Metallic Co,CoS, and P co-doped N enriched carbon derived from ZIF-67 as an efficient catalyst for hydrogen evolution reaction

Exploring non-precious materials with efficient electrocatalytic performance to replace the precious Pt-based materials for hydrogen evolution reaction (HER) is still a great challenge now. Herein, metallic Co, CoS, and P co-doped N enriched carbon (CoSP/NC) was successfully fabricated by using ZIF-67 as precursor via a facile pyrolysis, sulphurization, and phosphorization process for HER application. ZIF-67 was transformed into metallic Co doped N enriched carbon (Co/NC) undergoing the treatment of high temperature. After being sulphurized, part of metallic Co was transformed into CoS and attached firmly on the surface of the catalyst. P element was well dispersed on the catalyst during the phosphorization process. The fabricated CoSP/NC exhibits the optimal HER activity with the superior overpotential of 183 mV at 10 mA cm⁻² and the lowest Tafel slope of 64.25 mV dec⁻¹. Furthermore, CoSP/NC shows superior durability. The excellent HER performance may be ascribed to the abundant active sites, firm structure, and superior electrical conductivity of the carbon. Thus, this work provides a new strategy to fabricate non-precious materials with excellent HER performance for the following researchers.     

3-Dimensional flower-like clusters of CoNiP nanofoils in-situ grown on randomly-dispersed rGO-Nanosheets with superior electrocatalysis for hydrogen evolution reactions

It has been being an interesting challenge to develop novel electrocatalysts with advantageous nanostructures and thereby-improved catalytic performance for hydrogen evolution reaction (HER) over the past years. Herein, we report on the flower-like clusters of CoNiP nanofoils thickly grown on the randomly-interconnected reduced graphene oxide (rGO) nanosheets (CoNiP-NF/rGO) of 3-dimensional framework architecture, which has been successfully achieved via an optimized solvothermal process with Ni-doped ZIF-67 (Ni-ZIF-67) dodecahedral particles as the precursor and graphene oxide (GO) nanosheets as the substrate for the in-situ growth of flower-like CoNi-hydroxides nanofoils, as well as a following topotactic transformation in a controlled phosphorization. Benefiting from its distinctly advantageous nanostructures featured with extremely high specific surface area, enriched catalytic active sites and enhanced electronic transportation, the as-prepared CoNiP-NF/rGO exhibits an excellent electrocatalytic performance of HER with an onset overpotential of 33 mV, an overpotential of 82 mV at 10 mA cm⁻², a Tafel slope of 37 mV dec⁻¹ and a high chemical stability in acidic solutions. Such an advantageous nanostructure and its positive influences on the electrocatalytic performance are useful for the preparation of other nonprecious metal electrocatalysts.     

Cobalt phosphide nanoparticles embedded in 3D N-doped porous carbon for efficient hydrogen and oxygen evolution reactions

An electrocatalyst based on a unique three-dimensional (3D) N-doped porous carbon sheet networks embedded with CoP₂ nanoparticles (CoP₂@3D-NPC) was synthesized by a facile pyrolysis process as well as an in-situ phosphatization method. The improved CoP₂@3D-NPC hybrid materials show excellent electrocatalytic activity toward HER and OER. This material provides a low overpotential of 126 mV at 10 mA cm⁻² in 0.5 M H₂SO₄ and 167 mV at 20 mA cm⁻² in 1.0 M KOH for HER with a small Tafel slope value of 59 mV dec⁻¹, respectively. Besides, it is also active for the OER under alkaline conditions. Such a prominent property of the CoP₂@3D-NPC electrocatalyst could be attributed to its excellent electrical conductivity of 3D carbon substrate, strong synergistic effect between CoP₂ nanoparticles and carbon nanosheet as well as extra active sites created by the N-doped structure.     

