 262 mV to reach j = 10 mA cm-2, and Co0.75Fe0.25-pydc possesses superior HER performance with the lowest overpotential of 96 mV at j = 10 mA cm-2. Furthermore, the overall water splitting device assembled with Co0.59Fe0.41-pydc@NF//Co0.59Fe0.41-pydc@NF affords a current density of 10 mA cm-2 at only 1.687 V. This work emphasizes the surface defects formed by tuning the electronic structure of metal centres accompanied with morphological changes of bimetallic dopants for efficient overall water splitting.

Construction of bimetallic phosphide nanostructures with in situ growth, reduction, and phosphidation of ultra-thin graphene layers as highly efficient catalysts towards the OER

We present a novel approach for the in situ growth of bimetallic silicate onto ultrathin graphene, followed by in situ reduction and phosphorization to obtain uniformly dispersed bimetallic phosphides (rGO@FeNiP/rGO@FeCoP) on graphene layers. Unlike the traditional simple composites of single-metallic phosphides and carbon materials, the bimetallic synergy of rGO@FeNiP/rGO@FeCoP obtained through in situ growth, reduction, phosphorization, and alkaline treatment exhibits a large surface area, more nanopores and defects, and more active sites, facilitates electrolyte diffusion and gas release, accelerates electron transfer and enhances electrocatalytic oxygen evolution reaction (OER) performance. Furthermore, the continuous carbon layer architecture surrounding FeNiP/FeCoP provides structural support, improving catalyst stability. We have investigated the effect of different proportions of bimetals on electrocatalytic performance, providing a rational design and synthesis strategy for carbon-based bimetallic phosphides as a promising electrocatalyst for the OER.

N-Coordinated Iridium-Molybdenum Dual-Atom Catalysts Enabling Efficient Bifunctional Hydrogen Electrocatalysis

Achieving effective hydrogen evolution/oxidation reaction (HER/HOR) across a wide pH span is of critical importance in unlocking the full potential of hydrogen energy but remains intrinsically challenging. Here, we engineer the N-coordinated Ir-Mo dual atoms on a carbon matrix by ultrafast high-temperature sintering, creating an efficient bifunctional electrocatalyst for both HER and HOR in both acidic and alkaline electrolytes. The optimized catalyst, Ir-Mo DAC/NC, demonstrates exceptional performance, with a significantly reduced HER overpotential of 11.3 mV at 10 mA/cm2 and a HOR exchange current (i0,m) of 3972 mA/mgIr in acidic conditions, surpassing the performance of Pt/C and Ir/C catalysts. In alkaline conditions, Ir-Mo DAC/NC also outperforms Pt/C, as evidenced by its low HER overpotential of 23 mV at 10 mA/cm2 and a high i0,m of 1308 mA/mgIr. Furthermore, our catalyst exhibits remarkable stability in both acidic and alkaline environments. DFT calculations results reveal that the superior electrochemical performance of Ir-Mo DAC/NC arises from the electronic synergy between Ir and Mo pairs, which regulates the interaction between the intermediates and active sites. These findings present a promising strategy for the development of dual-atom catalysts (DACs), with potential applications in the polymer fuel cells and water electrolyzers.

Metal nitrides for seawater electrolysis

Electrocatalytic high-throughput seawater electrolysis for hydrogen production is a promising green energy technology that offers possibilities for environmental and energy sustainability. However, large-scale application is limited by the complex composition of seawater, high concentration of Cl- leading to competing reaction, and severe corrosion of electrode materials. In recent years, extensive research has been conducted to address these challenges. Metal nitrides (MNs) with excellent chemical stability and catalytic properties have emerged as ideal electrocatalyst candidates. This review presents the electrode reactions and basic parameters of the seawater splitting process, and summarizes the types and selection principles of conductive substrates with critical analysis of the design principles for seawater electrocatalysts. The focus is on discussing the properties, synthesis, and design strategies of MN-based electrocatalysts. Finally, we provide an outlook for the future development of MNs in the high-throughput seawater electrolysis field and highlight key issues that require further research and optimization.

