Integration of morphology and electronic structure modulation on cobalt phosphide nanosheets to boost photocatalytic hydrogen evolution from ammonia borane hydrolysis

The controllable and safe hydrogen storage technologies are widely recognized as the main bottleneck for the accomplishment of sustainable hydrogen energy.Ammonia borane(AB)has regarded as a competitive candidate for chemical hydrogen storage.However,developing efficient yet high-performance catalysts towards hydrogen evolution from AB hydrolysis remains an enormous challenge.Herein,cobalt phosphide nanosheets are synthesized by a facile salt-assisted along with low-temperature phosphidation strategy for simultaneously modulating its morphology and electronic structure,and function as hydrogen evolution photocatalysts.Impressively,the Co_(2)P nanosheets display extraordinary performance with a record high turnover frequency of 44.9 min^(-1),outperforming most of the noble-metal-free catalysts reported to date.This remarkable performance is attributed to its desired nanosheets structure,featuring with high specific surface area,abundant exposed active sites,and short charge diffusion paths.Our findings provide a novel strategy for regulating metal phosphides with desired phase structure and morphology for energy-related applications and beyond.

MOF-Derived Iron-Cobalt Phosphide Nanoframe as Bifunctional Electrocatalysts for Overall Water Splitting

Transition metal phosphides(TMPs)have emerged as an alternative to precious metals as efficient and low-cost catalysts for water electrolysis.Elemental doping and morphology control are effective approaches to further improve the performance of TMPs.Herein,Fe-doped CoP nanoframes(Fe-CoP NFs)with specific open cage configuration were designed and synthesized.The unique nano-framework structured Fe-CoP material shows overpotentials of only 255 and 122 mV at 10 mA cm^(−2)for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER),respectively,overwhelming most transition metal phosphides.For overall water splitting,the cell voltage is 1.65 V for Fe-CoP NFs at a current density of 10 mA cm^(−2),much superior to what is observed for the classical nanocubic structures.Fe-CoP NFs show no activity degradation up to 100 h which contrasts sharply with the rapidly decaying performance of noble metal catalyst reference.The superior electrocatalytic performance of Fe-CoP NFs due to abundant accessible active sites,reduced kinetic energy barrier,and preferable*O-containing intermediate adsorption is demonstrated through experimental observations and theoretical calculations.Our findings could provide a potential method for the preparation of multifunctional material with hollow structures and offer more hopeful prospects for obtaining efficient earth-abundant catalysts for water splitting.

Enhancing water-dissociation kinetics and optimizing intermediates adsorption free energy of cobalt phosphide via high-valence Zr incorporating for alkaline water electrolysis

Developing high-efficiency electrocatalysts for hydrogen evolution reaction(HER) and oxygen evolution reaction(OER) is required to enhance the sluggish kinetics of water dissociation and optimize the adsorption free energy of reaction intermediates.Herein,we tackle this challenge by incorporating high-valence Zr into CoP(ZrxCo_(1-x)P),which significantly accelerates the elementary steps of water electrolysis.Theoretical calculations indicate that the appropriate Zr incorporation effectively expedites the sluggish H2O dissociation kinetics and optimizes the adsorption energy of reaction intermediates for boosting the alkaline water electrolysis.These are confirmed by the experimental results of Zr_(0.06)Co_(0.94)P catalyst that delivers exceptional electrochemical activity.The overpotentials at the current density of 10 mA cm^(-2)(j10) are only 62(HER) and 240 mV(OER) in alkaline media.Furthermore,the Zr_(0.06)Co_(0.94)P/CC‖Zr_(0.06)Co_(0.94)P/CC system exhibits superior overall water splitting activity(1.53 V/j10),surpassing most of the reported bifunctional catalysts.This high-valence Zr incorporation and material design methods explore new avenues for realizing high-performance non-noble metal electrocatalysts.

