In Situ Synthesis Strategy for Hierarchically Porous Ni2P Polyhedrons from MOFs Templates with Enhanced Electrochemical Properties for Hydrogen Evolution

Zr-doped porous Ni2P nanoarray as a highly efficient electrocatalyst for hydrogen evolution reaction in alkaline seawater

The utilization of seawater electrolysis is recognized as a promising method for generating hydrogen as a substitute for conventional technology. Herein, the electrodes were fabricated byin-situgrowth of Zr-Ni2P arrays on a nickel foam substrate (Zr-Ni2P/NF) through a low-temperature hydrothermal and phosphating process. The Zr-Ni2P/NF can achieve efficient hydrogen evolution reaction (HER) performance in alkaline seawater electrolyte. This Zr-Ni2P/NF shows overpotentials as low as 197 and 274 mV at 100 and 500 mA cm-2for HER in alkaline seawater, respectively. Moreover, it exhibits strong stability for at least 50 h of electrolysis at a current density of 500 mA cm-2in alkaline seawater with the overpotential attenuation of 38 mV. The excellent performance and hierarchical structure advantages of Zr-Ni2P/NF provide new ideas for designing efficient seawater splitting electrocatalysts.

A Ni2P/NiMoOx nanocone electrocatalyst for efficient hydrogen evolution: tip-enhanced local electric field effect

The sluggish kinetics of the hydrogen evolution reaction (HER) result in a high overpotential in alkaline solutions. A high-curvature metal oxide heterostructure can effectively boost the electrocatalytic HER by leveraging the tip-enhanced local electric field effect. Herein, Ni2P/NiMoOx nanocones were synthesised on a nickel foam (NF) substrate by etching a metal-organic framework template. The Ni2P/NiMoOx nanocones on the NF substrate served as an advanced electrocatalyst for the HER. Analysis using the finite element method indicated that the high-curvature tips of the Ni2P/NiMoOx nanocones enhanced the local electric field, resulting in a higher concentration of hydrated K+ ions (K(H2O)6+), which facilitated water dissociation and accelerated the reaction kinetics. The tip-enhanced local electric field effect accelerates the mass transfer rate, and the heterostructure promotes charge transfer to activate the active center, thereby synergically enhancing the electrocatalytic reaction. The Ni2P/NiMoOx nanocone electrocatalyst exhibited low overpotentials of 49, 137 and 274 mV at 10, 100 and 500 mA cm-2, respectively, under alkaline conditions for the HER. In addition, the electrocatalyst demonstrated excellent stability over 200 h at 300 mA cm-2. This study provides a promising approach for developing efficient electrocatalysts that facilitate the HER in alkaline solutions.

Metal-organic framework-mediated construction of confined ultrafine nickel phosphide immobilized in reduced graphene oxide with excellent cycle stability for asymmetric supercapacitors

Transition metal phosphides (TMPs) with unique metalloid features have been promised great application potential in developing high-efficiency electrode materials for electrochemical energy storage. Nevertheless, sluggish ion transportation and poor cycling stability are the critical hurdles limiting their application prospects. Herein, we presented the metal-organic framework-mediated construction of ultrafine Ni₂P immobilized in reduced graphene oxide (rGO). Nano-porous two-dimensional (2D) Ni-metal-organic framework (Ni-MOF) was grown on holey graphene oxide (Ni(BDC)-HGO), followed by MOF-mediated tandem pyrolysis (carbonization and phosphidation; Ni(BDC)-HGO-X-P, X denoted carbonization temperature and P represented phosphidation). Structural analysis revealed that the open-framework structure in Ni(BDC)-HGO-X-Ps had endowed them with excellent ion conductivity. The Ni₂P wrapped by carbon shells and the PO bonds linking between Ni₂P and rGO ensured the better structural stability of Ni(BDC)-HGO-X-Ps. The resulting Ni(BDC)-HGO-400-P delivered a capacitance of 2333.3 F g^-1 at 1 A g^-1 in a 6 M KOH aqueous electrolyte. More importantly, Ni(BDC)-HGO-400-P//activated carbon, the assembled asymmetric supercapacitor with an energy density of 64.5 Wh kg^-1 and a power density of 31.7 kW kg^-1, almost maintained its initial capacitance after 10,000 cycles. Furthermore, in situ electrochemical-Raman measurements were exploited to demonstrate the electrochemical changes of Ni(BDC)-HGO-400-P throughout the charging and discharging processes. This study has further shed light on the design rationality of TMPs for optimizing supercapacitor performance.

