Fe-Doped CoP Nanoarray: A Monolithic Multifunctional Catalyst for Highly Efficient Hydrogen Generation

Multimetallic transition metal phosphide nanostructures for supercapacitors and electrochemical water splitting

Transition metal phosphides (TMPs) have recently emerged as an important class of functional materials and been demonstrated to be outstanding supercapacitor electrode materials and catalysts for electrochemical water splitting. While extensive investigations have been devoted to monometallic TMPs, multimetallic TMPs have lately proved to show enhanced electrochemical performance compared to their monometallic counterparts, thanks to the synergistic effect between different transition metal species. This topical review summarizes recent advance in the synthesis of new multimetallic TMP nanostructures, with particular focus on their applications in supercapacitors and electrochemical water splitting. Both experimental reports and theoretical understanding of the synergy between transition metal species are comprehensively reviewed, and perspectives of future research on TMP-based materials for these specific applications are outlined.

Fe Engineering on Ru Nanosheets for Enhanced Hydrogen Evolution in pH-Universal Media

Fe-modified Ru nanosheets are achieved via preintercalated Al species serving as the self-sacrificial template. Benefiting from the amphoteric feature of Al and strong corrosion of Fe³⁺ ions, Fe is effectively incorporated into pristine Ru nanosheets. Correspondingly, the surface oxophilicity is improved, promoting the Volmer step. The charge density redistribution weakens hydrogen combination on Ru and thus accelerates the desorption kinetics (Heyrovsky step). Meanwhile, more defective sites are exposed, leading to an enhanced hydrogen production in pH-universal electrolytes.

Self-supporting nanoporous CoMoP electrocatalyst for hydrogen evolution reaction in alkaline solution

Efficient catalysts with low costs are very important for hydrogen production. In this work, a nanoporous CoMoP (np-CoMoP) bimetallic phosphide catalyst with a self-supporting structure was prepared by the electrochemical dealloying method. The introduction of Mo tuned the electronic structures around Co and P, optimized the desorption of the H atom, and improved the catalytic activity of cobalt phosphide. The prepared nanoporous Co₆₅Mo₁₅P₂₀ (np-Co₆₅Mo₁₅P₂₀) structures promoted electron transfer and provided more active sites, exhibiting superior hydrogen evolution reaction (HER) performance with the overpotential of 40.8 mV at 10 mA cm^-2 and Tafel slope of 46.2 mV dec^-1 in alkaline solution. Also, the catalysts exhibited good long-term stability.

Electronic synergy to boost the performance of NiCoP-NWs@FeCoP-NSs anodes for flexible lithium-ion batteries

Research and development of flexible lithium-ion batteries (LIBs) with high energy density and long cycle life for portable and wearable electronic devices has been a cutting-edge effort in recent years. In this paper, a novel flexible self-standing anode for LIBs is fabricated successfully, in which NiCoP nanowires (NWs) coated with FeCoP nanosheets (NSs) to form core-shell heterostructure arrays are grown on carbon cloth (CC) (designated as NiCoP-NWs@FeCoP-NSs/CC). The obtained NiCoP-NWs@FeCoP-NSs/CC anode integrates the merits of the one-dimensional (1D) NiCoP-NW core and two-dimensional (2D) FeCoP-NS shell and the CC to show a high lithium-ion storage capacity with long-term cycling stability (1172.6 mA h g^-1 at 1 A g^-1 up to 300 cycles with a capacity retention of 92.6%). The kinetics studies demonstrate that the pseudocapacitive behavior dominates the fast lithium storage of this anode material. For fundamental mechanistic understanding, density functional theory (DFT) analysis is carried out, and manifests that electronic synergy can boost the superior performance of the NiCoP-NWs@FeCoP-NSs/CC anode. The assembled LiFePO₄//NiCoP-NWs@FeCoP-NSs/CC full battery gives a discharge capacity of 469.9 mA h g^-1 at 0.5 A g^-1 after 500 cycles, and even at 2 A g^-1, it still can retain 581.5 mA h g^-1. Besides, the soft pack full battery can keep the LED lit continuously when it is folded at different angles and maintain brightness for a period of time, highlighting the large application potential of this flexible LIB for wearable electronic devices. This work provides an idea for the design and construction of advanced metal phosphide flexible electrodes for LIBs.