Hollow Spherical Heterostructured FeCo-P Catalysts Derived from MOF-74 for Efficient Overall Water Splitting

The design of catalysts with tunable active sites in heterogeneous interface structures is crucial for addressing challenges in the water-splitting process. Herein, a hollow spherical heterostructure FeCo-P is successfully prepared by hydrothermal and phosphorization methods. This hollow structure, along with the heterogeneous interface between Co2 P and FeP, not only facilitates the exposure of more active sites, but also increases the contact area between the catalyst and the electrolyte, as well as shortens the distance for mass/electron transfer. This enhancement promotes electron transfer to facilitate water decomposition. FeCo-P exhibits excellent hydrogen evolution (HER) and oxygen evolution (OER) performance when reaching @ 10 mA cm-2 in 1 mol L-1  KOH, with overpotentials of 131/240 mV for HER/OER. Furthermore, when FeCo-P is used as both the cathode and anode for overall water splitting (OWS), it only requires low voltages of 1.49, 1.55, and 1.57 V to achieve CDs of 10, 100, and 300 mA cm-2 , respectively. Density functional theory calculations indicate that constructing a Co2 P and FeP heterogeneous interface with good lattice matching can facilitate electron redistribution, thereby enhancing the electrocatalytic performance of OWS. This work opens up new possibilities for the rational design of efficient water electrolysis catalysts derived from MOFs.

Interfacial Electron Regulation and Composition Evolution of NiFe/MoC Heteronanowire Arrays for Highly Stable Alkaline Seawater Oxidation

In alkaline seawater electrolysis, the oxygen evolution reaction (OER) is greatly suppressed by the occurrence of electrode corrosion due to the formation of hypochlorite. Herein, a catalyst consisting of MoC nanowires modified with NiFe alloy nanoparticles (NiFe/MoC) on nickel foam (NF) is prepared. The optimized catalyst can deliver a large current density of 500 mA cm-2 at a very low overpotential of 366 mV in alkaline seawater, respectively, outperforming commercial IrO2 . Remarkably, an electrolyzer assembled with NiFe/MoC/NF as the anode and NiMoN/NF as the cathode only requires 1.77 V to drive a current density of 500 mA cm-2 for alkaline seawater electrolysis, as well as excellent stability. Theory calculation indicates that the initial activity of NiFe/MoC is attributed to increased electrical conductivity and decreased energy barrier for OER due to the introduction of Fe. We find that the change of the catalyst in the composition occurred after the stability test; however, the reconstructed catalyst has an energy barrier close to that of the pristine one, which is responsible for its excellent long-term stability. Our findings provide an efficient way to construct high-performance OER catalysts for alkaline seawater splitting.

Cobalt vacancy-originated TiMnCoCN compounds with a self-adjusting ability for the high-efficiency acidic oxygen evolution reaction

Oxygen evolution reaction (OER) electrocatalysts in acidic media, except for precious IrO2, have difficulty realizing good electrocatalytic activity and high electrochemical stability simultaneously. However, the scarcity of IrO2 as an acidic OER electrocatalyst impedes its large-scale application in hydrogen generation, organic synthesis, nonferrous metal production and sewage disposal. Herein, we report the design and fabrication of a nanoporous TiMnCoCN compound based on the nanoscale Kirkendall effect, possessing an intriguing self-adjusting capability for the oxygen evolution reaction (OER) in a 0.5 M H2SO4 solution. The nanoporous TiMnCoCN compound electrode for the acidic OER displays a low overpotential of 143 mV for 10 mA cm-2 and exhibits no increase in potential over 50,000 s, which is ascribed to the self-adjusting ability, Carbon/nitrogen (C/N) incorporation and nanoporous architecture. The concentration of inert TiO2 on the reconstructed surface of the compound can self-adjust with the change in OER potential via a cobalt-dissolved vacancy approach according to the stabilization requirement. In this work, the self-reconstruction law of surface structure was discovered, providing a novel strategy for designing and fabricating nonnoble OER electrocatalysts with superior catalytic performance and robust stability in acidic media.

Two-dimensional mesoporous metals: a new era for designing functional electrocatalysts

Two-dimensional (2D) mesoporous metals contribute a unique class of electrocatalyst materials for electrochemical applications. The penetrated mesopores of 2D mesoporous metals expose abundant accessible undercoordinated metal sites, while their 2D nanostructures accelerate the transport of electrons and reactants. Therefore, 2D mesoporous metals have exhibited add-in structural functions with great potential in electrocatalysis that not only enhance electrocatalytic activity and stability but also optimize electrocatalytic selectivity. In this Perspective, we summarize recent progress in the design, synthesis, and electrocatalytic performance of 2D mesoporous metals. Four main strategies for synthesizing 2D mesoporous metals, named the CO (and CO container) induced route, halide ion-oriented route, interfacial growth route, and metal oxide atomic reconstruction route, are presented in detail. Moreover, electrocatalytic applications in several important reactions are summarized to highlight the add-in structural functions of 2D mesoporous metals in enhancing electrochemical activity, stability, and selectivity. Finally, current challenges and future directions are discussed in this area. This Perspective offers some important insights into both fundamental investigations and practical applications of novel high-performance functional electrocatalysts.

