Ultrafine Ru nanoparticles derived from few-layered Ti3C2Tx MXene templated MOF for highly efficient alkaline hydrogen evolution

It is meaningful to search high-efficient and inexpensive electrocatalysts for hydrogen evolution reaction (HER) due to the energy crisis and environmental pollution. Here, we report the preparation of ultrafine Ru nanoparticles from a hybrid of ZIF-L(Co) MOF and polydopamine coated few-layered Ti₃C₂T_x MXene (FL-Ti₃C₂T_x). FL-Ti₃C₂T_x is used as a template to grow regular leaf-shaped ZIF-L(Co) nanosheets through the reaction of Co ions anchored on the MXene surface with 2-methylimidazole. The obtained hybrid is then doped with Ru ions through ion exchange between Ru and Co ions, followed by thermal annealing at a temperature of 350 °C in an Ar atmosphere to produce ultrafine Ru nanoparticles. The obtained Ru@ZIF-L(Co)/FL-Ti₃C₂T_x nanocomposite shows outstanding HER performance with a low overpotential of 16.2 mV at a current density of 10 mA cm^?2, a small Tafel slope of 21.0 mV dec^?1 and excellent stability in 1.0 M KOH solution. This work provides a new strategy for the design and synthesis of highly efficient HER catalyst via MOFs with tunable composition and structure.     

Quasi zero-dimensional MoS2 quantum dots decorated 2D Ti3C2Tx MXene as advanced electrocatalysts for hydrogen evolution reaction

Developing advanced noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) is still a great challenge. Herein, a novel HER catalyst with quasi zero-dimensional (0D) MoS₂ quantum dots (QDs) supported on two-dimensional (2D) Ti₃C₂T_x MXene nanosheets is facilely synthesized. The MoS₂ QDs/Ti₃C₂T_x nanohybrid retains the unique layer structure, and the MoS₂ QDs are in situ formed and distributed uniformly. The obtained MoS₂ QDs/Ti₃C₂T_x catalyst exhibits superior electrocatalytic activity due to its excellent conductivity, abundant of active sites exposed and a high percentage of 1T metallic phase (～76%) of MoS₂ QDs. Remarkably, an early HER overpotential of 220 mV at 10 mA cm^?2 and a small Tafel slope of 72 mV dec^?1 of MoS₂ QDs/Ti₃C₂T_x are achieved in 0.5 M H₂SO₄ solution. In addition, the exchange current density of MoS₂ QDs/Ti₃C₂T_x is ～5 times larger compared with pure MoS₂, thus demonstrating an accelerated charge transfer during the electrocatalytic process.     

S-doped multilayer niobium carbide (Nb4C3Tx) electrocatalyst for efficient hydrogen evolution in alkaline solutions

Developing highly efficient and low cost electrocatalysts for hydrogen evolution reaction (HER) is a popular topic for electrocatalytic water splitting to hydrogen technology. Herein, we report a novel heterostructure electrocatalyst prepared by the S-doping multilayer niobium carbide (S-ML-Nb₄C₃T_x) through hydrothermal technique. Compared with pristine ML-Nb₄C₃T_x catalyst, the as prepared electrocatalyst presents remarkable catalytic activity for HER with lower overpotential of 118 mV@10 mA/cm² and a Tafel slope of 104 mV dec^?1 in 1.0 M KOH solution. In addition, the catalyst exhibits a stable electrochemical durability of as long as 24 h in 1.0 M KOH. Efficient HER ability of the S-ML-Nb₄C₃T_x catalyst is mainly attributed to the following points: Firstly, the ML-Nb₄C₃T_x with superior conductivity and stability can effectively avoid the aggregation and oxidation. Secondly, the conversion of fluorine termination groups to –OH by TMAOH treatment can expose more active sites. Further, after the S-doping by hydrothermal reaction, NbS₂ nanoparticles can prevent the ML-Nb₄C₃T_x nanosheets from restacking. As a result, the enlarged interlayer spacing and porous structure of the catalyst are conducive to the charge transfer. In addition, the introduction of NbS₂ nanoparticles on the surface of ML-Nb₄C₃T_x can form heterostructure and subsequently adjust the electronic structure of the catalyst, accelerate the electron transfer, and improve the HER performance. This work presents a new strategy for the designing and preparation of low cost MXene-based catalysts for HER application.     