In-situ formation of cobalt phosphide nanoparticles confined in three-dimensional porous carbon for high-performing zinc-air battery and water splitting

The rational design of efficient and stable carbon-based electrocatalysts for oxygen reduction and oxygen evolution reactions is crucial for improving energy density and long-term stability of rechargeable zinc-air batteries(ZABs).Herein,a general and controllable synthesis method was developed to prepare three-dimensional(3D)porous carbon composites embedded with diverse metal phosphide nanocrystallites by interfacial coordination of transition metal ions with phytic acid-doped polyaniline networks and subsequent pyrolysis.Phytic acid as the dopant of polyaniline provides favorable anchoring sites for metal ions owing to the coordination interaction.Specifically,adjusting the concentration of adsorbed cobalt ions can achieve the phase regulation of transition metal phosphides.Thus,with abundant cobalt phosphide nanoparticles and nitrogen-and phosphorus-doping sites,the obtained carbon-based electrocatalysts exhibited efficient electrocatalytic activities toward oxygen reduction and evolution reactions.Consequently,the fabricated ZABs exhibited a high energy density,high power density of 368 mW cm^(-2),and good cycling/mechanical stability,which could power water splitting for integrated device fabrication with high gas yields.

Arrayed Cobalt Phosphide Electrocatalyst Achieves Low Energy Consumption and Persistent H2 Liberation from Anodic Chemical Conversion

Electrochemical reduction of water to hydrogen(H2) offers a promising strategy for production of clean energy,but the design and optimization of electrochemical apparatus present challenges in terms of H2 recovery and energy consumption.Using cobalt phosphide nanoarrays(Co2 P/CoP NAs) as a charge mediator,we effectively separated the H2 and O2 evolution of alkaline water electrolysis in time,thereby achieving a membrane-free pathway for H2 purification.The hierarchical array structure and synergistic optimization of the electronic configuration of metallic Co2 P and metalloid CoP make the Co2 P/CoP NAs high-efficiency bifunctional electrocatalysts for both charge storage and hydrogen evolution.Theoretical investigations revealed that the introduction of Co2 P into CoP leads to a moderate hydrogen adsorption free energy and low water dissociation barrier,which are beneficial for boosting HER activity.Meanwhile,Co2 P/CoP NAs with high capacitance could maintain a cathodic H2 evolution time of 1500 s at 10 mA cm^(-2) driven by a low average voltage of 1.38 V.Alternatively,the energy stored in the mediator could be exhausted via coupling with the anodic oxidation of ammonia,whereby only 0.21 V was required to hold the current for 1188 s.This membrane-free architecture demonstrates the potential for developing hydrogen purification technology at low cost.

High-performance sodium storage for cobalt phosphide composite array electrodes

Transition metal phosphides hold great potential as sodium-ion batteries anode materials owing to their high theoretical capacity and modest plateau.However,volume changes and low intrinsic conductivity seriously largely hinder the further development of metal phosphide anodes.The design of phosphide anode materials with reasonable structure is conducive to solving the problems of volume expansion and slow reaction kinetics during the reaction.In this work,a composite material integrating zeolite imidazolate backbone(ZIF) and carbon materials was synthesized by the original growth method.Furthermore,by the oxidation-phosphating process,CoP nanoarray composites riveted to carbon fiber(CoP@CF) were obtained.In the CoP@CF,CoP nanoparticles are uniformly distributed on ZIF-derived carbon,reducing agglomeration and volume change during cycling.CF also provides a highly conductive network for the active material,improving the electrode kinetics.Therefore,when evaluated as an anode for sodium-ion batteries,CoP@CF electrode displays enhanced reversible capacity(262 mAh·g^(-1) at 0.1 A·g^(-1)after 100 cycles),which is much better than that of pure CF electrode(57 mAh·g^(-1) at 0.1 A·g^(-1) after 100 cycles)prepared without the addition of CoP.The rate performance of CoP@CF electrode is also superior to that of pure CF electrode at various current densities from 0.05 to1 A·g^(-1).The sodium storage behavior of CoP@CF was revealed by ex-situ X-ray photoelectron spectroscopy,X-ray diffraction,and synchrotron radiation absorption spectroscopy.This method provides a reference for the design and synthesis of anode materials in sodium-ion batteries.