The catalytic performance enhancement of Ni2P electrocatalysts for hydrogen evolution reaction by carbon-based substrates

Combination of catalytic active components with substrates is deemed to be a promising approach to pursue high active and stable catalysts. Wherein, carbon-based materials as a kind of frequently-used substrates are well developed, and thus the different effects of them on catalytic active components deserve investigating and contrasting. In this work, well dispersive and ultrafine Ni₂P nanoparticles supported on N-doped reduced graphene oxide (N-RGO) were synthesized through a facial hydrothermal process and subsequent phosphorization. The prepared Ni₂P/N-RGO demonstrates a superior electrocatalytic activity towards hydrogen evolution reaction (HER) in 0.5 M H₂SO₄ solution with a low onset overpotential (80 mV) and small Tafel slope (93.1 mV dec⁻¹). Additionally, as compared with other representative carbon materials (carbon black (C) and carbon nanotubes (CNTs)) in the perspective of specific surface area (SSA), conductivity and electronic interaction in particular, N-RGO demonstrates a preeminent promotional effect as a substrate of Ni₂P.     

Metal-organic frameworks derived self-supported Ni2P nanorod arrays for electrocatalytic hydrogen evolution

The development of efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) is of importance. Herein, we demonstrate a self-supported Ni₂P nanostructure with nanorod arrays morphology, fabricated by directly growing metal-organic frameworks (MOFs) on the commercial nickel foam prior to phosphorization treatment, as an electrocatalyst for HER. This electrocatalyst exhibits remarkable electrocatalytic HER activity in an alkaline electrolyte, affording current densities of 10 and 100 mA cm^?2 at the overpotentials of 120 and 168 mV, respectively, accompanied with a low Tafel slope of 37 mV dec^?1. Furthermore, this electrocatalyst shows a current density of 105 mA cm^?2, and this current density can be retained for more than 20 h, suggesting its superior stability. This remarkable HER performance is believed a result of superiority for its structural integrality and mechanical stability.     

Porous coordination polymer-derived ultrasmall CoP encapsulated in nitrogen-doped carbon for efficient hydrogen evolution in both acidic and basic media

Exploiting high-efficient and stable non-precious metal-based electrocatalysts toward hydrogen evolution reaction (HER) is of enormous significance to address the shortage of global power source, but there remain major challenges. Here we present a facile and controllable strategy to synthesize a strongly coupled ultrasmall-cobalt phosphide/nitrogen-doped graphitic carbon (u-CoP@NC) hybrid structure via phosphorization from a porous coordination polymer (PCP) precursor. The PCP-derived u-CoP@NC exhibits remarkable activity and stability for HER, achieving a current density of 10 mA cm⁻² with a low overpotential of 131 mV in acidic media and 111 mV in basic media. The corresponding Tafel slopes present in acidic and basic media are 62.7 and 70.3 mV dec⁻¹, respectively. Results reveal that the enhanced electrocatalytic performance of u-CoP@NC originates from the strongly coupled u-CoP nanoparticles and graphitic carbon layer, and the perfect dispersity of the active sites. This research opens up new avenues for designing earth-abundant metal-based electrocatalysts with high capability for water splitting applications.     

Synthesis of Pt nano catalyst in the presence of carbon monoxide: Superior activity towards hydrogen evolution reaction

The effect of carbon monoxide (CO) on the reduction of Pt ion to metallic Pt is studied. The modified GC electrode with platinum metal synthesized in the presence of CO shows excellent activity for hydrogen evolution reaction (HER). Despite the decrease in the loading of platinum (4.5 × 10⁻⁴ mg cm⁻²) a substantial increase in its electrocatalytic activity towards HER is observed in a sulfuric acid environment. The observed electrocatalytic activity is comparable to available commercial catalysts like Pt/C. Tafel slope was obtained to be 34 mV.dec^−1, and the overpotential was acquired to be 31 mV at the mass activity of 10 mA mg⁻¹ were observed which was very close to kinetic parameters of Pt/C catalyst.     