Ru-doping modulated cobalt phosphide nanoarrays as efficient electrocatalyst for hydrogen evolution rection

Electrochemical water splitting is regarded as a prospective means for H₂ production. The lack of efficient active sites and the sluggish kinetics in alkaline media remain the major obstacles for hydrogen evolution reaction (HER). Herein, a rational construction of Ru-doped cobalt phosphide leaf-like nanoarrays supported on carbon cloth (Ru-CoP NAs) was designed via a MOF-derived route and subsequent phosphating treatment for accelerating HER in the alkaline. The unique hierarchical structure is conductive to exposing more active sites and accelerating the diffusion of electrolyte and the release of H₂ bubble. The optimized Ru-CoP-2.5 NAs exhibits a small overpotential of 52 mV to drive 10 mA cm^-2 for HER and a low Tafel slope of 39.7 mV dec^-1 in 1 M KOH, which outperforms most of other reported CoP-based electrocatalysts. Furthermore, density functional theory (DFT) calculations unveil that Ru dopants can modulate the electron environment around pure CoP and optimize the adsorption energy of H*, accelerating the reaction kinetics. This work provides an insight to promote the electrocatalytic activity of metal phosphide for hydrogen production.

Nanostructured Metal Phosphide Based Catalysts for Electrochemical Water Splitting: A Review

Amongst various futuristic renewable energy sources, hydrogen fuel is deemed to be clean and sustainable. Electrochemical water splitting (EWS) is an advanced technology to produce pure hydrogen in a cost-efficient manner. The electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are the vital steps of EWS and have been at the forefront of research over the past decades. The low-cost nanostructured metal phosphide (MP)-based electrocatalysts exhibit unconventional physicochemical properties and offer very high turnover frequency (TOF), low over potential, high mass activity with improved efficiency, and long-term stability. Therefore, they are deemed to be potential electrocatalysts to meet practical challenges for supporting the future hydrogen economy. This review discusses the recent research progress in nanostructured MP-based catalysts with an emphasis given on in-depth understanding of catalytic activity and innovative synthetic strategies for MP-based catalysts through combined experimental (in situ/operando techniques) and theoretical investigations. Finally, the challenges, critical issues, and future outlook in the field of MP-based catalysts for water electrolysis are addressed.

Steps towards highly-efficient water splitting and oxygen reduction using nanostructured β-Ni(OH)2

β-Ni(OH)2 nanoplatelets are prepared by a hydrothermal procedure and characterized by scanning and transmission electron microscopy, X-ray diffraction analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. The material is demonstrated to be an efficient electrocatalyst for oxygen reduction, oxygen evolution, and hydrogen evolution reactions in alkaline media. β-Ni(OH)2 shows an overpotential of 498 mV to reach 10 mA cm-2 towards oxygen evolution, with a Tafel slope of 149 mV dec-1 (decreasing to 99 mV dec-1 at 75 °C), along with superior stability as evidenced by chronoamperometric measurements. Similarly, a low overpotential of -333 mV to reach 10 mA cm-2 (decreasing to only -65 mV at 75 °C) toward hydrogen evolution with a Tafel slope of -230 mV dec-1 is observed. Finally, β-Ni(OH)2 exhibits a noteworthy performance for the ORR, as evidenced by a low Tafel slope of -78 mV dec-1 and a number of exchanged electrons of 4.01 (indicating direct 4e--oxygen reduction), whereas there are only a few previous reports on modest ORR activity of pure Ni(OH)2.

Heterostructured CoP·CoMoP nanocages as advanced electrocatalysts for efficient hydrogen evolution over a wide pH range

A sustainable and environmental-friendly method to produce hydrogen with high purity is the electrochemical water splitting, but its commercialization is challenged due to lack of cost-effective electrocatalysts for hydrogen evolution reaction (HER) over a wide pH range. Herein, a series of CoP·xCoMoP heterostructured nanocages (NCs) were prepared via a dissolution-regrowth and subsequent phosphorization process using metal-organic frameworks (MOFs) as template. The three-dimensional (3D) architecture of CoP·xCoMoP is constituted by the heterostructured nanosheets composed with CoP and CoMoP phase. These noble-metal-free earth-abundant transition metal phosphide (TMP) catalysts show a pH-universal HER activity with high efficiency. Under the optimal atom ratio of Co and Mo (6:5), CoP·5CoMoP NC catalysts can deliver a current density of 10 mA cm^-2 at the overpotential of 72 mV with a Tafel slope of 60.3 mV dec^-1 in 1.0 M KOH solution. The same current output requires overpotential of 44 mV in 0.5 M H₂SO₄ solution and 151 mV in1.0 M phosphate buffered solution (PBS), respectively. The superior HER activity of CoP·5CoMoP NC catalysts can be comparable to or even better than most of noble metal-free HER electrocatalysts reported recently. In addition, CoP·5CoMoP NC catalysts also show a fairly high HER stability over a wide pH range, and their HER activity can be well kept without significant loss for long-term electrolysis. The 3D CoP·5CoMoP heterostructured catalysts hold promise as efficient and low-cost catalysts for water splitting devices over a wide pH range.