Phase-controllable cobalt phosphide heterostructure for efficient electrocatalytic hydrogen evolution in water and seawater

Cobalt phosphides attract broad attention as alternatives to platinumbased materials towards hydrogen evolution reaction(HER).The catalytic performance of cobalt phosphides largely depends on the phase structure,but figuring out the optimal phase towards HER remains challenging due to their diverse stoichiometries.In our work,a series of cobalt phosphide nanoparticles with different phase structures but similar particle sizes(CoP-Co_(2)P,Co_(2)P-Co,Co_(2)P,and CoP)on a porous carbon network(PC)were accurately synthesized.The CoP-Co_(2)P/PC heterostructure demonstrates upgraded HER catalytic activity with a low overpotential of 96.7 and 162.1 mV at 10 mA cm−2 in 1 M KOH and 1 M phosphate-buffered saline solution,respectively,with a long-term(120 h)durability.In addition,the CoP-Co_(2)P/PC exhibits good HER performance in alkaline seawater,with a small overpotential of 111.2 mV at 10 mA cm^(−2) and a low Tafel slope of 64.2 mV dec^(−1),as well as promising stability.Density functional theory results show that the Co_(2)P side of the CoP-Co_(2)P/PC heterostructure has the best Gibbs free energy of each step for HER,which contributes to the high HER activity.This study sets the stage for the advancement of high-performance HER electrocatalysts and the implementation of large-scale seawater electrolysis.

Graphene and cobalt phosphide nanowire composite as an anode material for high performance lithium-ion batteries

The synthesis of a composite of cobalt phosphide nanowires and reduced graphene oxide （denoted CoP/RGO） via a facile hydrothermal method combined with a subsequent annealing step is reported. The resulting composite presents large specific surface area and enhanced conductivity, which can effectively facilitate charge transport and accommodates variations in volume during the lithiation/de-lithiation processes. As a result, the CoP/RGO nanocomposite manifests a high reversible specific capacity of 960 mA·h-g-1 over 200 cycles at a current density of 0.2 A·g-1 （297 mA·h·g-1 over 10,000 cycles at a current density of 20 A.g-1） and excellent rate capability （424 mA·h·g-1 at a current density of 10 A·g-1）.

Cobalt phosphide nanoparticles embedded in nitrogendoped carbon nanosheets： Promising anode material with high rate capability and long cycle life for sodiumion batteries

Cobalt phosphide （COP） nanoparticles which were uniformly embedded in N-doped C nanosheets （CNSs） were fabricated via the simple one-step calcination of a Co-based metal-organic framework （MOF） and red P and exhibited a high capacity, fast kinetics, and a long cycle life. This CoP/CNS composite contained small CoP particles （approximately 11.3 nm） and P-C bonds. When its electrochemical properties were evaluated by testing CoP/Na coin cells, the composite delivered a Na-storage capacity of 598 mAh·g-1 at 0.1 A·g-1 according to the total mass of the composite, which means that the capacity of pure CoP reached 831 mAh·g-1 The composite also exhibited a high rate capability and long-term cyclability （174 mAh·g-1 at 20 A·g-1 and 98.5% capacity retention after 900 cycles at 1 A·g-1）, which are commonly attributed to robust P-C bonding and highly conductive CNSs. When the reaction mechanism of the CoP/CNS composite was investigated, a conversion reaction expressed as CoP ＋ 3Na＋ ＋ 3e＋＋ Co ＋ Na3P was observed. The outstanding Na-storage properties of the CoP/CNS composite may suggest a new strategy for developing high-performance anode materials for Na-ion batteries.

Cobalt phosphide nanoarrays with crystalline-amorphous hybrid phase for hydrogen production in universal-pH

To accomplish mass hydrogen production by electrochemical water-splitting,it is a necessary to develop robust,highly active,stable,and cost-effective hydrogen evolution reaction(HER)electrocatalysts that perform comparably to Pt in the universal pH range.In this work,cobalt phosphide hybrid nanosheets supported on carbon felt(CoP HNS/CF)are presented,which exhibit the superior electrocatalytic hydrogen production under a universal-pH.In these nanosheets,a single CoP HNS is composed of polycrystalline CoP and oxygen-enriched amorphous Co-O-P phase.Benefiting from its unique nanoarchitecture,as-fabricated CoP HNS/CF exhibits a tremendous electrocatalytic HER activity and outperforms Pt/C as well as state-of-the-art CoP electrocatalysts in universal-pH.In acidic and neutral media,the CoP HNS/CF shows superior electrocatalytic activity while maintaining its original hybrid crystalline-amorphous phase and morphology.In alkaline medium,the unexpected phase and morphological reorganization of CoP HNS/CF results in outstanding electrocatalytic operation.CoP HNS/CF not only achieves high electrocatalytic activity and kinetics,but also a stable and long operating lifetime even under a high current density of 500 mA cm'2.Furthermore,the fabrication of CoP HNS/CF can be scaled up easily,and the large CoP HNS/CF electrode also exhibits similar electrocatalytic activity and stability.