Coupling heterostructured CoP-NiCoP nanopin arrays with MXene (Ti3C2Tx) as an efficient bifunctional electrocatalyst for overall water splitting

Developing a highly effective bifunctional electrocatalyst for alkaline-condition electrochemical water splitting is both essential and challenging. The work presented here successfully synthesizes and employs a heterostructured CoP-NiCoP ultra-long nanopin array in situ growing on MXene (Ti₃C₂T_x) as a stable bifunctional electrocatalyst for electrochemical water-splitting. The heterogeneous structure formed by CoP nanoparticles and NiCoP nanopins provides extra active sites for water-splitting. Also, Ti₃C₂T_x works as a support substrate during electrochemical operations, accelerating mass transfer, ion transport, and rapid gas product diffusion. Meanwhile, throughout the catalytic process, the dense nanopin arrays shield Ti₃C₂T_x from further oxidation. At a result, the CoP-NiCoP-Ti₃C₂T_x (denoted as CP-NCP-T) demonstrated excellent catalytic activity, with overpotentials of just 46 mV for hydrogen evolution at 10 mA cm^-2 and 281 mV for oxygen evolution at 50 mA cm^-2. Furthermore, in 1.0 M KOH solution, the outstanding bifunctional electrode (CP-NCP-T || CP-NCP-T) exhibits efficient electrochemical water splitting activity (1.54 V@10 mA cm^-2) and outperforms the comparable device Pt/C || IrO₂ (1.62 V@10 mA cm^-2).

Solvent-induced structural regulation over Ni2P/CNT hybrids towards boosting the performance of supercapacitors

Although nickel-based phosphides have attracted increasing attention due to their good theoretical specific capacity, the poor rate capability weakness their advantage in electrochemical energy storage. It is, however, challenging to improve these issues by only adjusting composition. Here, we employ a synergistic strategy, both hybridizing with highly conductive materials and regulating morphology, to enhance the electrochemical performance of Ni₂P. Based on solvent-induced effects, flower/rod-like [CH₃NH₃][Ni(HCOO)₃] precursors hybridized with CNTs are prepared and then employed as templates to construct flower/rod-like Ni₂P/CNT hybrids via a gas-solid phosphorization method. Benefiting from the synergistic advantages of both structure and components, the flower-like Ni₂P/CNT hybrid, as an electrode materials for supercapacitor, exhibit outstanding specific capacitance of up to 1480 F g^-1 at 1 A g^-1, as well as improved rate capability. Additionally, the assembled asymmetric supercapacitor (Ni₂P/CNTs//AC, ASC) delivers a high capacitance retention of up to 83.5% after 5000 cycles at 10 A g^-1, and an expected energy density of 25.2 W h kg^-1 at a power density of 749.8 W kg^-1.

Ni5P4-NiP2-Ni2P Nanocomposites Tangled with N-Doped Carbon for Enhanced Electrochemical Hydrogen Evolution in Acidic and Alkaline Solutions

Heterostructured non-precious metal phosphides have attracted increasing attention in the development of high-performance catalysts for hydrogen evolution reaction (HER), particularly in acidic media. Herein, a catalyst composed of ternary Ni5P4-NiP2-Ni2P nanocomposites and N-doped carbon nanotubes/carbon particulates (Ni5P4-NiP2-Ni2P/NC) was prepared from a Ni-containing hybrid precursor through approaches of a successive carbonization and phosphating reaction. Benefiting from the synergistic effect from three-component nickel phosphides and the support role of porous carbon network, the Ni5P4-NiP2-Ni2P/N-doped carbon catalyst presents the promising HER performance with overpotentials of 168 and 202 mV at the current density of 10 mA cm−2 and Tafel slopes of 69.0 and 74 mV dec−1 in both acidic and alkaline solutions, respectively, which surpasses the Ni2P/N-doped carbon counterpart. This work provides an effective strategy for the preparation and development of highly efficient HER non-precious metal electrocatalysts by creating heterostructure in acidic and alkaline media.

