A highly active and stable hydrogen evolution catalyst based on pyrite-structured cobalt phosphosulfide

Regulating the electronic structure of CoMoO4 microrod by phosphorus doping: an efficient electrocatalyst for the hydrogen evolution reaction

It is of extreme importance to design efficient electrocatalysts for hydrogen evolution reaction (HER), which is considered as a promising approach to provide efficient and renewable clean fuel (hydrogen). Tuning the electronic structure through heteroatom doping demonstrates one of the most effective strategies to promote the electrocatalytic performance of HER. Herein, phosphorus-doping modulation is utilized to fabricate monoclinic P-CoMoO₄ with optimized electron structure supported on nickel foam (P-CoMoO₄/NF) for alkaline HER via a facile hydrothermal method, followed by low-temperature phosphidation. Notably, P-CoMoO₄/NF shows outstanding electrocatalytic performance for HER in 1 M KOH with a low overpotential of 89 mV at 10 mA cm^-2, a remarkable Tafel slope value of 59 mV dec^-1, and excellent 24 h-long stability. The excellent catalyst activity and stability merits of P-CoMoO₄/NF are comparable to the reported highly efficient non-precious metal HER electrocatalysts and could be applied as a powerful electrocatalyst in water electrolysis. This work provides a superior synthesis strategy for the effective design and rational fabrication of low-cost, highly active, and highly stable non-precious metal HER electrocatalysts for electricity-to-hydrogen applications.

Highly Crystalline Hollow Toroidal Copper Phosphosulfide via Anion Exchange: A Versatile Cation Exchange Nanoplatform

Postmodification of nanocrystals through cation exchange has been very successful in diversifying nanomaterial compositions while retaining the structural motif. Copper compound nanoparticles are particularly useful as templates because of inherent defects serving as effective cation diffusion routes and excellent cation mobility. Therefore, the development of shape-controlled multianion systems, such as copper phosphosulfide, can potentially lead to the formation of diverse metal phosphosulfide nanomaterials that have otherwise inaccessible compositions and structures. However, there is, to the best of our knowledge, no report on the shape-controlled synthesis of copper phosphosulfide nanoparticles because the introduction of the second anion to the metal compound might destroy the nanoparticle morphology and crystallinity due to the required high energy for anion diffusion and mixing. Herein, we report that it is feasible to transfer the structural motif of copper sulfide to copper phosphosulfide using tris(diethylamino)phosphine. The anion-mixed copper phosphosulfide in the form of a hollow toroid could provide a pathway to previously inaccessible phases and morphologies. We verified the versatility of a copper phosphosulfide hollow toroid as a cation-exchange template by the successful synthesis of cobalt, nickel, indium, and cadmium phosphosulfides as well as bimetallic cobalt-nickel phosphosulfide (Co_2-xNi_xP_1-yS_y) with a retained structural motif.

Integration of bio-inspired lanthanide-transition metal cluster and P-doped carbon nitride for efficient photocatalytic overall water splitting

Photosynthesis in nature uses the Mn₄CaO₅ cluster as the oxygen-evolving center to catalyze the water oxidation efficiently in photosystem II. Herein, we demonstrate bio-inspired heterometallic LnCo₃ (Ln = Nd, Eu and Ce) clusters, which can be viewed as synthetic analogs of the CaMn₄O₅ cluster. Anchoring LnCo₃ on phosphorus-doped graphitic carbon nitrides (PCN) shows efficient overall water splitting without any sacrificial reagents. The NdCo₃/PCN-c photocatalyst exhibits excellent water splitting activity and a quantum efficiency of 2.0% at 350 nm. Ultrafast transient absorption spectroscopy revealed the transfer of a photoexcited electron and hole into the PCN and LnCo₃ for hydrogen and oxygen evolution reactions, respectively. A density functional theory (DFT) calculation showed the cooperative water activation on lanthanide and O−O bond formation on transition metal for water oxidation. This work not only prepares a synthetic model of a bio-inspired oxygen-evolving center but also provides an effective strategy to realize light-driven overall water splitting.