Construction of Co-decorated 3D nitrogen doped-carbon nanotube/Ti3C2Tx-MXene as efficient hydrogen evolution electrocatalyst

Rational design of transition metal catalysts with robust and durable electrocatalytic activity for hydrogen evolution reactions (HER) is extremely important for renewable energy conversion and storage, as well as water splitting. Heteroatom doping has emerged as a feasible strategy for enhancing electrocatalytic activity. Here, cobalt nanoparticles (Co-NPs) were coated with nitrogen-doped carbon nanotubes (NCNTs) prepared via an in situ growth on accordion-like Ti₃C₂T_x-MXene (Co-NCNT/Ti₃C₂T_x). Such an intriguing structure showed great features: abundant anchoring sites for NCNT in situ growth, intimate integration of Co-NPs and NCNTs, high-speed electron transfer between 1D NCNTs and 2D Ti₃C₂T_x-MXenes, and a large number of effective catalytic active sites. This Co-NCNT/Ti₃C₂T_x hybrid catalyst was demonstrated to possess excellent HER performance with low overpotential (η₁₀, 190 mV), small Tafel slope (78.4 mV dec⁻¹), large electrochemically active surface area, and good long-term stability, thus outperforming many reported electrocatalysts. The present strategy provided a facile route for the design of transition metal HER catalysts with NCNT and MXene.     

Extraordinarily high hydrogen-evolution-reaction activity of corrugated graphene nanosheets derived from biomass rice husks

The metal-free carbonaceous catalysts are one of the promising candidates for efficient electrocatalytic hydrogen production. Aiming at demonstrating the high electrocatalytic activity of the hydrogen evolution reaction (HER), we synthesized the biomass rice husk-derived corrugated graphene (RH-CG) nanosheets via the KOH activation. The 700 °C-activated RH-CG nanosheets exhibited the large specific surface area as well as the high electrical conductivity. When using the RH-CG nanosheets as a HER electrocatalyst in 0.5 M H₂SO₄, the excellent HER activities with a small overpotential (9 mV at 10 mA/cm²) and a small Tafel slope (31 mV/dec) were achieved. The results provide a new strategy for materializing the superb biomass-derived electrocatalyst for highly efficient hydrogen production.     

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.     

NiFe LDH/Ti3C2Tx/nickel foam as a binder-free electrode with enhanced oxygen evolution reaction performance

In this work, NiFe LDH/Ti₃C₂T_x/Nickel foam (NF) was successfully prepared as a binder-free electrode by depositing NiFe layered double hydroxide (LDH) nanosheets on Ti₃C₂T_x/NF substrate through electrodeposition approach. The strong electrostatic interactions between the negatively charged surface of MXene and positively charged NF substrate enabled the direct growth of NiFe LDH nanosheets on Ti₃C₂T_x/NF substrate. As a result, the as-prepared NiFe LDH/Ti₃C₂T_x/NF electrode exhibited an excellent OER performance, fast catalytic reaction kinetics and good chemical stability. Its overpotential reached 200 mV at a current density of 10 mA cm^?2, and the cycling tests suggested a good cycling stability.     