Interfacial Strain-Modulated Nanospherical Ni2 P by Heteronuclei-Mediated Growth on Ti3 C2 Tx MXene for Efficient Hydrogen Evolution

Interface modulation of nickel phosphide (Ni₂ P) to produce an optimal catalytic activation barrier has been considered a promising approach to enhance the hydrogen production activity via water splitting. Herein, heteronuclei-mediated in situ growth of hollow Ni₂ P nanospheres on a surface defect-engineered titanium carbide (Ti₃ C₂ T_x ) MXene showing high electrochemical activity for the hydrogen evolution reaction (HER) is demonstrated. The heteronucleation drives intrinsic strain in hexagonal Ni₂ P with an observable distortion at the Ni₂ P@Ti₃ C₂ T_x MXene heterointerface, which leads to charge redistribution and improved charge transfer at the interface between the two components. The strain at the Ni₂ P@Ti₃ C₂ T_x MXene heterointerface significantly boosts the electrochemical catalytic activities and stability toward HER in an acidic medium via a combination between experimental results and theoretical calculations. In a 0.5 m H₂ SO₄ electrolyte, the Ni₂ P@Ti₃ C₂ T_x MXene hybrid shows excellent HER catalytic performance, requiring an overpotential of 123.6 mV to achieve 10 mA cm^-2 with a Tafel slope of 39 mV dec^-1 and impressive durability over 24 h operation. This approach presents a significant potential to rationally design advanced catalysts coupled with 2D materials and transition metal-based compounds for state-of-the-art high efficiency energy conversions.

Nitrogen Disturbance Awakening the Intrinsic Activity of Nickel Phosphide for Boosted Hydrogen Evolution Reaction

Nickel phosphide (Ni₂ P) has emerged as a promising candidate to substitute Pt-based catalysts for hydrogen evolution reaction (HER) due to the hydrogenase-like catalytic mechanism and concomitantly low cost. However, its catalytic activity is still not comparable to that of noble-metal-based catalysts, and innovative strategies are still urgently needed to further improve its performance. Herein, a self-supported N-doped Ni₂ P on Ni foam (N-Ni₂ P/NF) was rationally designed and fabricated through a facile NH₄ H₂ PO₂ -assisted gas-solid reaction process. As an HER catalyst in alkaline medium, the obtained N-Ni₂ P/NF revealed excellent electrocatalytic performance with a distinctly low overpotential of 50 mV at 10 mA cm^-2 , a small Tafel slope of 45 mV dec^-1 , and long-term stability for 25 h. In addition, the spectroscopic characterizations and density functional theory calculations confirmed that the incorporation of N regulated the original electronic structure of Ni₂ P, enhanced its intrinsic catalytic property, optimized the Gibbs free energy of reaction intermediates, and ultimately promoted the HER process. This work provides an atomic-level insight into the electronic structure modulation of metal phosphides and opens an avenue for developing advanced transition metal phosphides-based catalysts.

Cation-Vacancy-Enriched Nickel Phosphide for Efficient Electrosynthesis of Hydrogen Peroxides

Electrocatalytic hydrogen peroxide (H₂ O₂ ) synthesis via the two-electron oxygen reduction reaction (2e ORR) pathway is becoming increasingly important due to the green production process. Here, cationic vacancies on nickel phosphide, as a proof-of-concept to regulate the catalyst's physicochemical properties, are introduced for efficient H₂ O₂ electrosynthesis. The as-fabricated Ni cationic vacancies (V_Ni )-enriched Ni_{2- x} P-V_Ni electrocatalyst exhibits remarkable 2e ORR performance with H₂ O₂ molar fraction of >95% and Faradaic efficiencies of >90% in all pH conditions under a wide range of applied potentials. Impressively, the as-created V_Ni possesses superb long-term durability for over 50 h, suppassing all the recently reported catalysts for H₂ O₂ electrosynthesis. Operando X-ray absorption near-edge spectroscopy (XANES) and synchrotron Fourier transform infrared (SR-FTIR) combining theoretical calculations reveal that the excellent catalytic performance originates from the V_Ni -induced geometric and electronic structural optimization, thus promoting oxygen adsorption to the 2e ORR favored "end-on" configuration. It is believed that the demonstrated cation vacancy engineering is an effective strategy toward creating active heterogeneous catalysts with atomic precision.