Ni2P nanosheet array for high-efficiency electrohydrogenation of nitrite to ammonia at ambient conditions

Ammonia (NH₃) plays an important role in agriculture and industry. The industry-scale production mainly depends on the Haber-Bosch process suffering from issues of environment pollution and energy consumption. Electrochemical reduction can degrade nitrite (NO₂^-) pollutants in the environment and convert it into more valuable NH₃. Here, Ni₂P nanosheet array on nickel foam is proposed as a 3D electrocatalyst for high-efficiency electrohydrogenation of NO₂^- to NH₃ under ambient reaction conditions. When tested in 0.1 M phosphate buffer saline with 200 ppm NO₂^-, such Ni₂P/NF is able to obtain a large NH₃ yield rate of 2692.2 ± 92.1 μg h^-1 cm^-2 (3282.9 ± 112.3 μg h^-1 mg_cat.^-1), a high Faradic efficiency of 90.2 ± 3.0%, and selectivity of 87.0 ± 1.7% at -0.3 V versus a reversible hydrogen electrode. After 10 h of electrocatalytic reduction, the conversion rate of NO₂^- achieves near 100%. The catalytic mechanism is further investigated by density functional theory calculations.

An efficient vanadium/cobalt metaphosphate electrocatalyst for hydrogen and oxygen evolution in alkaline water splitting

Hydrogen, which meets the goal of carbon neutrality, is expected to replace conventional fossil fuels in the near future. Electrochemical water splitting is a clean hydrogen production technology, but its...

Fe-CoP/C composite nanoplate derived from 2D porphyrin MOF as an efficient catalyst for oxygen evolution reaction

The 2D Fe-CoP/C composite transformed from 2D PPF-5-Fe/Co MOF presents a high activity for the oxygen evolution reaction in alkaline media.

Surface engineered CoP/Co3O4 heterojunction for high-performance bi-functional water splitting electro-catalysis

In the electrochemical water splitting process, integrating hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the same electrolyte with the same catalyst is highly beneficial for increasing the energy efficiency and reducing the fabrication cost. However, most OER catalysts are unstable in the acidic solution, while HER shows poor kinetics in the alkaline solution, which hinders the scale-up application of electro-catalytic water splitting. In this work, a CoP/Co₃O₄ heterostructure is firstly fabricated and then O and P defects are introduced via surface engineering (s-CoP/Co₃O₄). The as-prepared material was employed as the catalyst towards electrochemical water splitting in an alkaline environment. In alkaline HER, a current density of -10 mA cm^-2 can be achieved at an overpotential of 106 mV vs. RHE. In the OER process, the overpotential of s-CoP/Co₃O₄ electrode is only 211 mV vs. RHE at 10 mA cm^-2 in 1 M KOH, and the corresponding Tafel slope is only 58.4 mV dec^-1 so that the s-CoP/Co₃O₄ electrode could be used as the bifunctional catalyst for alkaline water splitting. This work provides a simple and low-cost approach to fabricate a Co-based heterojunction electrode with unsaturated metal sites to improve the electro-catalytic activities towards water splitting.

One-dimensional CoP/MnO hollow nanostructures with enhanced oxygen evolution reaction activity

Cobalt-based transition metal phosphides are flourishing as OER electrocatalysts. In this study, the CoP/MnO hollow nanofibers with the advantages of a more extensive contact interface were successfully synthesized. We found that the construction of hollow nanostructures and the composite of oxides are effective strategies to optimize the OER catalytic performance of transition metal phosphides. The template of the precursor can adjust the hollow nanostructure and keep it stable during the phosphating process. It is worth noting that the CoP/MnO composite material only needs an overpotential of 230 mV at a current density of 10 mA cm^-2. In addition, it maintains the overpotential 263.5 mV after 5000 cycles of voltammetry measurements. In short, this research provides a simple solution for the design and realization of nanostructured electrocatalysts with excellent electrochemical performance.

Atomically ordered Rh2P catalysts anchored within hollow mesoporous carbon for efficient hydrogen production

Atomically ordered Rh₂P nanoclusters encapsulated within a high-surface-area hollow mesoporous carbon nanoreactor are catalytically active for hydrogen production via the electrocatalytic hydrogen evolution reaction and the room-temperature dehydrogenation of ammonia borane.

In Situ Fabrication of Nickel-Iron Oxalate Catalysts for Electrochemical Water Oxidation at High Current Densities

Ni-Fe-based electrode materials are promising candidates for the oxygen evolution reaction (OER). The synergy between Fe and Ni atoms is crucial in modulating the electronic structure of the active site to enhance electrochemical performance. Herein, a simple chemical immersion technique was used to grow Ni-Fe oxalate nanowires directly on a porous nickel foam substrate. The as-prepared Ni-Fe oxalate electrode exhibited an excellent electrochemical performance of the OER with ultralow overpotentials of 210 and 230 mV to reach 50 and 100 mA cm-2 current densities, respectively, in a 1 M KOH aqueous solution. The excellent OER performance of this Ni-Fe oxalate electrode can be attributed to its bimetallic composition and nanowire structure, which leads to an efficient ionic diffusion, high electronic conductivity, and fast electron transfer. The overall analysis indicates a suitable approach for designing electrocatalysts applicable in energy conversion.