Metal Foam Electrode as a Cathode for Copper Electrowinning

The geometry of porous materials is complex, and the determination of the true surface area is important because it affects current density, how certain reactions will progress, their rates, etc. In this work, we have investigated the dependence of the electrochemical deposition of copper coatings on the geometry of the copper substrate (flat plates or 3D foams). Chronoamperometric measurements show that copper deposition occurs 3 times faster on copper foams than on a flat electrode with the same geometric area in the same potential range, making metal foams great electrodes for electrowinning. Using electrochemical impedance spectroscopy (EIS), the mechanism of copper deposition was determined at various concentrations and potentials, and the capacities of the double electric layer (DL) for both types of electrodes were calculated. The DL capacity on the foam electrodes is up to 14 times higher than that on the plates. From EIS data, it was determined that the charge transfer resistance on the Cu foam electrode is 1.5–1.7 times lower than that on the Cu plate electrode. Therefore, metal foam electrodes are great candidates to be used for processes that are controlled by activation polarization or by the adsorption of intermediate compounds (heterogeneous catalysis) and processes occurring on the entire surface of the electrode.

Insights into N, P, S multi-doped Mo2C/C composites as highly efficient hydrogen evolution reaction catalysts

Heteroatom doping has been proved to be an effective strategy to optimize the activity of hydrogen evolution reaction (HER) catalysts. Herein, we report N, P, S multi-doped Mo2C/C composites exhibiting highly efficient HER performance in acidic solution, which are facilely fabricated via annealing of N, P, S-containing MoO x -polyaniline (MoO x -PANI) hybrid precursors. The optimized N, P, S multi-doped Mo2C/C catalyst with a moderate P dopant level (NPS-Mo2C/C-0.5) exhibits excellent performance with an overpotential of 53 mV to achieve a current density of 20 mA cm-2, a Tafel slope of 72 mV dec-1 and good stability in acidic electrolytes. Based on the study of XPS, EPR and 31P MAS NMR, the excellent electrocatalytic performance could be attributed to the effective electronic configuration modulation of both Mo2C nanorods and the carbon matrix, derived from stronger synergistic N, P, S multi-doping coupling effects. This work provides a promising methodology for the design and fabrication of multi-doped transition metal based electrocatalysts via electronic structure engineering.

Transition-Metal Phosphorus Trisulfides and its Vacancy Defects: Emergence of a New Class of Anode Material for Li-Ion Batteries

In the search of suitable anode candidates with high specific capacity, favorable potential, and structural stability for lithium-ion batteries (LIBs), transition-metal phosphorus trisulfides (TMPS3 ) can be considered as one of the most promising alternatives to commercial graphite. Here, it was demonstrated that the limitations of commercial anode materials (i.e., low specific capacity, large volume change, and high lithium diffusion barrier as well as nucleation) can be circumvented by using TMPS3 monolayer surfaces. The study revealed that lithium binds strongly to TMPS3 monolayers (-2.31 eV) without any distortion of the surface, with Li@TMPS3 exhibiting enhanced stability compared with other 2D analogues (graphene, phosphorene, MXenes, transition-metal sulfides and phosphides). The binding energy of lithium was overwhelmingly enhanced with vacancy defects. The vacancy-mediated TMPS3 surfaces showed further amplification of Li binding energy from -2.03 to -2.32 eV and theoretical specific capacity of 441.65 to 484.34 mAh g-1 for MnPS3 surface. Most importantly, minimal change in volume (less than 2 %) after lithiation makes TMPS3 monolayers a very effective candidate for LIBs. Additionally, the ultralow lithium diffusion barrier (0.08 eV) compared with other existing commercial anode material proves the superiority of TMPS3 .

Effective accommodation and conversion of polysulfides using organic-inorganic hybrid frameworks for long-life lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are one of the most promising candidates for meeting the emerging market demands for energy storage, and have the advantages including high energy density and low cost. However, the practical application of Li-S batteries is hindered by the lithium polysulfide (LiPS) shuttle, which induces low sulfur utilization and unsatisfactory capacity retention. To address this problem, recent studies have focused on improving the transformation of LiPS into insoluble Li2S2/Li2S through methods beyond physical or chemical adsorption. Nevertheless, the commonly used host materials have limited ability to simultaneously trap and propel redox transfer of LiPS. Herein, the bottom-up construction of new organic-inorganic hybrid frameworks for sulfur cathodes is proposed to fundamentally restrict LiPS dissolution and enhance their electrochemical transformation. The synergistic integration of organic cellulose networks and inorganic ZIF-derivatives caused highly efficient LiPS mediators to suppress the shuttle effect and retain electrode stability. The resulting RCE-Co3O4@G-S cathode materials delivered a stable capacity of 726.5 mA h g-1 at 0.2 C after 350 cycles, with a very low fading rate of 0.026% per cycle and a high coulombic efficiency of 98.9%.