Uniform H-CdS@NiCoP core-shell nanosphere for highly efficient visible-light-driven photocatalytic H2 evolution

Constructing highly efficient and cost-effective photocatalyst system has been a big challenge for photocatalysis. Herein, CdS nanosphere (N-CdS), hollow CdS (H-CdS) and a series of H-CdS@NiCoP core-shell nanospheres have been successfully prepared via a facile hydrothermal method. The activity test showed that H-CdS exhibited higher photocatalytic activity (3.34 mmol g^-1h^-1) compared with N-CdS (0.99 mmol g^-1h^-1) under visible light irradiation (λ ≥ 420 nm), suggesting that hollow structure could effectively improve photocatalytic activity. Moreover, the H-CdS@NiCoP-7 wt% displayed a maximum photocatalytic H₂ evolution rate of 13.47 mmol g^-1h^-1, which was about 4 times and 2.5 times higher than that of pristine H-CdS and H-CdS@Pt-3 wt%, respectively. Furthermore, H-CdS@NiCoP-7 wt% exhibited a good stability during 20 h test. The physicochemical properties were characterized by XRD, SEM, TEM, XPS, UV-vis DRS, PL and photoelectrochemical technique. The results showed that NiCoP addition can construct p-n junction with H-CdS and effectively promote the charge transfer from CdS to NiCoP, which improved the photocatalytic hydrogen evolution activity. This work revealed that NiCoP could react as an excellent co-catalyst for enhancing H-CdS photocatalytic activity.

FeNi2P three-dimensional oriented nanosheet array bifunctional catalysts with better full water splitting performance than the full noble metal catalysts

The 3D (three-dimensional) oriented nanosheet array FeNi₂P electrocatalyst grown on carbon cloth (FeNi₂P/CC) is explored in this work. This unique 3D oriented nanosheet array structure can expose more catalytic active sites, promote the penetration of electrolyte solution on the catalyst surface, and facilitate the transfer of ions, thus speeding up the kinetic process of Hydrogen evolution reaction (HER) and Oxygen evolution reaction (OER). At the current densities of 10 mA/cm² in 1 M KOH solution, the HER overpotential (71 mV) of the FeNi₂P/CC self-supporting electrode is very close to that of noble metal HER catalyst of 20% Pt/C (54 mV), and its OER overpotential (210 mV) is 34% lower than that of the precious metal OER catalyst of RuO₂ (318 mV), demonstrating the excellent electrocatalytic performance of the FeNi₂P/CC catalyst. Moreover, the cell voltage for full water splitting (at 10 mA/cm² current densities) of the FeNi₂P/CC bifunctional electrode cell is 1.52 V, which is 3.8% lower than that of the full noble-metal electrode reference cell (RuO₂ || Pt/C, 1.58 V), suggesting that this FeNi₂P/CC bifunctional catalyst is likely to replace precious metals to reduce the costs in full water splitting application. According to density functional theory (DFT) calculation results, the introduction of iron atom can change the electronic structure of the Ni₂P, so it can reduce the adsorption energy of hydrogen and oxygen, and facilitate the adsorption and desorption of hydrogen and oxygen on the surface of the catalyst, improving its performance of HER and OER.

A chainmail effect of ultrathin N-doped carbon shell on Ni2P nanorod arrays for efficient hydrogen evolution reaction catalysis

Exploring innovation strategies has huge potential to significantly improving both activity and stability of current catalysts. Here, a chainmail design is proposed to enable the electronic interaction of ultrathin nitrogen-doped carbon shell with Ni₂P nanorod core arrayed on nickel foam (Ni₂P@NC/NF) for simultaneously promoting the activity and stability in both alkaline and neutral hydrogen evolution reaction (HER). The easy penetration of valence electrons from active Ni₂P core to NC shell enables the obvious improvement of HER performance compared to pure Ni₂P. In 1 M KOH and 1 M PBS solution, the resultant Ni₂P@NC/NF requires the ultralow overpotentials of only 93 and 96 mV to drive the current density of 10 mA cm^-2 with the Faradaic efficiency of 96% and 94%, respectively. Remarkably, such a chainmail design also reveals an obviously improved stability with almost negligible performance degradation under the current density of 20 mA cm^-2 for 30 h. Theoretical calculations confirm that the nitrogen-doped carbon shell improves the durability of transition metal phosphides by increasing the dissolution resistance of Ni atoms. The proposed concept may create a new pathway for synchronizing high activity and robust stability in manipulating heterogeneous catalytic properties.