Zeolitic Imidazolate Framework-67-Derived P-Doped Hollow Porous Co3O4 as a Photocatalyst for Hydrogen Production from Water

As a part of photocatalytic water splitting, the design of low-cost, high-activity catalysts plays an essential role in the development of photocatalytic water splitting. Metal oxides have the advantages of a wide range of sources, many varieties, and easy preparation. Doping engineering on their surface can construct new active sites and adjust their catalytic activity. In this work, a new strategy was developed through anion hybridization to regulate electron delocalization. Using one of the cobalt-based zeolitic imidazole skeletons (ZIF-67) as a precursor material, a two-step calcination method was used to prepare a P-doped Co₃O₄ mixed anion composite photocatalyst. The hydrogen production rate of P@Co₃O₄ is 39 times that of ZIF-67 and 6.8 times that of Co₃O₄. Through density functional theory (DFT) calculations, the electron delocalization state of the sample surface is predicted and the reaction energy barrier is reduced to promote the process of the hydrogen evolution reaction (HER). The special O(δ-)-Co(δ+)-P(δ-) surface bonding state promotes the bridging of isolated electronic states and provides active sites for the adsorption and activation of reaction substrates. The improved electron transport pathway and the synergy between the catalytic sites under the high electron transport rate are the main reasons for the enhanced photocatalytic hydrogen evolution activity. This strategy, including changing the surface bond state and optimizing the structure and composition of the catalyst not only provides a new method for preparing other MOF-derived nanomaterials with porous structures but also inspires the reasonable development of other MOF-based advanced photocatalysts.

Nanostructured Metal Borides for Energy-Related Electrocatalysis: Recent Progress, Challenges, and Perspectives

The discovery of durable, active, and affordable electrocatalysts for energy-related catalytic applications plays a crucial role in the advancement of energy conversion and storage technologies to achieve a sustainable energy future. Transition metal borides (TMBs), with variable compositions and structures, present a number of interesting features including coordinated electronic structures, high conductivity, abundant natural reserves, and configurable physicochemical properties. Therefore, TMBs provide a wide range of opportunities for the development of multifunctional catalysts with high performance and long durability. This review first summarizes the typical structural and electronic features of TMBs. Subsequently, the various synthetic methods used thus far to prepare nanostructured TMBs are listed. Furthermore, advances in emerging TMB-catalyzed reactions (both theoretical and experimental) are highlighted, including the hydrogen evolution reaction, the oxygen evolution reaction, the oxygen reduction reaction, the carbon dioxide reduction reaction, the nitrogen reduction reaction, the methanol oxidation reaction, and the formic acid oxidation reaction. Finally, challenges facing the development of TMB electrocatalysts are discussed, with focus on synthesis and energy-related catalytic applications, and some potential strategies/perspectives are suggested as well, which will profit the design of more efficient TMB materials for application in future energy conversion and storage devices.

Hierarchical Double-Shelled CoP Nanocages for Efficient Visible-Light-Driven CO2 Reduction

Visible-light-driven photocatalytic CO₂ reduction is considered an appealing strategy to mitigate the energy crisis and environmental issues, whereas the reactivity is limited due to the difficulties in activation of inert CO₂ molecule and efficient transportation of photoinduced carriers. Herein, we report the design of novel Fe doped CoP hierarchical double-shelled nanocages (Fe-CoP HDSNC) via a MOF-templated approach for highly efficient visible-light-driven CO₂ reduction. The unique hierarchical double-shelled hollow architectures can greatly shorten the charge transfer distances and also expose abundant reactive sites. Moreover, Fe atoms doping is able to reduce the CO₂ activation energy barrier through stabilizing the *COOH intermediates and promote the CO desorption by destabilizing the CO* adduct. As expected, the Fe-CoP HDSNC achieves an unprecedented catalytic efficiency in visible-light-driven CO₂ reduction with an up to 3.25% apparent quantum yield and 90.3% CO selectivity, superior to most of the state-of-the-art photocatalysts under comparable conditions. More importantly, the Fe-CoP HDSNC is also highly effective under diluted CO₂ atmosphere, suggesting the practicability of the present photocatalytic system.