Atomically Engineered Transition Metal Dichalcogenides for Liquid Polysulfide Adsorption and Their Effective Conversion in Li-S Batteries

Curtailing the polysulfide shuttle by anchoring the intermediate lithium polysulfides (LiPS) within the electrode structure is essential to impede the rapid capacity fade in lithium-sulfur (Li-S) batteries. While most of the contemporary Li-S cathode surfaces are capable of entrapping certain LiPS, developing a unique electrode material that can adsorb all the intermediates of sulfur redox is imperative. Herein, we report doping of the MoS₂ atomic structure with nickel (Ni@1TMoS₂) to modulate its absorption capability toward all LiPS and function as an electrocatalyst for Li-S redox. Detailed in situ and ex situ spectroscopic analysis revealed that both Ni and Mo sites chemically anchor all the intermediate of LiPS. Electrochemical studies and detailed kinetics analysis suggested that the conversion of liquid LiPS to solid end products are facilitated on the Ni@1TMoS₂ electrocatalytic surface. Further, the employment of the Ni@1TMoS₂ electrocatalyst enhances the Li⁺ diffusion coefficient, thus contributing to the realization of a high capacity of 1107 mA h g^-1 at 0.2C with a very limited capacity fade of 0.19% per cycle for over 100 cycles. In addition, this cathode demonstrated an excellent high rate and long cycling performance for over 300 cycles at a 1C rate.

Synergistic Modulation of Non-Precious-Metal Electrocatalysts for Advanced Water Splitting

ConspectusHydrogen is an ideal energy carrier and plays a critical role in the future energy transition. Distinct from steam reforming, electrochemical water splitting, especially powered by renewables, has been considered as a promising technique for scalable production of high-purity hydrogen with no carbon emission. Its commercialization relies on the reduction of electricity consumption and thus hydrogen cost, calling for highly efficient and cost-effective electrocatalysts with the capability of steadily working at high hydrogen output. This requires the electrocatalysts to feature (1) highly active intrinsic sites, (2) abundant accessible active sites, (3) effective electron and mass transfer, (4) high chemical and structural durability, and (5) low-cost and scalable synthesis. It should be noted that all these requirements should be fulfilled together for a practicable electrocatalyst. Much effort has been devoted to addressing one or a few aspects, especially improving the electrocatalytic activity by electronic modulation of active sites, while few reviews have focused on the synergistic modulation of these aspects together although it is essential for advanced electrochemical water splitting.In this Account, we will present recent innovative strategies with an emphasis on our solutions for synergistically modulating intrinsic active sites, electron transportation, mass transfer, and gas evolution, as well as mechanical and chemical durability, of non-precious-metal electrocatalysts, aiming for cost-effective and highly efficient water splitting. The following approaches for coupling these aspects are summarized for both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). (1) Synergistic electronic modulations. The electronic structure of a catalytic site determines the adsorption/desorption of reactive intermediates and thus intrinsic activity. It can be tuned by heterogeneous doping, strain effect, spin polarization, etc. Coupling these effects to optimize the reaction pathways or target simultaneously the activity and stability would advance electrocatalytic performance. (2) Synergistic electronic and crystalline modulation. The crystallinity, crystalline phase, crystalline facets, crystalline defects, etc. affect both activity and stability. Coupling these effects with electronic modulation would enhance the activity together with stability. (3) Synergistic electronic and morphological modulation. It will focus on concurrently modulating electronic structure for improving the intrinsic activity and morphology for increasing accessible active sites, especially through single action or processing. The mass transfer and gas evolution properties can also be enhanced by morphological modulation to enable water splitting at large output. (4) Synergistic modulation of elementary reactions. Electrocatalytic reaction generally consists of a couple of elementary reactions. Each one may need a specific active site. Designing and combining various components targeting every elementary step on a space-limited catalyst surface will balance the intermediates and these steps for accelerating the overall reaction. (5) Integrated electrocatalyst design. Taking all these strategies together into account is necessary to integrate all above essential features into one electrocatalyst for enabling high-output water electrolysis. Beyond the progress made to date, the remaining challenges and opportunities is also discussed. With these insights, hopefully, this Account will shed light on the rational design of practical water-splitting electrocatalysts for the cost-effective and scalable production of hydrogen.