One-Pot Synthesis of B/P-Codoped Co-Mo Dual-Nanowafer Electrocatalysts for Overall Water Splitting

Exploring electrocatalysts with satisfactory activity and durability has remained a long-lasting target for electrolyzing water, which is particularly significant for sustainable hydrogen fuel production. Here, we report a quaternary B/P-codoped transition metal Co-Mo hybrid as an efficient alternative catalyst for overall water splitting. The Co-Mo-B-P/CF dual nanowafers were deposited on a copper foam by double-pulse electrodeposition, which is favorable for achieving a nanocrystalline structure. The Co-Mo-B-P/CF catalyst shows a high catalytic activity along with good long-term stability in 1.0 M KOH solutions for both the hydrogen and oxygen evolution reactions, requiring 48 and 275 mV to reach 10 mA cm^-2, respectively. The synergetic effect between Co-Mo and doped B and P elements is mainly attributed to the excellent bifunctional catalysis performance, while the dual-nanowafer structure endows Co-Mo-B-P with numerous catalytical active sites enhancing the utilization efficiency of atoms. Moreover, the catalytic capability of Co-Mo-B-P/CF as a bifunctional electrocatalyst for the overall water splitting is proved, with the current density of 10 mA cm^-2 accomplished at 1.59 V. After the stability test for overall water splitting at 1.59 V for 24 h, the activity almost remains unchanged. The features of excellent electrocatalytic activity, simple preparation, and inexpensive raw materials for Co-Mo-B-P/CF as a bifunctional catalyst hold great potentials for overall water splitting.

FeCoP2 Nanoparticles Embedded in N and P Co-doped Hierarchically Porous Carbon for Efficient Electrocatalytic Water Splitting

The design and synthesis of low-cost and efficient bifunctional electrocatalysts for water splitting are critical and challenging. Hereby, a bimetallic phosphide embedded in a N and P co-doped porous carbon (FeCoP₂@NPPC) material was synthesized by using sustainable biomass-derived N- and P-containing carbohydrates and non-noble metal salts as precursors. The obtained material exhibits good catalytic activities in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. The bimetallic alloy phosphide (FeCoP₂) is the active site for electrocatalysis. Theoretical calculation indicates that the sub-layer Fe atoms and top-layer Co atoms in FeCoP₂ exhibit a synergistic effect for enhanced electrocatalytic performance. The carbon matrix around the FeCoP₂ can prevent the corrosion during the catalytic reactions. The hierarchically porous structure of the FeCoP₂@NPPC material can promote the transfer of electrons and electrolyte, and increase the contact area of the active sites and electrolytes. N- and P-containing functionalities improve the wetting and conductivity properties of the porous carbon. Due to the synergistic effects, FeCoP₂@NPPC requires a low overpotential of 114 and 150 mV at the current density of 10 mA cm^-2 for HER in 0.5 M H₂SO₄ and 1.0 M KOH, and an overpotential of 236 mV for OER in 1.0 M KOH solution, which are much lower than those of FeP@NPPC and CoP@NPPC. Based on the density functional theory calculation, FeCoP₂ yields the smallest Gibbs free energy change of rate-determining step among the samples, which leads to better electrochemical performances. In addition, when FeCoP₂@NPPC was used as a bifunctional catalyst in water splitting, the electrolyzer needed a low voltage of 1.60 V to deliver the current density of 10 mA cm^-2. Furthermore, this work provides a strategy for preparing sustainable, stable, and highly active electrocatalysts for water splitting.