Ternary Rare Earth Alloy Pt3-xIrxSc Nanoparticles Modulate Negatively Charged Pt via Charge Transfer To Facilitate pH-Universal Hydrogen Evolution

Rare earth (RE) elements possess electronic configurations that can provide additional pathways for tailoring the electronic structures of active elements through alloying, making it an important area of exploration in electrocatalysis. However, the large negative redox potential between RE and Pt has hindered the development of RE nanoalloys. In this study, a solid-phase synthesis strategy was employed to synthesize ternary Pt3-xIrxSc nanoparticles (NPs). By leveraging the electronegativity difference between Pt (2.28), Ir (2.20), and Sc (1.36), a charge-balance strategy was implemented to stabilize and enhance the catalytic performance of the alloy. The electron transfer from Sc to Pt/Ir results in the latter being negatively charged, and the Ir modifies the electron density of Pt, enabling favorable adsorption of active H species during the hydrogen evolution reaction (HER). Pt2IrSc exhibits enhanced HER activity at all pH values, achieving low overpotentials at 10 mA cm-2 of only 13, 18, and 25 mV in 0.5 M H2SO4, 1 M PBS, and 1 M KOH, respectively. This electrocatalyst also exhibits robust electrocatalytic stability even after 20,000 cycles. This work represents an application of the charge balance strategy to RE nanoalloys, and it is expected to inspire the design and synthesis of highly reactive RE nanoalloys.

High-entropy alloys in electrocatalysis: from fundamentals to applications

High-entropy alloys (HEAs) comprising five or more elements in near-equiatomic proportions have attracted ever increasing attention for their distinctive properties, such as exceptional strength, corrosion resistance, high hardness, and excellent ductility. The presence of multiple adjacent elements in HEAs provides unique opportunities for novel and adaptable active sites. By carefully selecting the element configuration and composition, these active sites can be optimized for specific purposes. Recently, HEAs have been shown to exhibit remarkable performance in electrocatalytic reactions. Further activity improvement of HEAs is necessary to determine their active sites, investigate the interactions between constituent elements, and understand the reaction mechanisms. Accordingly, a comprehensive review is imperative to capture the advancements in this burgeoning field. In this review, we provide a detailed account of the recent advances in synthetic methods, design principles, and characterization technologies for HEA-based electrocatalysts. Moreover, we discuss the diverse applications of HEAs in electrocatalytic energy conversion reactions, including the hydrogen evolution reaction, hydrogen oxidation reaction, oxygen reduction reaction, oxygen evolution reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, and alcohol oxidation reaction. By comprehensively covering these topics, we aim to elucidate the intricacies of active sites, constituent element interactions, and reaction mechanisms associated with HEAs. Finally, we underscore the imminent challenges and emphasize the significance of both experimental and theoretical perspectives, as well as the potential applications of HEAs in catalysis. We anticipate that this review will encourage further exploration and development of HEAs in electrochemistry-related applications.

Deformable Catalytic Material Derived from Mechanical Flexibility for Hydrogen Evolution Reaction

Deformable catalytic material with excellent flexible structure is a new type of catalyst that has been applied in various chemical reactions, especially electrocatalytic hydrogen evolution reaction (HER). In recent years, deformable catalysts for HER have made great progress and would become a research hotspot. The catalytic activities of deformable catalysts could be adjustable by the strain engineering and surface reconfiguration. The surface curvature of flexible catalytic materials is closely related to the electrocatalytic HER properties. Here, firstly, we systematically summarized self-adaptive catalytic performance of deformable catalysts and various micro-nanostructures evolution in catalytic HER process. Secondly, a series of strategies to design highly active catalysts based on the mechanical flexibility of low-dimensional nanomaterials were summarized. Last but not least, we presented the challenges and prospects of the study of flexible and deformable micro-nanostructures of electrocatalysts, which would further deepen the understanding of catalytic mechanisms of deformable HER catalyst.

Ultrathin RhCo alloy nanowires with defect-rich active sites for alkaline hydrogen evolution electrocatalysis

One-dimensional RhCo alloy nanowires (NWs) with an ultrathin thickness (2.6 nm) and abundant defect sites were prepared in an aqueous solution by a nanoconfined attachment growth route within assembled columnar micelles. Thanks to dual synergies between advantageous anisotropic ultrathin structures and alloy compositions, they endowed one-dimensional RhCo NWs with superior activity and high stability for alkaline hydrogen evolution electrocatalysis.