Conformal and continuous deposition of bifunctional cobalt phosphide layers on p-silicon nanowire arrays for improved solar hydrogen evolution

Vertically aligned p-silicon nanowire （SiNW） arrays have been extensively investigated in recent years as promising photocathodes for solar-driven hydrogen evolution. However, the fabrication of SiNW photocathodes with both high photoelectrocatalytic activity and long-term operational stability using a simple and affordable approach is a challenging task. Herein, we report conformal and continuous deposition of a di-cobalt phosphide （C02P） layer on lithography- patterned highly ordered SiNW arrays via a cost-effective drop-casting method followed by a low-temperature phosphorization treatment. The as-deposited C02P layer consists of crystalline nanoparticles and has an intimate contact with SiNWs, forming a well-defined SiNW@Co2P core/shell nanostructure. The conformal and continuous Co2P layer functions as a highly efficient catalyst capable of substantially improving the photoelectrocatalytic activity for the hydrogen evolution reaction （HER） and effectively passivates the SiNWs to protect them from photo-oxidation, thus prolonging the lifetime of the electrode. As a consequence, the SiNW@Co2P photocathode with an optimized C02P layer thickness exhibits a high photocurrent density of -21.9 mA·cm^-2 at 0 V versus reversible hydrogen electrode and excellent operational stability up to 20 h for solar-driven hydrogen evolution, outperforming many nanostructured silicon photocathodes reported in the literature. The combination of passivation and catalytic functions in a single continuous layer represents a promising strategy for designing high-performance semiconductor photoelectrodes for use in solar-driven water splitting, which may simplify fabrication procedures and potentially reduce production costs.

Recent advances in transition metal phosphide materials:Synthesis and applications in supercapacitors

Supercapacitors(SCs)are considered promising energy storge systems because of their outstanding power density,fast charge and discharge rate and long-term cycling stability.The exploitation of cheap and efficient electrode materials is the key to improve the performance of supercapacitors.As the battery-type materials,transition metal phosphides(TMPs)possess high theoretical specific capacity,good electrical conductivity and superior structural stability,which have been extensively studied to be electrode materials for supercapacitors.In this review,we summarize the up-to-date progress on TMPs materials from diversified synthetic methods,diverse nanostructures and several prominent TMPs and their composites in application of supercapacitors.In the end,we also propose the remaining challenges toward the rational discovery and synthesis of high-performance TMP electrodes materials for energy storage.

Ruthenium nanoclusters anchored on cobalt phosphide hollow microspheres by green phosphating process for full water splitting in acidic electrolyte

Transition metal phosphide(TMP) based electrocatalysts possessing special crystal and electronic structures attract broad attention in the field of electrocatalysis.Immense effort is made to optimize TMP catalysts aiming to satisfy the electrochemical catalysis performance.In this work,an environmentally friendly in situ green phosphating strategy and spatial limiting effect of the RuCo precursor is employed to fabricate the ruthenium nanoclusters anchored on cobalt phosphide hollow microspheres(Ru NCs/Co_(2)P HMs).The obtained Ru NCs/Co_(2)P HMs electrocatalysts exhibit high hydrogen evolution reaction(HER) activity at wide pH ranges,which require an overpotential of 77 mV to achieve the current density of 10 mA/cm^(2) in 0.5 mol/L H_(2)SO_(4) and 118 mV in 1.0 mol/L KOH.Besides,the multifunctional Ru NCs/Co_(2)P HMs exhibit good oxygen evolution reaction(OER) activity with an overpotential of 197 mV to reach the current density of 10 mA/cm^(2) in 0.5 mol/L H_(2)SO_(4),which is below that of the commercial RuO_(2) electrocatalyst(248 mV).A two-electrode electrolyzer is assembled as well,in acid electrolyte,it achieves a current density of 10 mA/cm^(2) at a voltage of 1.53 V,which is superior to that of the benchmark of precious metal-based electrolyzer(1.58 V).