Linker Deficiency, Aromatic Ring Fusion, and Electrocatalysis in a Porous Ni8-Pyrazolate Network

The cruciform linker molecule here features two designer functions: the pyrazole donors for framework construction, and the vicinal alkynyl units for benzannulation to form nanographene units into the Ni₈-pyrazolate scaffold. Unlike the full 12 connections of the Ni₈(OH)₄(H₂O)₂ clusters in other Ni₈-pyrazolate networks, significant linker deficiency was observed here, leaving about half of the Ni(II) sites capped by acetate ligands, which can be potentially removed to open the metal sites for reactivity. The crystalline Ni₈-pyrazolate scaffold also retains the crystalline order even after thermal treatments (up to 300 °C) that served to partially graphitize the neighboring alkyne units. The resultant nanographene components enhance the electroactive properties of the porous hosts, achieving hydrogen evolution reaction (HER) activity that rivals that of topical nickel/palladium-enabled materials.

Improved ionic diffusion and interfacial charge/mass transfer of ZIF-67-derived Ni–Co-LDH electrodes with bare ZIF-residual for enhanced supercapacitor performance

The crystallization of Ni–Co-LDH and the morphology of the hierarchical structure can be simply optimized to achieve improved ionic diffusion and reduce reaction resistance of charge/mass transfer between the electrode/electrolyte interfaces.

Nanostructured metal phosphides: from controllable synthesis to sustainable catalysis

Metal phosphides (MPs) with unique and desirable physicochemical properties provide promising potential in practical applications, such as the catalysis, gas/humidity sensor, environmental remediation, and energy storage fields, especially for transition metal phosphides (TMPs) and MPs consisting of group IIIA and IVA metal elements. Most studies, however, on the synthesis of MP nanomaterials still face intractable challenges, encompassing the need for a more thorough understanding of the growth mechanism, strategies for large-scale synthesis of targeted high-quality MPs, and practical achievement of functional applications. This review aims at providing a comprehensive update on the controllable synthetic strategies for MPs from various metal sources. Additionally, different passivation strategies for engineering the structural and electronic properties of MP nanostructures are scrutinized. Then, we showcase the implementable applications of MP-based materials in emerging sustainable catalytic fields including electrocatalysis, photocatalysis, mild thermocatalysis, and related hybrid systems. Finally, we offer a rational perspective on future opportunities and remaining challenges for the development of MPs in the materials science and sustainable catalysis fields.

CoMo-bimetallic N-doped porous carbon materials embedded with highly dispersed Pt nanoparticles as pH-universal hydrogen evolution reaction electrocatalysts

The hydrogen evolution reaction is a key half reaction for water electrolysis and is of great significance. Pt-based nanomaterials are promising candidates for HER electrocatalysts. However, the high price of platinum and poor durability impede their practical applications. Herein, a new CoMo-bimetallic hybrid zeolite imidazolate framework is employed to load Pt nanoparticles in a highly dispersed manner as a precursor to synthesize an efficient pH-universal HER electrocatalyst (PtCoMo@NC), which displays overpotentials of 26, 51, and 66 mV at a current density of 10 mA cm^-2 in acidic, basic, and neutral media, respectively. The strong synergistic effect of highly dispersed multi-type catalytic species, including cobalt, molybdenum carbide, and platinum (4.7%) promotes the catalytic activity in the HER process. Meanwhile, the aggregation of Pt nanoparticles is greatly restrained by the carbon matrix so that a brilliant long-time durability of 12 hours and a negligible current decrease in the LSV curve after 10 000 CV cycles are achieved.

Nickel Phosphide Electrocatalysts for Hydrogen Evolution Reaction

The production of hydrogen through electrochemical water splitting driven by clean energy becomes a sustainable route for utilization of hydrogen energy, while an efficient hydrogen evolution reaction (HER) electrocatalyst is required to achieve a high energy conversion efficiency. Nickel phosphides have been widely explored for electrocatalytic HER due to their unique electronic properties, efficient electrocatalytic performance, and a superior anti-corrosion feature. However, the HER activities of nickel phosphide electrocatalysts are still low for practical applications in electrolyzers, and further studies are necessary. Therefore, at the current stage, a specific comprehensive review is necessary to focus on the progresses of the nickel phosphide electrocatalysts. This review focuses on the developments of preparation approaches of nickel phosphides for HER, including a mechanism of HER, properties of nickel phosphides, and preparation and electrocatalytic HER performances of nickel phosphides. The progresses of the preparation and HER activities of the nickel phosphide electrocatalysts are mainly discussed by classification of the preparation method. The comparative surveys of their HER activities are made in terms of experimental metrics of overpotential at a certain current density and Tafel slope together with the preparation method. The remaining challenges and perspectives of the future development of nickel phosphide electrocatalysts for HER are also proposed.