Activity Promotion of Core and Shell in Multifunctional Core-Shell Co2 P@NC Electrocatalyst by Secondary Metal Doping for Water Electrolysis and Zn-Air Batteries

Developing cost-efficient multifunctional electrocatalysts is highly critical for the integrated electrochemical energy-conversion systems such as water electrolysis based on hydrogen/oxygen evolution reactions (HER/OER) and metal-air batteries based on OER/oxygen reduction reactions (ORR). The core-shell structured materials with transition metal phosphide as the core and nitrogen-doped carbon (NC) as the shell have been known as promising HER electrocatalysts. However, their oxygen-related electrocatalytic activities still remain unsatisfactory, which severely limits their further applications. Herein an effective strategy to improve the core and shell performances of core-shell Co₂ P@NC electrocatalysts through secondary metal (e.g., Fe, Ni, Mo, Al, Mn) doping (termed M-Co₂ P@M-N-C) is reported. The as-synthesized M-Co₂ P@M-N-C electrocatalysts show multifunctional HER/OER/ORR activities and good integrated capabilities for overall water splitting and Zn-air batteries. Among the M-Co₂ P@M-N-C catalysts, Fe-Co₂ P@Fe-N-C electrocatalyst exhibits the best catalytic activities, which is closely related to the configuration of highly active species (Fe-doping Co₂ P core and Fe-N-C shell) and their subtle synergy, and a stable carbon shell for outstanding durability. Combination of electrochemical-based in situ Fourier transform infrared spectroscopy with extensive experimental investigation provides deep insights into the origin of the activity and the underlying electrocatalytic mechanisms at the molecular level.

Electrocatalytic deep dehalogenation of florfenicol using Fe-doped CoP nanotubes array for blocking resistance gene expression and microbial inhibition during biochemical treatment

Resistance gene expression and microbial inhibition by halogenated antibiotics is a major environmental concern. Although electrocatalytic dehalogenation can detoxify halogenated antibiotics, the effect of dehalogenation treatment on resistance gene expression and microbial inhibition is poorly understood. Herein, a novel electrocatalyst of Fe-doped CoP nanotubes array on nickel foam (Fe-CoP NTs/NiF) is prepared through a simple ultrasonication of Fe-doped CoP nanowires hydrothermally grown on NiF. The transformation from nanowires to nanotubes improves the crystallinity of CoP and fully exposes active sites, producing energetic atomic hydrogen for dehalogenation. Fe-CoP NTs/NiF exhibits a superior dehalogenation performance towards refractory florfenicol (FLO), achieving 100% removal within 20 min (‒1.2 V vs Ag/AgCl, C₀ = 20 mg L^‒1). The dechlorination ratio reaches nearly 100%, and the defluorination ratio achieves 36.8% within 50 min, showing the best electrocatalytic dehalogenation performance reported so far. Microbial community and correlation analysis show that Proteobacteria is the main potential host of FLO resistance gene. Electrocatalytic reductive dehalogenation pretreatment of FLO can reduce microbial inhibition, maintaining microbial richness and diversity in the subsequent biochemical treatment unit. The electrocatalytic reductive dehalogenation treatment can significantly reduce the relative abundance of FLO resistance gene, showing a reliable process for safe treatment of halogenated antibiotic containing wastewater.

Synergistically integrated Co9S8@NiFe-layered double hydroxide core-branch hierarchical architectures as efficient bifunctional electrocatalyst for water splitting

Efficient, low-cost, and robust electrocatalysts development for overall water splitting is highly desirable for renewable energy production yet still remains challenging. In this work, Co₉S₈ nanoneedles arrays are synergistically integrated with NiFe-layered double hydroxide (NiFe-LDH) nanosheets to form Co₉S₈@NiFe-LDH core-branch hierarchical architectures supported on nickel foam (Co₉S₈@NiFe-LDH HAs/NF). The Co₉S₈@NiFe-LDH HAs/NF exhibits high catalytic performances for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with overpotential of 190 and 145 mV at 10 mA cm^-2, respectively. The density functional theory calculations predict that the synergy between Co₉S₈ and NiFe-LDH contributes to the high catalytic performance by lowering the energy barrier of HER. When used as both anode and cathode electrocatalyst, it can deliver 10 mA cm^-2 at a low cell voltage of 1.585 V with excellent long-term durability. This work opens a new avenue toward the exploration of highly efficient and stable electrocatalyst for overall water splitting.

A membrane-free flow electrolyzer operating at high current density using earth-abundant catalysts for water splitting

Electrochemical water splitting is one of the most sustainable approaches for generating hydrogen. Because of the inherent constraints associated with the architecture and materials, the conventional alkaline water electrolyzer and the emerging proton exchange membrane electrolyzer are suffering from low efficiency and high materials/operation costs, respectively. Herein, we design a membrane-free flow electrolyzer, featuring a sandwich-like architecture and a cyclic operation mode, for decoupled overall water splitting. Comprised of two physically-separated compartments with flowing H2-rich catholyte and O2-rich anolyte, the cell delivers H2 with a purity >99.1%. Its low internal ohmic resistance, highly active yet affordable bifunctional catalysts and efficient mass transport enable the water splitting at current density of 750 mA cm-2 biased at 2.1 V. The eletrolyzer works equally well both in deionized water and in regular tap water. This work demonstrates the opportunity of combining the advantages of different electrolyzer concepts for water splitting via cell architecture and materials design, opening pathways for sustainable hydrogen generation.