Investigating affordable cobalt based metallosurfactant as an efficient electrocatalyst for hydrogen evolution reaction

The implementation of hydrogen evolution reaction (HER) is an essential requirement of a stable electrocatalyst that competes for the performance of noble metals (Pt, Pd), especially in acidic conditions. This research reports the design and development of affordable cobalt (Co) based metallosurfactant (CoCPC(I)) which performs under acidic medium (0.5 N H₂SO₄) for HER. Such a fabricated catalyst is able to lower the cathodic potentials efficiently and exhibits 130 mV onset potential and Tafel slope of 104 mVdec^-1 that depicts the presence of Volmer-Heyrovsky mechanism. The results of the studies confirm that our synthesized metallosurfactant forms metallomicelles on the surface of electrode and surface remains stable even after the electrochemical cycle. Further, the surfactant protects the metal centre as an active site for a longer time via forming metallo-micelles which helps to sustain activity. These outcomes reveal the efficient mass and charge transfer capability of CoCPC(I) which results in faster charge transfer kinetics. Therefore, the utilization of Co based metallosurfactant can split water easily, cost-effectively, and without using hazardous chemicals. Our demonstrated technology seems suitable for industrial applications due to features of large-scale production possibilities.

Well-defined CoSe2@MoSe2 hollow heterostructured nanocubes with enhanced dissociation kinetics for overall water splitting

Hollow heterostructures have tremendous advantages in electrochemical energy storage and conversion areas due to their unique structure and composition characteristics. Here, we report the controlled synthesis of hollow CoSe₂ nanocubes decorated with ultrathin MoSe₂ nanosheets (CoSe₂@MoSe₂) as an efficient and robust bifunctional electrocatalyst for overall water splitting in a wide pH range. It is found that integrating ultrathin MoS₂ nanosheets with hollow CoSe₂ nanocubes can provide abundant active sites, promote electron/mass transfer and bubble release and facilitate the migration of charge carriers. Additionally, the surface electron coupling in the heterostructures enables it to serve as a source of sites for H⁺ and/or OH^- adsorption, thus reducing the activation barrier for water molecules adsorption and dissociation. As a result, the title compound, CoSe₂@MoSe₂ hollow heterostructures, exhibits an overpotential of 183 mV and 309 mV at a current density of 10 mA cm^-2 toward hydrogen evolution reactions and oxygen evolution reactions in 1.0 M KOH, respectively. When applied as both cathode and anode for overall water splitting, a low battery voltage of 1.524 V is achieved along with excellent stability for at least 12 h. This work provides a new idea for the design and synthesis of high-performance catalysts for electrochemical energy storage and conversion.

General Strategy to Optimize Gas Evolution Reaction via Assembled Striped-Pattern Superlattices

Redesigning heterogeneous catalysts so that they can simultaneously integrate the efficiency and durability under reaction environments with respect to gas fuel production, such as hydrogen (H₂), oxygen (O₂), or carbon monoxide (CO), has proven challenging. In this work, we report the successful template-assisted printing-based assembly of platinum (Pt) nanoparticles (NPs) into striped-pattern (SP) superlattices to produce H₂. In comparison to drop-casting flat Pt NPs films, SP superlattices lead to higher mass transference and smaller bubble stretch force, representing a general strategy to improve the efficiency and durability of pre-existed Pt catalysts for the hydrogen evolution reaction (HER), as well as higher current densities than commercial Pt/C, Pt NP films, and many of the other Pt-based or non-Pt-based HER catalysts reported in the literature. The generic nature of template-assisted printing leads to flexibility in the composition, size, and shape of the constituent NPs or molecules, and thus extends such an accelerated technique for producing the oxygen evolution reaction and electrochemical reduction of CO₂ to CO.

Voltage issue of aqueous rechargeable metal-ion batteries

Over the past two decades, a series of aqueous rechargeable metal-ion batteries (ARMBs) have been developed, aiming at improving safety, environmental friendliness and cost-efficiency in fields of consumer electronics, electric vehicles and grid-scale energy storage. However, the notable gap between ARMBs and their organic counterparts in energy density directly hinders their practical applications, making it difficult to replace current widely-used organic lithium-ion batteries. Basically, this huge gap in energy density originates from cell voltage, as the narrow electrochemical stability window of aqueous electrolytes substantially confines the choice of electrode materials. This review highlights various ARMBs with focuses on their voltage characteristics and strategies that can effectively raise battery voltage. It begins with the discussion on the fundamental factor that limits the voltage of ARMBs, i.e., electrochemical stability window of aqueous electrolytes, which decides the maximum-allowed potential difference between cathode and anode. The following section introduces various ARMB systems and compares their voltage characteristics in midpoint voltage and plateau voltage, in relation to respective electrode materials. Subsequently, various strategies paving the way to high-voltage ARMBs are summarized, with corresponding advancements highlighted. The final section presents potential directions for further improvements and future perspectives of this thriving field.