Stable overall water splitting in an asymmetric acid/ alkaline electrolyzer comprising a bipolar membrane sandwiched by bifunctional cobalt-nickel phosphide nanowire electrodes

Water splitting has been proposed to be a promising approach to producing clean hydrogen fuel.The two half-reactions of water splitting,that is,the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),take place kinetically fast in solutions with completely different pH values.Enabling HER and OER to simultaneously occur under kinetically favorable conditions while using exclusively low-cost,earth-abundant electrocatalysts is highly desirable but remains a challenge.Herein,we demonstrate that using a bipolar membrane(BPM)we can accomplish HER in a strongly acidic solution and OER in a strongly basic solution,with bifunctional self-supported cobaltnickel phosphide nanowire electrodes to catalyze both reactions.Such asymmetric acid/alkaline water electrolysis can be achieved at 1.567 V to deliver a current density of 10 mA/cm2 with ca.100%Faradaic efficiency.Moreover,using an“irregular”BPM with unintentional crossover the voltage needed to afford 10 mA/cm2 can be reduced to 0.847 V,due to the assistance of electrochemical neutralization between acid and alkaline.Furthermore,we show that BPM-based asymmetric water electrolysis can be accomplished in a circulated single-cell electrolyzer delivering 10 mA/cm2 at 1.550 V and splitting water very stably for at least 25 hours,and that water electrolysis is enabled by a solar panel operating at 0.908 V(@13 mA/cm2),using an“irregular”BPM.BPMbased asymmetric water electrolysis is a promising alternative to conventional proton and anion exchange membrane water electrolysis.

Integrated strategies on cobalt phosphides-based electrocatalysts for efficient hydrogen evolution reaction

The development of cost-effective and durable hydrogen evolution reaction(HER)electrocatalysts plays a vital role in dealing with the issues related to carbon dioxide emission.Cobalt phosphide-based nanomaterials are evaluated as promising advocates for HER due to high catalytic activities,good stability,and rich defect.This review commences with an exploration of the synthetic pathways of CoP,including solid-phase,solution-phase along with electrochemical methods.Besides,the mechanism of hydrogen formation is expressed thoroughly,after which various integrated strategies of morphology engineering with doping,assisted highly conductive materials,and construction of heterostructure were introduced for HER.Ultimately,burdensome tasks and possible guidance for the advancement of CoP-based nanomaterials were discussed for hydrogen production.

CoP nanoparticles embedded in P and N co-doped carbon as efficient bifunctional electrocatalyst for water splitting

Noble-metal-free hydrogen/oxygen evolution reaction(HER/OER) electrocatalysts, especially bifunctional electrocatalysts, are essential for overall water splitting, but their performance is impeded by many factors like poor electrical conductivity. Herein, we fabricated cobalt phosphide(Co P) nanoparticles embedded in P and N co-doped carbon(PNC) matrix(Co P@PNC) to fully realize the high activity of Co P by maximizing its conductivity. Simply a carbonization coupled phosphidation approach was utilized where Co ions and organic ligands of Co-MOF were transferred into Co P and P and N co-doped carbon. The synthesized material shows an ideal electrical conductivity, excellent HER(overpotential of-84 m V and-120 m V @10 m A cmin acidic and alkaline medias, respectively) and OER(overpotential of 330 m V@10 m A cmin alkaline media) performances. Further, Co P@PNC acts as a superior catalyst for both anode and cathode to catalyze overall water splitting and only requires an voltage of 1.52 V to deliver a current density of 10 m A cm, superior to the noble-metal catalysts system(Pt/C//IrO) and the reported noble-metal-free bifunctional electrocatalysts.