Iron Phthalocyanine/Two-Dimensional Metal-Organic Framework Composite Nanosheets for Enhanced Alkaline Hydrogen Evolution

Hydrogen evolution reaction (HER) in alkaline medium is currently under scientific spotlight for generating clean H₂ fuel from electrochemical water splitting. However, alkaline HER suffers from sluggish reaction kinetics because of the additional energy required for water dissociation from catalysts in contrast to acidic HER. Herein, we report the development of two-dimensional metal-organic framework (2D MOF) Ni-1,4-benzenedicarboxylic acid-based composite nanosheets for superior performance in HER electrocatalysis. Iron phthalocyanine (FePc) molecules are uniformly anchored on the ultrathin 2D Ni-MOF, showing a substantially increased current density, improved activity, and enhanced durability in alkaline HER. On account of the ultralarge specific surface of Ni-MOF and the coupling effects between FePc and 2D MOFs, the resultant nanosheet catalyst FePc@Ni-MOF exhibits a low overpotential (334 mV) and satisfactory long-term stability (10 h) at a current density of 10 mA·cm^-2, which outperform those of pristine FePc, Ni-MOF, and the counterpart FePc@bulk-MOF. This study provides new insights into the synthesis of robust MOF-based nanosheet composites with high performance in catalysis.

"Superaerophobic" NiCo bimetallic phosphides for highly efficient hydrogen evolution reaction electrocatalysts

A "superaerophobic" NiCo bimetallic phosphide electrocatalyst has been fabricated by employing bimetal-organic frameworks as self-sacrificing templates. An overpotential of only 205 mV can drive the HER current density to 800 mA cm-2, which is even superior to that for Pt/C. This study provides a promising approach for the development of industrialized HER electrocatalysts.

Electronic Structure and d-Band Center Control Engineering over Ni-Doped CoP3 Nanowall Arrays for Boosting Hydrogen Production

To address the challenge of highly efficient water splitting into H₂, successful fabrication of novel porous three-dimensional Ni-doped CoP₃ nanowall arrays on carbon cloth was realized, resulting in an effective self-supported electrode for the electrocatalytic hydrogen-evolution reaction. The synthesized samples exhibit rough, curly, and porous structures, which are beneficial for gaseous transfer and diffusion during the electrocatalytic process. As expected, the obtained Ni-doped CoP₃ nanowall arrays with a doping concentration of 7% exhibit the promoted electrocatalytic activity. The achieved overpotentials of 176 mV for the hydrogen-evolution reaction afford a current density of 100 mA cm⁻², which indicates that electrocatalytic performance can be dramatically enhanced via Ni doping. The Ni-doped CoP₃ electrocatalysts with increasing catalytic activity should have significant potential in the field of water splitting into H₂. This study also opens an avenue for further enhancement of electrocatalytic performance through tuning of electronic structure and d-band center by doping.

A fundamental viewpoint on the hydrogen spillover phenomenon of electrocatalytic hydrogen evolution

Hydrogen spillover phenomenon of metal-supported electrocatalysts can significantly impact their activity in hydrogen evolution reaction (HER). However, design of active electrocatalysts faces grand challenges due to the insufficient understandings on how to overcome this thermodynamically and kinetically adverse process. Here we theoretically profile that the interfacial charge accumulation induces by the large work function difference between metal and support (∆Φ) and sequentially strong interfacial proton adsorption construct a high energy barrier for hydrogen transfer. Theoretical simulations and control experiments rationalize that small ∆Φ induces interfacial charge dilution and relocation, thereby weakening interfacial proton adsorption and enabling efficient hydrogen spillover for HER. Experimentally, a series of Pt alloys-CoP catalysts with tailorable ∆Φ show a strong ∆Φ-dependent HER activity, in which PtIr/CoP with the smallest ∆Φ = 0.02 eV delivers the best HER performance. These findings have conclusively identified ∆Φ as the criterion in guiding the design of hydrogen spillover-based binary HER electrocatalysts.