Enhancing photoelectrochemical performance of ZnIn2S4 by phosphorus doping for sensitive detection of miRNA-155

The photoelectrochemical performance of ZnIn₂S₄ was enhanced by P doping for the sensitive detection of the cancer biomarker microRNA-155.

PtMn/PtCo alloy nanofascicles: robust electrocatalysts for electrocatalytic hydrogen evolution reaction under both acidic and alkaline conditions

Herein, PtMn and PtCo nanofascicles were prepared by ultrathin nanofibers using a versatile method, and can be employed as effective electrocatalysts toward the HER under both acidic and alkaline conditions.

Ordered porous Ni in situ decorated by thin-layer amorphous nickel–phosphorus via mild electrochemical-phosphorization for enhancing the hydrogen evolution performance

Ni–P/p-Ni with a rich Ni–P/Ni interface region was constructed for enhancing the HER through a facile and ecofriendly electrochemical-phosphorization process.

Inserting Co and P into MoS2 photocathodes: enhancing hydrogen evolution reaction catalytic performance by activating edges and basal planes with sulfur vacancies

The production of hydrogen using solar energy via a photoelectrochemical system is an effective technique for meeting present clean energy needs.

N-induced lattice contraction generally boosts the hydrogen evolution catalysis of P-rich metal phosphides

P-rich transition metal phosphides (TMPs) with abundant P sites have been predicted to be more favorable for hydrogen evolution reaction (HER) catalysis. However, the actual activities of P-rich TMPs do not behave as expected, and the underlying essence especially at the atomic level is also ambiguous. Our structural analysis reveals the inferior activity could stem from the reduced overlap of atomic wave functions between metal and P with the increase in P contents, which consequently results in too strong P-H interaction. To this end, we used N-induced lattice contraction to generally boost the HER catalysis of P-rich TMPs including CoP2, FeP2, NiP2, and MoP2. Refined structural characterization and theoretical analysis indicate the N-P strong interaction could increase the atomic wave function overlap and eventually modulate the H adsorption strength. The concept of lattice engineering offers a new vision for tuning the catalytic activities of P-rich TMPs and beyond.

Improving catalysis for electrochemical water splitting using a phosphosulphide surface

A yolk–shell-structured porous phosphosulphide catalyst exhibits superior activities towards the hydrogen and oxygen evolution reactions in water splitting in an alkaline electrolyte.

P-doped nickel sulfide nanosheet arrays for alkaline overall water splitting

Heazlewoodite, Ni₃S₂, is one of the most promising bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media due to its metallic conductivity and low cost.

CoSe2 nanobelt coupled with CoMoO4 nanosheet as efficient electrocatalysts for hydrogen and oxygen evolution reaction

Designing non-noble electrocatalysts with low-cost and efficient is crucial to the development of sustainable and clean energy resources. Here, we synthesized a novel S–CoSe2/CoMoO4 and O–CoSe2/CoMoO4hybrid electrocatalysts for the HER and OER, respectively. Possibly due to the synergetic chemical coupling effects between CoSe2/DETA and CoMoO4, and the introduction of S heteroatom and oxygen vacancy, this hybrid could expose enough active edges, and then promoted the constructed hybrid displayed superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic performance. The S–CoSe2/CoMoO4 sample afforded a current density of 10 ​mAcm-2 at a small overpotential of 177 ​mV and a small Tafel slope of 54 ​mV dec−1. Moreover, the oxidized CoSe2/CoMoO4 (O–CoSe2/CoMoO4) also displayed a remarkable catalytic property for OER with a small Tafel slope of 43 ​mV dec−1, as well as excellent stability in 1.0 ​M KOH. Therefore, this noble-metal-free and highly efficient catalyst enables prospective applications for electrochemical applications.

•The novel S-CoSe2/CoMoO4 and O-CoSe2/CoMoO4 hybrid electrocatalysts are reported. •The oxygen vacancy resulted in O-CoSe2/CoMoO4 displayed excellent stability for OER. •This non-noble based electrocatalysts are valuable for the future clean energy.