Ni foil supported FeNiP nanosheet coupled with NiS as highly efficient electrocatalysts for hydrogen evolution reaction

The investigation and development of bimetallic phosphosulphide electrocatalyst with low cost and abundant reserves is extremely significant for the improvement of the efficiency of hydrogen evolution reaction (HER), while it remains a challenge. Herein, we explored a feasible method to prepare three-dimensional (3D) self-supported FeNiP-S/NF-5 nanosheet arrays on Ni foil (NF) by hydrothermal method and in situ phosphorization and following sulfurization treatment. The as-obtained FeNiP-S/NF-5 only needs a potential of 183 mV vs. RHE to reach 20 mA cm⁻², which is smaller than that of FeNiP/NF (187 mV vs. RHE) and FeNiS/NF-5 (239 mV vs. RHE), presenting excellent electrocatalytic stability. Such outstanding performance of the FeNiP-S/NF-5 can be attributed to following several reasons: (i) bi-metallic phosphide and sulphide have the high intrinsic activity because of its synergistic effect; (ii) the 3D nanosheet arrays structure of FeNiP-S/NF-5 is conducive to expose plentiful active sites and facilitate the electrolyte penetration along with electron transportation; (iii) the sulfurization process followed phosphorization treatment could further optimize their electronic structure and inhibited the surface oxidation of catalyst in the catalytic process.     

High electrocatalytic effect of Au–Pd alloy nanoparticles electrodeposited on microwave assisted sol–gel-derived carbon ceramic electrode for hydrogen evolution reaction

Various Au–Pd bimetallic nanoparticles were electrodeposited on microwave irradiated carbon ceramic electrodes (MWCCE). Au:Pd molar ratios of 75:25, 50:50 and 25:75 were electrodeposited on MWCCE and their electrocatalytic activities for hydrogen evolution reaction (HER) were evaluated. Among them, the alloy with Au:Pd molar ratio of 25:75 showed highest electrocatalytic activity for HER. The structure and nature of these alloys were characterized by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, inductively coupled plasma, and cyclic voltammetry. Alloying degree of bimetallic nanoparticles and electrodeposition time were optimized. The electrocatalytic activity of bimetallic nanoparticles was also compared with individual non-alloyed Au and Pd catalysts and the results showed that alloy nanoparticles have higher electrocatalytic activity for hydrogen evolution. The Tafel slopes ranges are obtained from 136 mV dec⁻¹ to 165 mV dec⁻¹ for HER on bare and modified MWCCE and kinetic parameters show that the Volmer step must control the HER. The stability of the best electrode is determined by chronopotentiometric and it showed a good stability.     

Partial phosphorization of porous Co–Ni–B for efficient hydrogen evolution electrocatalysis

Design of cost-effective and high-efficient electrocatalysts for hydrogen evolution reaction (HER) is of vital significance for the current renewable energy devices — fuel cells. Herein, we report a facile strategy to prepare partial phosphorization of Co–Ni–B material with porous structure via a water-bath boronizing and subsequent phosphorization process at moderate temperature. The optimal atomic proportion of Co to Ni is investigated via physical and electrochemical characterization. As a result, Co₉–Ni₁–B–P exhibits the best HER activity, which require an lower overpotential of ~192 mV to deliver a current density value of 10 mA cm⁻² and a smaller Tafel slope of 94 mV dec⁻¹ in alkaline media, relative to P-free Co–Ni–B catalysts, Co₉–Ni₁–B–P with other Co: Ni proportion and mono metallic borides The excellent electrocatalytic performance of Co₉–Ni₁–B–P is mainly ascribed to the three-dimensional (3D) porous structure and the coordinate functionalization between the borides and phosphides. This work provides a promising strategy for the exploration of quaternary composites as efficient and cost-effective electrocatalysts for HER.     

Electrochemically assisted synthesis of three-dimensional FeP nanosheets to achieve high electrocatalytic activity for hydrogen evolution reaction