Ultrathin Trimetal-Organic Framework Nanosheet Electrocatalysts for the Highly Efficient Oxygen Evolution Reaction

Synthesis of ultrathin metal-organic framework (MOF) nanosheets for highly efficient oxygen evolution reaction (OER) is prevalent, but still many challenges remain. Herein, a facile and efficient three-layer method is reported for the synthesis of NiCoFe-based trimetallic MOF nanosheets, which can be directly used for the oxygen evolution reaction in alkaline conditions. The physical characterization and morphology of trimetallic MOF nanosheets were characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). By optimizing the molar ratio of Ni/Co/Fe atoms, a series of MOFs with different metal proportions were synthesized. Among them, the as-prepared (Ni₃Co₁)₃Fe₁-MOF nanosheets can deliver a current density of 10 mA cm^-2 at a low overpotential of 245 mV with a small Tafel slope of 50.9 mV dec^-1 in an alkaline electrolyte and exhibit excellent stability. More importantly, through the characterization of the intermediates in the OER process, the possible source of the catalytic active species is the electrochemically transformed metal hydroxides and oxyhydroxides.

Two-dimension on two-dimension growth: hierarchical Ni0.2Mo0.8N/Fe-doped Ni3N nanosheet array for overall water splitting

Developing advanced electrocatalysts with low cost for electrocatalytic water splitting are highly desirable. Herein, we report the design of two-dimension on two-dimension growth of hierarchical Ni0.2Mo0.8N nanosheets on Fe-doped Ni3N nanosheets supported on Ni foam (Ni0.2Mo0.8N/Fe-Ni3N/NF) via hydrothermal reaction and nitridation treatment. In the hierarchical structures, small Ni0.2Mo0.8N nanosheets were uniformly anchored on Fe-Ni3N nanosheets. Due to enhanced electron transfer between Ni0.2Mo0.8N and Fe-Ni3N, Ni0.2Mo0.8N/Fe-Ni3N/NF exhibits superior electrocatalytic activity for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). After stability tests for 50 h, Ni0.2Mo0.8N/Fe-Ni3N/NF exhibits negligible degradation of the current density for the OER (91% remain) and HER (95% remain), suggesting excellent stability. Owing to the outstanding performance, Ni0.2Mo0.8N/Fe-Ni3N/NF display a cell voltage of 1.54 V (10 mA cm-2) for electrocatalytic overall water splitting.

Boosting Hydrazine Oxidation Reaction on CoP/Co Mott-Schottky Electrocatalyst through Engineering Active Sites

The hydrazine oxidation reaction (HzOR), as a substitute for the sluggish oxygen evolution reaction (OER), is identified as a promising powerfrugal strategy for hydrogen production through water splitting. However, the HzOR activity of the present electrocatalysts is unsatisfying because the work potential is much higher than the theoretical value. Herein, we design a typical Mott-Schottky electrocatalyst consisting of CoP/Co nanoparticles for the HzOR, which exhibits remarkable HzOR activity with ultralow potentials of -69 and 177 mV at 10 and 100 mA cm^-2, respectively. It stands out in a range of cobalt-based materials and is even comparable to some precious-metal-based materials composed of Pt or Ru. A shown by with structural characterization and density functional theory (DFT) calculations, the interfaces between CoP/Co nanoparticles not only provide the active sites of HzOR but also promote the multistep dehydrogenation reaction of N₂H₄, thus enhancing the HzOR activity.

Transition Metal-Based 2D Layered Double Hydroxide Nanosheets: Design Strategies and Applications in Oxygen Evolution Reaction

Water splitting driven by renewable energy sources is considered a sustainable way of hydrogen production, an ideal fuel to overcome the energy issue and its environmental challenges. The rational design of electrocatalysts serves as a critical point to achieve efficient water splitting. Layered double hydroxides (LDHs) with two-dimensionally (2D) layered structures hold great potential in electrocatalysis owing to their ease of preparation, structural flexibility, and tenability. However, their application in catalysis is limited due to their low activity attributed to structural stacking with irrational electronic structures, and their sluggish mass transfers. To overcome this challenge, attempts have been made toward adjusting the morphological and electronic structure using appropriate design strategies. This review highlights the current progress made on design strategies of transition metal-based LDHs (TM-LDHs) and their application as novel catalysts for oxygen evolution reactions (OERs) in alkaline conditions. We describe various strategies employed to regulate the electronic structure and composition of TM-LDHs and we discuss their influence on OER performance. Finally, significant challenges and potential research directions are put forward to promote the possible future development of these novel TM-LDHs catalysts.