Polymorphic cobalt diselenide as extremely stable electrocatalyst in acidic media via a phase-mixing strategy

Many platinum group metal-free inorganic catalysts have demonstrated high intrinsic activity for diverse important electrode reactions, but their practical use often suffers from undesirable structural degradation and hence poor stability, especially in acidic media. We report here an alkali-heating synthesis to achieve phase-mixed cobalt diselenide material with nearly homogeneous distribution of cubic and orthorhombic phases. Using water electroreduction as a model reaction, we observe that the phase-mixed cobalt diselenide reaches the current density of 10 milliamperes per square centimeter at overpotential of mere 124 millivolts in acidic electrolyte. The catalyst shows no sign of deactivation after more than 400 h of continuous operation and the polarization curve is well retained after 50,000 potential cycles. Experimental and computational investigations uncover a boosted covalency between Co and Se atoms resulting from the phase mixture, which substantially enhances the lattice robustness and thereby the material stability. The findings provide promising design strategy for long-lived catalysts in acid through crystal phase engineering.

Noble-metal-free catalysts often show stability issues in acidic media due to structural degradation. Here authors show that phase-mixed engineering of cobalt diselenide electrocatalysts can enable greater covalency of Co-Se bonds and improve robustness for catalyzing hydrogen evolution in acid.

Superb water splitting activity of the electrocatalyst Fe3Co(PO4)4 designed with computation aid

For efficient water splitting, it is essential to develop inexpensive and super-efficient electrocatalysts for the oxygen evolution reaction (OER). Herein, we report a phosphate-based electrocatalyst [Fe₃Co(PO₄)₄@reduced-graphene-oxide(rGO)] showing outstanding OER performance (much higher than state-of-the-art Ir/C catalysts), the design of which was aided by first-principles calculations. This electrocatalyst displays low overpotential (237 mV at high current density 100 mA cm⁻² in 1 M KOH), high turnover frequency (TOF: 0.54 s⁻¹), high Faradaic efficiency (98%), and long-term durability. Its remarkable performance is ascribed to the optimal free energy for OER at Fe sites and efficient mass/charge transfer. When a Fe₃Co(PO₄)₄@rGO anodic electrode is integrated with a Pt/C cathodic electrode, the electrolyzer requires only 1.45 V to achieve 10 mA cm⁻² for whole water splitting in 1 M KOH (1.39 V in 6 M KOH), which is much smaller than commercial Ir-C//Pt-C electrocatalysts. This cost-effective powerful oxygen production material with carbon-supporting substrates offers great promise for water splitting.

The sluggish kinetics of the oxygen evolution reaction (OER) is the main obstacle in water splitting which is generally catalyzed by precious metals. Here, authors report a DFT predicted non-precious bimetallic phosphate electrocatalyst that displays high OER activity and stability.

A General Method for the Synthesis of Hybrid Nanostructures Using MoSe2 Nanosheet-Assembled Nanospheres as Templates

The layered transition metal dichalcogenides (TMDs) and transition metal phosphides are low-cost, earth-abundant, and robust electrocatalysts for hydrogen evolution reaction (HER). Integrating them into hybrid nanostructures is potentially promising to further boost the catalytic activity toward HER based on their synergistic effects. Herein, we report a general method for the synthesis of a series of MoSe₂-based hybrid nanostructures, including MoSe₂-Ni₂P, MoSe₂-Co₂P, MoSe₂-Ni, MoSe₂-Co, and MoSe₂-NiS, by postgrowth of Ni₂P, Co₂P, Ni, Co, and NiS nanostructures on the presynthesized MoSe₂ nanosheet-assembled nanospheres, respectively, via a colloidal synthesis method. As a proof-of-concept application, the as-synthesized hybrid nanostructures are used as electrocatalysts for HER, exhibiting high activity and stability in acidic media. Among them, the MoSe₂-Co₂P composite shows the highest HER activity with an overpotential of 167 mV at 10 mA cm^-2.

Phosphorus Incorporation into Co9 S8 Nanocages for Highly Efficient Oxygen Evolution Catalysis

The improvement of activity of electrocatalysts lies in the increment of the density of active sites or the enhancement of intrinsic activity of each active site. A common strategy to realize dual active sites is the use of bimetal compound catalysts, where each metal atom contributes one active site. In this work, a new concept is presented to realize dual active sites with tunable electron densities in monometal compound catalysts. Dual Co²⁺ tetrahedral (Co²⁺ (T_d )) and Co³⁺ octahedral (Co³⁺ (O_h )) coordination active sites are developed and adjustable electron densities on the Co²⁺ (T_d ) and Co³⁺ (O_h ) are further achieved by phosphorus incorporation (P-Co₉ S₈ ). The experimental results and density functional theory calculations show that the nonmetal P doping can systematically modulate charge density of Co²⁺ (T_d ) and Co³⁺ (O_h ) in P-Co₉ S₈ and simultaneously improve the electrical conductivity of Co₉ S₈ , which substantially enhances oxygen evolution reaction performance of P-Co₉ S₈ .