Iron phosphide (FeP) is a promising alternative catalyst for electrocatalytic hydrogen evolution reaction (HER) due to its low price, highly active catalytic sites and long-term anti-acid corrosion. Herein, we report a very facile strategy to fabricate novel FeP nanosheets as a HER electrocatalyst. Three-dimensional interconnected nanosheet structures of Fe₂O₃ (3D Fe₂O₃ NS) were directly exfoliated from metal Fe wires by alternating current (AC) voltage disturbance, and a simple subsequent phosphorization process could easily convert γ-Fe₂O₃ into FeP phase, which also maintained the 3D NS structure. Importantly, increasing the AC voltage resulted in the evolution of iron-containing nanostructures from nanoparticles to 2D nanosheets until the formation of 3D NS structure. Owing to the large specific surface area, enriched active sites and abundant hierarchical porous channels, as-prepared 3D FeP NS has exhibited significantly enhanced electrocatalytic HER activities such as a cathode current density of 10 mA cm⁻² at a small overpotential of 88 mV, low Tafel slope (47.7 mV dec⁻¹) and satisfactory long-term stability in acidic electrolyte. We expect that this simple and green synthetic strategy of transition metal phosphides will provide a promising prospect to innovate nonprecious HER electrocatalysts.     

Fabrication of 0D/1D/2D ZnS–CuS nanodots/GNRs/g-C3N4 heterojunction photocatalyst for efficient photocatalytic overall water splitting

Photocatalytic water splitting has become a significant challenge in modern chemistry. In this process, the rate-determining step is the hydrogen evolution reaction (HER). In the present work, a surface modification approach for graphitic carbon nitride (g-C₃N₄) was applied to improve its photocatalytic HER. 0D ZnS–CuS nanodots were synthesized with the hydrothermal method as a co-catalyst to enhance the capability and stability of water splitting in the presence of visible light irradiation. Also, graphene nanoribbons were synthesized from CNTs unzipping to reduce the energy barrier of HER, improve the HE kinetic, and enhance the catalytic performance of the g-C₃N₄. By using ZnS–CuS/GNRs₍₂₎/g-C₃N₄ photocatalyst, a low onset potential of 130 mV, slight Tafel slope of 41 mV dec^?1, as well as excellent stability of 2000 s was obtained in acidic media. This efficient performance is attributed to the increased visible light absorption level in the proposed photocatalyst and the high stability in electron-hole pairs.     

Fabrication,photoelectrochemical and electrocatalytic activity of 1D linear Co(Ⅱ) and Fe(Ⅲ) TPP-based coordination compounds

Application of transition metal elements in catalysis has become a research hotspot in recent years. Here, two kinds of transition metal-centered HER electrocatalyst of Co(Ⅱ)TPP-based coordination compounds and Fe(Ⅲ)TPP-based coordination compounds are reported. Both of coordination compounds show high photocurrent response and excellent hydrogen evolution activity. The most attraction is that FeTPP-OA/PVP58, FeTPP-PTA/PVP58, FeTPP-OA/PVP1300 and FeTPP-PTA/PVP1300 possess a special surface with a big spine-like cross which is different to the regular pyramid morphology of the other coordination compounds, and these coordination compounds display superior HER performance compare to the other samples. Especially, FeTPP-OA/PVP58 exhibits a low overpotential of 83 mV at the current density of 10 mA cm⁻² and an ultralow Tafel slope of 39 mV dec⁻¹ which is close to the Pt/C (29 mV dec⁻¹). The low charge transfer resistance of 14.4 Ω and high photocurrent of 3 μA under visible light illumination also reveal the outstanding photoelectrochemical property of FeTPP-OA/PVP58. This work provides a novel insight into the design of transition metal-centered HER electrocatalyst with high-efficiency electrocatalytic activity and low cost.     

Ni–Zn nanosheet anchored on rGO as bifunctional electrocatalyst for efficient alkaline water-to-hydrogen conversion via hydrazine electrolysis

Bifunctional Ni-15 at.% Zn/rGO catalyst was fabricated by a two-step electrodeposition to be used for efficient alkaline water-to-hydrogen conversion via hydrazine electrolysis. Experiments show that the as-deposited Ni-15 at.% Zn/rGO nanosheet arrays with porous structure possesses excellent catalytic activity and stability towards both hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR). A small overpotential of 49 mV at 10 mA cm⁻² with a low Tafel slope of 26.3 mV dec⁻¹, and a retention rate of 91.4% after 12 h at 10 mA cm⁻² are observed for Ni-15 at.% Zn/rGO towards HER. Moreover, Ni-15 at.% Zn/rGO also shows an extra-high current density of 1097 mA cm⁻² at 0.6 V vs RHE with a low Tafel slope of 33.5 mV dec⁻¹, and a high durability of 90.5% after 5000 s towards HzOR. Moreover, two-electrode cell was constructed using Ni-15 at.% Zn/rGO as both cathode and anode for HER and HzOR, achieving 100 mA cm⁻² at an ultralow cell voltage of 0.418 V. The above outstanding bifunctional catalytic performance should be attributed to its large ECSA, high electrical conductivity and most importantly, its superaerophobic surface induced by the porous structure with nanosheet arrays.     