Synergistic effects of Fe and Mn dual-doping in Co3S4 ultrathin nanosheets for high-performance hybrid supercapacitors

Dopant engineering in nanostructured materials is an effective strategy to enhance electrochemical performances via regulating the electronic structures and achieving more active sites. In this work, a robust electrode based on Fe and Mn co-doped Co₃S₄ (FM-Co₃S₄) ultrathin nanosheet arrays (NSAs) on the Ni foam substrate is prepared through a facile hydrothermal method followed by a subsequent sulfurization reaction. It has been found that the incorporation of Fe ions is beneficial to higher specific capacity of the final electrode and Mn ions contribute to the excellent rate capability in the reversible redox processes. Density functional theory (DFT) calculations further verify that the Mn doping in the Co₃S₄ obviously shorten the energy gap of Co₃S₄, which favors the electrochemical performances. Due to the synergetic effects of different transition metal ions, the as-prepared FM-Co₃S₄ ultrathin NSAs exhibit a high specific capacity of 390 mAh g^-1 at 5 A g^-1, as well as superior rate capability and excellent cycling stability. Moreover, the corresponding quasi-solid-state hybrid supercapacitors constructed with the FM-Co₃S₄ ultrathin NSAs and active carbon exhibit a high energy density of 55 Wh kg^-1 at the power density of 752 W kg^-1. These findings demonstrate a new platform for developing high-performance electrodes for energy storage applications.

Spatially Confined Formation of Single Atoms in Highly Porous Carbon Nitride Nanoreactors

Reducing the size of a catalyst to a single atom (SA) level can dramatically change its physicochemical properties and significantly boost its catalytic activity. However, the massive synthesis of SA catalysts still remains a grand challenge mainly because of the aggregation and nucleation of the generated atoms during the reaction. Here, we design and implement a spatially confined synthetic strategy based on a porous-hollow carbon nitride (p-CN) coordinated with 1-butyl-3-methylimidazole hexafluorophosphate, which can act as a nanoreactor and allow us to obtain metal SA catalysts (p-CN@M SAs). This relatively easy and highly effective method provides a way to massively synthesize single/multiple atoms (p-CN@M SAs, M = Pt, Pd, Cu, Fe, etc.). Moreover, the amorphous NiB-coated p-CN@Pt SAs can further increase the loading amount of Pt SAs to 3.7 wt %. The synthesized p-CN@Pt&NiB electrocatalyst exhibits an extraordinary hydrogen evolution reaction activity with the overpotential of 40.6 mV@10 mA/cm^-2 and the Tofel slope of 29.26 mV/dec.

Ordered clustering of single atomic Te vacancies in atomically thin PtTe2 promotes hydrogen evolution catalysis

Exposing and stabilizing undercoordinated platinum (Pt) sites and therefore optimizing their adsorption to reactive intermediates offers a desirable strategy to develop highly efficient Pt-based electrocatalysts. However, preparation of atomically controllable Pt-based model catalysts to understand the correlation between electronic structure, adsorption energy, and catalytic properties of atomic Pt sites is still challenging. Herein we report the atomically thin two-dimensional PtTe₂ nanosheets with well-dispersed single atomic Te vacancies (Te-SAVs) and atomically well-defined undercoordinated Pt sites as a model electrocatalyst. A controlled thermal treatment drives the migration of the Te-SAVs to form thermodynamically stabilized, ordered Te-SAV clusters, which decreases both the density of states of undercoordinated Pt sites around the Fermi level and the interacting orbital volume of Pt sites. As a result, the binding strength of atomically defined Pt active sites to H intermediates is effectively reduced, which renders PtTe₂ nanosheets highly active and stable in hydrogen evolution reaction.

Precisely regulating Pt catalytic sites is important and challenging. Herein the authors engineer the clustering of single atomic Te vacancies in atomically thin PtTe₂ to optimize the electronic structure, adsorption energy, and catalytic performance of atomically defined Pt sites.

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

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

Multi-Phase Heterostructure of CoNiP/Cox P for Enhanced Hydrogen Evolution Under Alkaline and Seawater Conditions by Promoting H2 O Dissociation

Hydrogen evolution reaction (HER) is a key step for electrochemical energy conversion and storage. Developing well defined nanostructures as noble-metal-free electrocatalysts for HER is promising for the application of hydrogen technology. Herein, it is reported that 3D porous hierarchical CoNiP/Co_x P multi-phase heterostructure on Ni foam via an electrodeposition method followed by phosphorization exhibits ultra-highly catalytic activity for HER. The optimized CoNiP/Co_x P multi-phase heterostructure achieves an excellent HER performance with an ultralow overpotential of 36 mV at 10 mA cm^-2 , superior to commercial Pt/C. Importantly, the multi-phase heterostructure shows exceptional stability as confirmed by the long-term potential cycles (30,000 cycles) and extended electrocatalysis (up to 500 h) in alkaline solution and natural seawater. Experimental characterizations and DFT calculations demonstrate that the strong electronic interaction at the heterointerface of CoNiP/CoP is achieved via the electron transfer from CoNiP to the heterointerface, which directly promotes the dissociation of water at heterointerface and desorption of hydrogen on CoNiP. These findings may provide deep understanding on the HER mechanism of heterostructure electrocatalysts and guidance on the design of earth-abundant, cost-effective electrocatalysts with superior HER activity for practical applications.