P-Doped Iron-Nickel Sulfide Nanosheet Arrays for Highly Efficient Overall Water Splitting

Iron-nickel sulfide ((Ni,Fe)₃S₂) is one of the most promising bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media because of their metallic conductivity and low cost. However, the reported HER activity of (Ni,Fe)₃S₂ is still unsatisfactory. Herein, three-dimensional self-supported phosphorus-doped (Ni,Fe)₃S₂ nanosheet arrays on Ni foam (P-(Ni,Fe)₃S₂/NF) are synthesized by a simple one-step simultaneous phosphorization and sulfuration route, which exhibits dramatically enhanced HER activity as well as drives remarkable OER activity. The incorporation of P significantly optimized the hydrogen/water absorption free energy (ΔG_H*/ΔG_H2O*), enhanced electrical conductivity, and increased electrochemical surface area. Accordingly, the optimal P-(Ni,Fe)₃S₂/NF exhibits relatively low overpotentials of 98 and 196 mV at 10 mA cm^-2 for HER and OER in 1 M KOH, respectively. Furthermore, an alkaline electrolyzer comprising the P-(Ni,Fe)₃S₂/NF electrodes needs a very low cell voltage of 1.54 V at 10 mA cm^-2 and exhibits long-term stability and outperforms most other state-of-the-art electrocatalysts. The reported electrocatalyst activation approach by anion doping can be adapted for other transition-metal chalcogenides for water electrolysis, offering great promise for future applications.

Self-Supported and Flexible Sulfur Cathode Enabled via Synergistic Confinement for High-Energy-Density Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have attracted much attention in the field of electrochemical energy storage due to their high energy density and low cost. However, the "shuttle effect" of the sulfur cathode, resulting in poor cyclic performance, is a big barrier for the development of Li-S batteries. Herein, a novel sulfur cathode integrating sulfur, flexible carbon cloth, and metal-organic framework (MOF)-derived N-doped carbon nanoarrays with embedded CoP (CC@CoP/C) is designed. These unique flexible nanoarrays with embedded polar CoP nanoparticles not only offer enough voids for volume expansion to maintain the structural stability during the electrochemical process, but also promote the physical encapsulation and chemical entrapment of all sulfur species. Such designed CC@CoP/C cathodes with synergistic confinement (physical adsorption and chemical interactions) for soluble intermediate lithium polysulfides possess high sulfur loadings (as high as 4.17 mg cm^-2 ) and exhibit large specific capacities at different C-rates. Specially, an outstanding long-term cycling performance can be reached. For example, an ultralow decay of 0.016% per cycle during the whole 600 cycles at a high current density of 2C is displayed. The current work provides a promising design strategy for high-energy-density Li-S batteries.

Immobilized Single Molecular Molybdenum Disulfide on Carbonized Polyacrylonitrile for Hydrogen Evolution Reaction

Designing a MoS₂ catalyst having a large number of active sites and high site activity enables the catalytic activity toward the hydrogen evolution reaction to be improved. Herein, we report the synthesis of a low-cost and catalytically active immobilized single molecular molybdenum disulfide on carbonized polyacrylonitrile (MoS₂-cPAN) electrocatalyst. From the extended X-ray absorption fine structure spectra analysis, we found that the as-prepared material has no metal-metal scattering and it resembles MoS₂ with a molecular state. Meanwhile, the size of the molecular MoS₂ has been estimated to be about 1.31 nm by high-angle annular dark-field scanning transmission electron microscopy. A low coordination number and maximum utilization of the single molecular MoS₂ surface enable MoS₂-cPAN to demonstrate electrochemical performance significantly better than that of bulk MoS₂ by two orders of exchange current density ( j_o) and turnover frequency to the hydrogen evolution.