Synthesis of functional Ni2P/CC catalyst and the robust performances in hydrogen evolution reaction and nitrate reduction

The non-precious transition metal phosphides (TMPs) as robust and effective hydrogen evolution reaction (HER) catalysts have attracted enormous attention, due to the merits of earth-abundance, low price, desirable stability and high efficiency. However, the conventional preparation process of this kind of catalyst is inconvenient. Herein, we report a facile approach toward the fabrication of nickel phosphide (Ni₂P) assembled on carbon cloth (CC) via the coupling method of electroless plating and low temperature phosphorization. Then, the crystallinity, morphology and chemical component of fabricated self-supporting Ni₂P/CC catalyst employed for the HER process were characterized, and the HER property was successively evaluated in three types of electrolytes (i.e., acidic, neutral and alkaline solutions). The as-prepared Ni₂P/CC catalyst displays a remarkable HER performance, which can be corroborated by the small Tafel slope (b = 50 mV dec⁻¹), high exchange current density (j₀ = 6.6 × 10⁻² mA cm⁻²), acceptable overpotential (119 mV) to attain the current density of 10 mA cm⁻², as well as the superb stability (<5% decay after 24 h potentiostatic test) in 0.5 M H₂SO₄. In addition, it should be noted that the HER process of Ni₂P/CC catalyst can be competent for the reduction of nitrate from the solution, and an efficiency of 63.2% for this nutrient pollutant is achieved.     

Glycerol electrooxidation on Pd,Pt and Au nanoparticles supported on carbon ceramic electrode in alkaline media

In the present study, electrooxidation of glycerol was investigated on Au, Pd and Pt nanoparticles modified carbon ceramic electrode (CCE) by using different electrochemical techniques such as: Cyclic voltammetry (CV), Chronoamperometry (CA), Chronopotentiometry (CP) and Electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were also employed to physicochemical survey of the electrocatalysts. The kinetic parameters of glycerol oxidation, i.e. Tafel slope and activation energy (E_a), were determined on the modified electrodes. The Tafel slopes of 166 mV dec⁻¹ on Pt|CCE, 177 mV dec⁻¹ on Au|CCE and 136 mV dec⁻¹ on Pd|CCE were obtained. The lowest E_a value of 11.2 kJ mol⁻¹ was calculated on Au|CCE. In continuation, the reaction orders with respect to the glycerol and NaOH concentrations on Pd|CCE were found to be 0.27 and 0.87, respectively. The CV, CP and CA results showed remarkable electrocatalytic activity and good poisoning tolerance of Au|CCE for glycerol oxidation.     

Self-supported three-dimensional WP2 (WP) nanosheet arrays for efficient electrocatalytic hydrogen evolution

The development of highly efficient, stable, eco-friendly and low-cost noble-metal-free electrocatalysts is still a great challenge to generate large scale hydrogen fuel from water. In this concern, self-supported WP₂ and WP nanosheet (NS) arrays were prepared through an in-situ solid-phase phosphidation of WO₃ nanosheet arrays on carbon cloth (CC), whereas, different phosphating temperatures of 650 °C, 800 °C for 2 h, has been utilized to attain different WP₂ NS/CC, WP NS/CC catalysts. Remarkably, the electrocatalysts of WP₂ and WP NS arrays exhibit an outstanding hydrogen evolution (HER) performance in acidic environment, with a low overpotential of 140 mV and 175 mV at 10 mA cm⁻², a Tafel slope of 85 mV dec⁻¹ and 103 mV dec⁻¹, respectively. Furthermore, Density Functional Theory (DFT) calculations reveal that the enhanced HER activity of WP₂ catalyst is attributed to the lowered hydrogen adsorption free energy on WP₂ surface, which is much lesser than that on the WP catalyst surface. As a result, WP₂ exhibit superior intrinsic catalytic activity than WP. This study offers a valuable way for the synthesis of highly efficient three-dimensional self-supporting catalytic electrodes, and beneficial for realizing the intrinsic electrocatalytic properties of tungsten phosphide for improved water splitting reactions.     