Mo-chelate strategy for synthesizing ultrasmall Mo2C nanoparticles embedded in carbon nanosheets for efficient hydrogen evolution

Production of hydrogen from electrochemical water splitting has been regarded as one of the most economic and sustainable techniques for green fuel production. It is significant and challengeable to develop highly efficient and low cost noble metal-free electrocatalysts. Presently, molybdenum-based electrocatalysts were regarded as potential alternatives for the hydrogen evolution reaction (HER). Here, the well-dispersed and ultrasmall Mo₂C nanoparticles (NPs) anchored on 2D carbon nanosheets were synthesized by designing chelate precursor and following pyrolysis, which was proved to be an effective approach for preparing carbon-loaded Mo₂C NPs. The as-obtained Mo₂C/C material exhibits an outstanding activity and stability in hydrogen evolution reaction (HER). It needs an overpotential of 147 mV to drive 10 mA cm⁻² and Tafel slope is 64.2 mV dec⁻¹ in alkaline medium, implying that Mo₂C/C material will be a potential noble metal-free electrocatalyst for HER. The design of Mo-chelate precursor is a feasible route to synthesize ultrafine Mo₂C and it can provide a reference for synthesizing other nanoparticles and hindering particle coalescence at high preparation temperature.     

Engineering of molybdenum sulfide nanostructures towards efficient electrocatalytic hydrogen evolution

Water splitting is an appealing way of producing hydrogen fuel, which requires efficient and affordable electrode materials to make the overall process viable. In the last couple years, abundant transition metals (and their compounds and hybrids) attracted ever-growing attention as the alternatives of noble metals. Particularly the layered transition metal dichalcogenide (TMDs) are interesting with their stability and promising electrocatalytic performance for hydrogen evolution reaction (HER). However, the neat TMDs are often poor in terms of the abundance of catalytically active sites and electrical conductivity, which limit their application potential significantly. Herein, as a proof-of-concept, we report on the design of a high-performance electrocatalyst system formed by the decoration of ultrasmall molybdenum sulfide (MoS₂) nanosheets on carbon nanotubes (CNTs). The ultrasmall MoS₂ nanosheets provide distorted lattice, confined size and rich defects, which endows the resulting electrocatalysts (MoS₂/CNT) with abundant active sites. The CNTs, on the other hand, serve as the conductive net for ensuring electrocatalytic performance. As a result, the hybrid electrocatalyst exhibits excellent electrocatalytic performance for HER, achieving a large current density of 100 mA cm⁻² at overpotential of only 281 mV and a small Tafel slope of 43.6 mV dec⁻¹ along with a decent stability. Our results are of high interest for electrocatalyst technologists as well as hydrogen fuel researchers.     

Bottom-up construction of three-dimensional porous MXene/nitrogen-doped graphene architectures as efficient hydrogen evolution electrocatalysts

The exploration of highly-active non-platinum electrocatalysts with low-cost has been regarded as a crucial way to alleviate the major bottleneck in electrocatalytic hydrogen evolution reaction (HER) technology. Herein, we demonstrate the bottom-up construction of three-dimensional (3D) hybrid architectures built from Ti₃C₂T_x MXene and nitrogen-doped graphene nanosheets (MX/NG) through a facile and cost-effective co-assembly approach. The as-derived MX/NG architectures are endowed with a number of distinctive structural advantages, such as large specific surface areas, 3D cross-linked porous frameworks, ultrathin walls, optimized electronic structures, and good electron conductivity. As a result, exceptional HER performances with a relatively low onset potential, a small Tafel slope, and reliable long-term stability are achieved on the optimized MX/NG electrode, markedly outperforming those of bare Ti₃C₂T_x and NG electrodes.     

Facile synthesis of cobalt modified 2D titanium carbide with enhanced hydrogen evolution performance in alkaline media

2D transition metal carbides, nitrides and carbonitrides, namely the MXenes, attract more and more attentions due to their unique properties. Here, we report a simple one-step molten salt etching method to prepare Co modified MXene hybrid (Ti₃C₂T_x:Co) by the reaction of Ti₃AlC₂ with Lewis acid CoCl₂ at 750 °C. Most of Co atoms aggregates in the interlayered space of Ti₃C₂T_x. Benefitting from the improved electron charge transfer efficiency and increased active sites, the sulfuric acid treated Ti₃C₂T_x:Co-12h hybrid exhibits excellent electrocatalytical activity for hydrogen evolution reaction in alkaline media, delivering a current density of 10 mA cm⁻² at an overpotential of 103.6 mV, which is lower than most noble metal free MXene based electrocatalysts. The results illustrate that the proposed method is very facile and useful to incorporate mid-to-late transition metals into the MXene phase to prepare MXene based HER electrocatalysts.     