Phosphorus-Rich Colloidal Cobalt Diphosphide (CoP2 ) Nanocrystals for Electrochemical and Photoelectrochemical Hydrogen Evolution

Developing earth-abundant and efficient electrocatalysts for photoelectrochemical water splitting is critical to realizing a high-performance solar-to-hydrogen energy conversion process. Herein, phosphorus-rich colloidal cobalt diphosphide nanocrystals (CoP₂ NCs) are synthesized via hot injection. The CoP₂ NCs show a Pt-like hydrogen evolution reaction (HER) electrocatalytic activity in acidic solution with a small overpotential of 39 mV to achieve -10 mA cm^-2 and a very low Tafel slope of 32 mV dec^-1 . Density functional theory (DFT) calculations reveal that the high P content both physically separates Co atoms to prevent H from over binding to multiple Co atoms, while simultaneously stabilizing H adsorbed to single Co atoms. The catalytic performance of the CoP₂ NCs is further demonstrated in a metal-insulator-semiconductor photoelectrochemical device consisting of bottom p-Si light absorber, atomic layer deposition Al-ZnO passivation layers, and the CoP₂ cocatalyst. The p-Si/AZO/TiO₂ /CoP₂ photocathode shows a photocurrent density of -16.7 mA cm^-2 at 0 V versus reversible hydrogen electrode (RHE) and an output photovoltage of 0.54 V. The high performance and stability are attributed to the junction between p-Si and AZO, the corrosion-resistance of the pinhole-free TiO₂ protective layer, and the fast HER kinetics of the CoP₂ NCs.

Unveiling the Interfacial Effects for Enhanced Hydrogen Evolution Reaction on MoS2 /WTe2 Hybrid Structures

Using the MoS₂ -WTe₂ heterostructure as a model system combined with electrochemical microreactors and density function theory calculations, it is shown that heterostructured contacts enhance the hydrogen evolution reaction (HER) activity of monolayer MoS₂ . Two possible mechanisms are suggested to explain this enhancement: efficient charge injection through large-area heterojunctions between MoS₂ and WTe₂ and effective screening of mirror charges due to the semimetallic nature of WTe₂ . The dielectric screening effect is proven minor, probed by measuring the HER activity of monolayer MoS₂ on various support substrates with dielectric constants ranging from 4 to 300. Thus, the enhanced HER is attributed to the increased charge injection into MoS₂ through large-area heterojunctions. Based on this understanding, a MoS₂ /WTe₂ hybrid catalyst is fabricated with an HER overpotential of -140 mV at 10 mA cm^-2 , a Tafel slope of 40 mV dec^-1 , and long stability. These results demonstrate the importance of interfacial design in transition metal dichalcogenide HER catalysts. The microreactor platform presents an unambiguous approach to probe interfacial effects in various electrocatalytic reactions.

Interfacial engineering of cobalt sulfide/graphene hybrids for highly efficient ammonia electrosynthesis

Ammonia is one of the most important chemical raw materials with an annual production exceeding 200 million tons. The Haber–Bosch process is still the dominant route for industrial ammonia synthesis, which consumes 1∼3% of global annual energy production and represents a significant contributor to climate change. Electrocatalytic N₂ reduction reaction is an attractive alternative candidate for carbon-free and sustainable NH₃ production, but often suffers from low efficiency. Here, we developed an interfacial engineering strategy for preparing a class of strongly coupled hybrid electrocatalysts for N₂ fixation. The hybrids exhibit superior N₂ reduction reaction activity with a high NH₃ Faradaic efficiency of 25.9% under ambient conditions. This strategy provides an approach to design advanced materials for ammonia production.

Electrocatalytic N₂ reduction reaction (NRR) into ammonia (NH₃), especially if driven by renewable energy, represents a potentially clean and sustainable strategy for replacing traditional Haber–Bosch process and dealing with climate change effect. However, electrocatalytic NRR process under ambient conditions often suffers from low Faradaic efficiency and high overpotential. Developing newly regulative methods for highly efficient NRR electrocatalysts is of great significance for NH₃ synthesis. Here, we propose an interfacial engineering strategy for designing a class of strongly coupled hybrid materials as highly active electrocatalysts for catalytic N₂ fixation. X-ray absorption near-edge spectroscopy (XANES) spectra confirm the successful construction of strong bridging bonds (Co–N/S–C) at the interface between CoS_x nanoparticles and NS-G (nitrogen- and sulfur-doped reduced graphene). These bridging bonds can accelerate the reaction kinetics by acting as an electron transport channel, enabling electrocatalytic NRR at a low overpotential. As expected, CoS₂/NS-G hybrids show superior NRR activity with a high NH₃ Faradaic efficiency of 25.9% at −0.05 V versus reversible hydrogen electrode (RHE). Moreover, this strategy is general and can be extended to a series of other strongly coupled metal sulfide hybrids. This work provides an approach to design advanced materials for ammonia production.