In situ construction and post-electrolysis structural study of porous Ni2P@C nanosheet arrays for efficient water splitting

Carbon-confined Ni₂P porous nanosheet arrays functioned as a superior water-splitting catalyst. Impressively, this porous-hybrid catalyst just required an OER overpotential of 243 mV to deliver 15 mA cm⁻² owing to the formation of γ-NiOOH layer.

Temperature controlled diffusion of hydroxide ions in 1D channels of Ni-MOF-74 for its complete conformal hydrolysis to hierarchical Ni(OH)2 supercapacitor electrodes

Conformal hydrolysis of MOF precursors is a promising strategy to prepare hierarchical metal hydroxide electrode materials on a large scale with low cost and high efficiency. However, a complete transformation is challenging due to the normal "outside-in" conversion process. After studying the hydrolysis of Ni-MOF-74, which has regular 1D channels, we suggest that the transformation to Ni(OH)2 can occur simultaneously outside and within the precursor depending on the treatment temperature. Molecular dynamics simulations reveal that a higher temperature weakens the steric effects of OH- ions and facilitates the diffusion in the regular channels, and therefore, a complete transformation from Ni-MOF-74 to Ni(OH)2 is achieved. It is for the first time demonstrated that the 1D channels of MOFs are utilized for the complete conformal hydrolysis of Ni-MOF-74 to Ni(OH)2 electrode materials. Meanwhile, we also perform pioneering work illustrating that the complete conformal hydrolysis is the key to the improved supercapacitor performances of the MOF-derived Ni(OH)2 electrodes. The prepared Ni(OH)2 electrode under the optimized conditions has a specific capacity of 713.2 C g-1 at a current density of 1 A g-1, which is at least 28% larger than those of the Ni(OH)2 prepared at other temperatures. The detailed analyses based on CV and EIS of the obtained Ni(OH)2 electrodes indicate that the residual MOFs within electrodes due to incomplete hydrolysis significantly influence the diffusion length and diffusion efficiency of OH-, drastically lowering the supercapacitor performances.

Cobalt Nanoparticles Embedded into N-Doped Carbon from Metal Organic Frameworks as Highly Active Electrocatalyst for Oxygen Evolution Reaction

Cystosepiment-like cobalt nanoparticles@N-doped carbon composite named Co-NPs@NC with highly efficient electrocatalytic performance for oxygen evolution reaction was prepared from carbonization of N-doped Co-MOFs. The optimized Co-NPs@NC-600 shows overpotentials of 315 mV to afford a current density of 10 mA·cm-2. Meanwhile, the electrocatalys presents excellent long-term durability. The outstanding electrocatalytic performance can be attributed to the unique cystosepiment-like architecture with high specific surface area (214 m2/g), high conductivity of N-doped carbon and well-distributed active sites.

Two-Dimensional Zeolitic Imidazolate Framework-L-Derived Iron-Cobalt Oxide Nanoparticle-Composed Nanosheet Array for Water Oxidation

Rational design of various functional nanomaterials using MOFs as a template provides an effective strategy to synthesize electrocatalysts for water splitting. In this work, we reported that an iron-cobalt oxide with 2D well-aligned nanoflakes assembling on carbon cloth (Fe-Co₃O₄ NS/CC), fabricated by an anion-exchange reaction followed by an annealing process, could serve as a high-performance oxygen-evolving catalyst. Specifically, the zeolitic imidazolate framework-L-Co nanosheet array (ZIF-L-Co NS/CC) was synthesized through a facile ambient liquid-phase deposition reaction, and then reacted with [Fe(CN)₆]^3- ions as precursors during the anion-exchange reaction at room temperature. Finally, the Fe-Co₃O₄ NS/CC was obtained via annealing treatment. On account of the compositional and structural superiority, this 3D monolithic anode exhibited outstanding electrocatalytic performance with a low overpotential of 290 mV to obtain a geometrical current density of 10 mA cm^-2 and good durability for water oxidation in base.