CoxP@NiCo-LDH heteronanosheet arrays as efficient bifunctional electrocatalysts for co-generation of value-added formate and hydrogen with less-energy consumption

The inefficiency of water splitting is mainly due to the sluggish anodic water oxidation reaction. Replacing water oxidation with thermodynamically more favorable selective methanol oxidation reaction and developing robust bifunctional electrocatalysts are of great significance. Herein, a hierarchical heteronanostructure with Ni–Co layered double hydroxide(LDH) ultrathin nanosheets coated on cobalt phosphide nanosheets arrays(CoxP@NiCo-LDH) are fabricated and used for co-electrolysis of methanol/water to co-produce value-added formate and hydrogen with saving energy. Benefiting from the fast charge transfer introduced by phosphide nanoarrays, the synergy in nanosheets catalysts with hetero-interface,CoxP@NiCo-LDH/Ni foam(NF) exhibits superior electrocatalytic performance(10 mA cm-2@ 1.24 V and-0.10 V for methanol selective oxidation and hydrogen evolution reaction, respectively). Furthermore,CoxP@NiCo-LDH/NF-based symmetric two-electrode electrolyzer drives a current density of 10 m A cm-2 with a low cell voltage of only 1.43 V and the Faradaic efficiency towards the generation of formate and H2 are close to 100% in the tested range of current density(from 40 to 200 m A cm-2). This work highlights the positive effect of hetero-interaction in the design of more efficient eletrocatalysts and might guide the way towards facile upgrading of alcohols and energy-saving electrolytic H2 co-generation.

Anchoring nitrogen-doped Co_(2)P nanoflakes on NiCo_(2)O_(4)nanorod arrays over nickel foam as high-performance 3D electrode for alkaline hydrogen evolution

Effective and robust electrocatalysts are mainly based on innovative materials and unique structures.Herein,we designed a flakelike cobalt phosphide-based catalyst supporting on NiCo_(2)O_(4)nanorods array,which in-situ grew on the nickel foam(NF)current collector,referring as NCo_(2)P/NiCo_(2)O_(4)/NF electrode.By optimizing the microstructure and electronic structure through 3D hierarchy fabrication and nitrogen doping,the catalyst features with abundant electrochemical surface area,favorable surface wettability,excellent electron transport,as well as tailored d band center.Consequently,the as-prepared N-Co_(2)P/NiCo_(2)O_(4)/NF electrode exhibits an impressive HER activity with a low overpotentials of58 mV at 10 mA cm^(-2),a Tafel slop of 75 mV dec^(-1),as well as superior durability in alkaline medium.This work may provide a new pathway to effectively improve the hydrogen evolution performance of transition metal phosphides and to develop promising electrodes for practical electrocatalysis.

3D ordered mesoporous cobalt ferrite phosphides for overall water splitting

Developing low-cost and earth-abundant electrocatalysts with high performance for electrochemical water splitting is a challenging issue. Herein, we report a facile and effective way to fabricate three-dimension(3D) ordered mesoporous Co1-xFexP(x=0, 0.25, 0.5, 0.75) electrocatalyst.Benefiting from 3D ordered mesoporous pore channels and composition optimization, the Co0.75Fe0.25 P exhibits excellent electrocatalytic activities with low overpotentials of 270 and 209 mV at 10 mA cm^-2 for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER), respectively, in the alkaline electrolyte along with a durable electrochemical stability. In addition, as both the cathode and anode, the Co0.75Fe0.25P also exhibits superior electrolysis water splitting performance with only an applied voltage of 1.63 V to attain a current density of 10 m A cm^-2 without obvious decay for 18 h,indicating that the Co0.75Fe0.25P is an efficient electrocatalyst for overall water splitting.

Cobalt tungsten phosphide with tunable W-doping as highly efficient electrocatalysts for hydrogen evolution reaction

It has been of interest in seeking electrocatalysts that could exercise equally high-efficient and durable hydrogen evolution upon nonselective electrolytes in both acidic and alkaline environments. Herein, we report a facile strategy to fabricate cobalt tungsten phosphides (CoxW2−xP2/C) hollow polyhedrons with tunable composition based on metal-organic frameworks (MOFs) template method. By the deliberate control of W doping, the synthesized catalyst with the composition of Co0.9W1.1P2/C is found to be able to achieve a current density of 10 mA·cm^(−2) at overpotentials of 35 and 54 mV in acidic and alkaline media, respectively. This combined electrochemical property stands atop the state-of-the-art electrocatalyst counterparts. To unveil the peculiar behavior of the structure, density functional theory (DFT) calculation was implemented and reveals that the surface W-doping facilitates the optimization of hydrogen absorption free energy (ΔGH*) as well as the thermodynamic and kinetics barriers for water dissociation, which is coupled with the hollow structure of Co-W phosphides, leading to the prominent HER catalytic performance.