Amorphous-crystalline heterostructures enable energy-level matching of cobalt sulfide/nickel iron layered double hydroxide for efficient oxygen evolution reaction

Interface engineering of heterostructures has emerged as a promising approach to enhance the catalytic activity of nonprecious electrocatalysts. Herein, a novel amorphous cobalt sulfide-crystalline nickel iron layered double hydroxide (a-CoS@NiFe-LDH) hybrid material is presented for application as an electrocatalyst for oxygen evolution reaction (OER). Benefitting from the well-matched energy level structures, the a-CoS@NiFe-LDH catalyst delivers a low overpotential of 221 ± 14 mV at an OER current density of 20 mA cm-2 and a small Tafel slope of 83.1 mV dec-1, showing good OER properties. First-principle computations reveal that the electronic interaction between amorphous cobalt sulfide (a-CoS) and crystalline nickel iron layered double hydroxide (NiFe-LDH) components within a-CoS@NiFe-LDH promotes the adsorbate evolution mechanism and reduces the adsorption energies for oxygen intermediates, thereby enhancing the activity and stability for OER. This work opens up a new avenue to enhance the OER catalytic efficiency via the construction of amorphous-crystalline heterostructures.

Bubble Engineering on Micro-/Nanostructured Electrodes for Water Splitting

Bubble behaviors play crucial roles in mass transfer and energy efficiency in gas evolution reactions. Combining multiscale structures and surface chemical compositions, micro-/nanostructured electrodes have drawn increasing attention. With the aim to identify the exciting opportunities and rationalize the electrode designs, in this review, we present our current comprehension of bubble engineering on micro-/nanostructured electrodes, focusing on water splitting. We first provide a brief introduction of gas wettability on micro-/nanostructured electrodes. Then we discuss the advantages of micro-/nanostructured electrodes for mass transfer (detailing the lowered overpotential, promoted supply of electrolyte, and faster bubble growth kinetics), localized electric field intensity, and electrode stability. Following that, we outline strategies for promoting bubble detachment and directional transportation. Finally, we offer our perspectives on this emerging field for future research directions.

One-pot synthesis of 3D surface-wrinkled PdAu nanospheres for robust alcohols electrocatalysis

Three dimensional (3D) noble-metal nanomaterials with special surface structures have been regarded as high-performance catalysts for alcohol oxidation on account of their superior thermal stability, electrical conductivity and large specific surface area. Although extensive efforts have been devoted to the preparation of 3D Pd-based catalysts with superior activity and stability, designing a simple, effective and eco-friendly method remains a challenge. Herein, we developed a facile one-step coreduction strategy to synthesize a series of 3D surface-wrinkled PdAu nanospheres (NSs) with tunable Pd/Au atomic ratios and found a universal method to prepare surface-wrinkled PdM (M = Au, Pt, Cu and Pb) NSs. Benefiting from the function of the surfactant cetyltrimethylammonium chloride (CTAC), the synthesized PdAu NSs with different composition possess abundant surface wrinkles, which is beneficial for exposing more electroactive centers. Attributed to the unique geometric morphology and optimized atomic ratio, the PdAu-2 NSs exhibited an optimal mass activity (MA) of 8103 mA mg-1 and 5113 mA mg-1 for the ethylene glycol oxidation reaction (EGOR) and ethanol oxidation reaction (EOR), which was 6.1 and 4.1 times that of commercial Pd/C, respectively. Moreover, the PdAu-2 NSs exhibited superb stability after long-term current-time (i-t) and cyclic voltammetry (CV) tests of the EGOR and EOR. This work not only provides new avenues to engineer PdAu NSs with enhanced electrocatalytic performance but also offers guidance for extending to more 3D PdM (M = other metals) NSs with novel morphology applied to fuel cell fields.

Carbon nanotubes encapsulating Pt/MoN heterostructures for superior hydrogen evolution

Achieving efficient hydrogen evolution reaction (HER) catalysts to scale up electrochemical water splitting is desirable but remains a major challenge. Here, nitrogen-doped carbon nanotubes (NCNTs) loaded with PtNi/MoN electrocatalyst (PtNi/MoN@C) is synthesized by a simple strategy to obtain stronger interphase effects and significantly improve HER activity. The surface morphology of the materials is altered by Pt doping and the electronic structure of MoN is changed, which optimizing the electronic environment of the materials, shifting the binding energy and giving the materials a higher electrical conductivity, this ultimately leads to faster proton and electron transfer processes. The synergistic effect of Pt nanoparticles, MoN and the good combination with carbon leads to a high HER activity of 18 mV to reach 10 mA cm-2 in alkaline solution, outperforming that of the commercial Pt/C. Theoretical studies show that the heterostructures can efficiently enhance the electron transport and reduce the △GH*.