Superstructure of a Metal-Organic Framework Derived from Microdroplet Flow Reaction: An Intermediate State of Crystallization by Particle Attachment

Understanding the crystallization pathway is of fundamental importance in controlling structures and functionalities for metal-organic frameworks (MOFs), but only few studies have been reported on the mechanism of crystallization for MOFs to date. Here, by using a microdroplet flow (MF) reaction technique, we successfully revealed the different status of HKUST-1 during its crystal growth process. The morphologies and structures of crystals at different stages were recorded and characterized by scanning electron microscopy, transmission electron microscopy, and small-angle X-ray diffraction. Experimental observations clearly demonstrate a process of crystallization by particle attachment (CPA) for crystal growth of HKUST-1 under MF conditions. The superstructure of HKUST-1, which is assembled from oriented attachment of nanosized particles of HKUST-1, is observed at early stage of crystal growth. This type of superstructure gradually transforms to true single crystals through a ripening effect upon increasing residence time, accompanied by increase in dimensions of crystals. Thus, the superstructure is the intermediate state during crystallization and acts as the bridge between disordered reactants and highly ordered single crystals. Based on these findings, the crystal growth of HKUST-1 in MF reaction can be elucidated as a process involving three steps: the generation of nanosized primary particles, the following assembly of the primary particles into a superstructure, and the ripening of superstructure into a crystal. Furthermore, the superstructure of HKUST-1 shows superior performance for CO₂ and CH₄ adsorptions. The CPA mechanism in the crystallization of HKUST-1 demonstrated in this work is in clear contrast to the monomer-by-monomer addition mechanism in classic models of crystal growth. This mechanism could have important reference meaning for understanding the crystal growth mechanism of other type of MOFs or other special morphologies.

Plasma enabled non-thermal phosphorization for nickel phosphide hydrogen evolution catalysts

Plasma activates inert phosphorous vapour to prepare nickel phosphide nanosheets at mild temperature for hydrogen evolution from water electrolysis.

A MOF-derived coral-like NiSe@NC nanohybrid: an efficient electrocatalyst for the hydrogen evolution reaction at all pH values

A coral-like NiSe@NC nanohybrid as an effective electrocatalyst for the hydrogen evolution reaction (HER) at all pH values, constructed via the in situ selenation of a Ni-MOFs precursor, is reported. The electrocatalyst shows overpotentials of 123 mV, 250 mV and 300 mV in 0.5 M H2SO4, 1.0 M KOH and 1.0 M PBS, respectively, to afford a current density of 10 mA cm-2. Meanwhile, NiSe@NC also exhibits a small Tafel slope and superior long-term stability over a wide pH range. The excellent electrocatalytic performance should be ascribed to the unique coral-like structure with a large BET specific surface area (125.4 m2 g-1) and mesoporous features, as well as synergistic effects between NiSe nanocrystals and highly conductive N-doped porous carbon.

MOF-Derived Porous Ni2P/Graphene Composites with Enhanced Electrochemical Properties for Sensitive Nonenzymatic Glucose Sensing

Herein, we report a high-performance electrocatalyst by orientationally growing Ni₂P nanoparticles in situ on graphene film (Ni₂P/G) for nonenzymatic glucose sensors in alkaline media. The combination of highly active Ni₂P and stable graphene film with rapid conductivity enables this composite to display excellent electrochemical activity toward glucose with enhanced electron transfer rate and steadiness. With Ni-MOF-74 as a precursor, Ni₂P/G showed even metal distribution, massive exposure of active sites, and spatially ordered structure. Benefiting from the synergistic reaction of Ni₂P particles and graphene, this metal-organic frameworks (MOF)-derived composite exhibited high electrocatalytic activity and specificity toward glucose electrooxidation. Under optimized conditions, a wide linear response was obtained from 5 μM to 1.4 mM with a detection limit of 0.44 μM. Furthermore, an excellent linear response ( R² = 0.9897) was also obtained by a Ni₂P/G modified electrode in human serum with the concentration of glucose ranging from 1 to 8 mM, indicating that the Ni₂P/G platform could be utilized for glucose monitoring in practical life.