ZnS,Fe, and P co-doped N enriched carbon derived from MOFs as efficient electrocatalyst for oxygen reduction reaction

Exploring electrocatalysts with low cost and excellent performance for oxygen reduction reaction is still a significant challenge. In this paper, we introduce a novel strategy to fabricate ZnS, Fe, and P co-doped N enriched carbon (ZnFeSP/NC) via the direct carbonization of PVP/ZIF-8 combined with absorption, sulphurization, and phosphorization processes. The as-synthesized ZnFeSP/NC was used as electrocatalyst for oxygen reduction reaction (ORR). We explored the influence of Fe, S, and P elements on the ORR activity of the catalysts. It can be found that ZnS nanoparticles were formed and attached on the surface of the ZnFeSP/NC nanoparticles. α-Fe and P element were well dispersed on ZnFeSP/NC nanoparticles. Fe, S, and P element can highly enhance the ORR activity of the catalysts. Compared to Zn/NC, ZnFe/NC, and ZnFeS/CN, ZnFeSP/NC shows the optimal ORR performance with the half-wave potential of 0.859 V and a current density of 3.33 mA cm⁻² at −0.85 V. Furthermore, ZnFeSP/NC also exhibits excellent long-term operation stability, effectively avoiding any ORR performance decay.     

Mesoporous nickel-sulfide/nickel/N-doped carbon as HER and OER bifunctional electrocatalyst for water electrolysis

The development of non-precious metal-based highly active bi-functional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is critical factor for making water electrolysis a viable process for large-scale industrial applications. In this study, bi-functional water splitting electrocatalysts in the form of nickel-sulfide/nickel nanoparticles integrated into a three-dimensional N-doped porous carbon matrix, are prepared using NaCl as a porous structure-forming template. Microstructures of the catalytic materials are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and N₂ adsorption-desorption analysis. The most active catalyst synthesized in this study exhibits a low HER overpotential of 70 mV at 10 mA cm⁻² and a low Tafel slope of 45 mV dec⁻¹. In OER, the optimized sample performs better than a state-of-the-art RuO₂ catalyst and produces an overpotential of 337 mV at 10 mA cm⁻², lower than that of RuO₂. The newly obtained materials are also used as HER/OER electrocatalysts in a specially assembled two-electrode water splitting cell. The cell demonstrates high activity and good stability in overall water splitting.     

Atomic-scale intercalation of amorphous MoS2 nanoparticles into N-doped carbon as a highly efficient electrocatalyst for hydrogen evolution reaction

The hydrogen evolution reaction (HER) properties of the catalysts are significantly dependent on their microscopic structure. Interfacial engineering at the atomic level is the main approach to design high performance of electrocatalysts. Herein, an interfacial modulation strategy is proposed to fabricate monolayer amorphous MoS₂ nanoparticles with an average of 3.5 nm in diameter stuck in multilayer N-doped carbon (MoS₂/NC), boosting a high HER activity. The amorphous MoS₂ could provide more edge active sites and NC layers endow the fast electron transfer. The XPS, Raman spectra and density functional theory (DFT) calculations reveal that the C–S bond in MoS₂/NC provides the fast electron transfer and decreases H binding energy. Benefiting the unique sandwiched structure, the MoS₂/NC boosts a low overpotential of 152.6 mV at a current density of 10 mA cm⁻², a small Tafel slope of 60.3 mV dec⁻¹, and outstanding long-term stability with 97.3% retention for over 24 h. This strategy provides a new opportunity and development of interfacial engineering for turning intrinsic catalytic activity for water splitting.