Accelerate the alkaline hydrogen evolution reaction of the heterostructural Ni2P@Ni(OH)2/NF by dispersing a trifle of Ru on the surface

Electrocatalytic water splitting for hydrogen production plays a vital role in the development of new energy field, but there is still a lack of low-content precious metal or cost-effective non-noble metal catalysts for the hydrogen evolution reaction (HER). Therefore, how to develop the catalysts with a smaller amount of precious metal to achieve higher performance is still a major challenge. Herein, we have fabricated Ru–Ni₂P@Ni(OH)₂/NF-2 heterostructure by phosphating Ni(OH)₂/NF and then anchoring Ru on the surface through wet chemical strategy. Benefiting from its optimal ΔG_H1 and synergistic effect, this Ru–Ni₂P@Ni(OH)₂/NF-2 catalyst shows superior electrocatalytic HER kinetics in alkaline electrolyte. A small overpotential of 31 mV is needed for this electrocatalyst to obtain the current densities of 10 mA cm^?2 with remarkable durability over 24 h. This work provides a new strategy for the preparation of effective HER electrocatalyst with a low precious metal content.     

Bismuth tungstate-anchored PEDOT: PSS materials for high performance HER electrocatalyst

Bismuth tungstate anchored PEDOT: PSS (BiW@PEPS) electrocatalyst was prepared via hydrothermal and ultrasonication methods successively. The synergetic effects of bismuth tungstate with PEDOT: PSS conducting polymer showed excellent electrocatalytic performance of hydrogen evolution reactions (HER) in alkaline conditions. When compared with pristine bismuth tungstate, the BiW@PEPS exhibited an enhanced electrocatalytic activity with a lower overpotential of 361 mV at 10 mA cm⁻², small Tafel slope of 106 mV/dec and enduring stability in 1 M KOH electrolyte. The enhanced electrocatalytic performance of the BiW@PEPS proved to be a beneficial electrocatalyst to the high-cost platinum-based materials in hydrogen production applications.     

Efficient CoMoRu0.25Ox/NF nanoplate architectures for overall electrochemical water splitting

The development of inexpensive electrocatalysts with excellent electrocatalytic activity for the hydrogen and oxygen evolution reactions (HER and OER, respectively) has been challenging. In this study, we synthesized cobalt molybdenum ruthenium oxide with porous, loosely-assembled nanoplate morphology. The CoMoRu_0.25O_x/NF electrocatalyst exhibited the highest electrocatalytic activity, requiring overpotentials of 230 and 78 mV for the OER and HER, respectively, to attain a current density of 10 mA cm^?2; moreover, its long-term stability was outstanding. The electrocatalyst required a cell voltage of only 1.51 V for overall water splitting in an alkaline medium, which was lower than that required by many CoMo-based catalysts.     

MoS2/Mo2TiC2Tx supported Pd nanoparticles as an efficient electrocatalyst for hydrogen evolution reaction in both acidic and alkaline media

Development of electrocatalytic hydrogen production technology is the key to solving environmental and energy problems. Two-dimensional material Mo₂TiC₂T_x (T_x = –OH, –F) has shown great potential in electrocatalytic hydrogen evolution because of its excellent conductivity and hydrophilicity. However, due to the lack of sufficient active sites of Mo₂TiC₂T_x itself, its practical applications in electrocatalytic hydrogen evolution are limited. In this work, a highly-efficient hydrogen evolution electrocatalyst, namely Pd@MoS₂/Mo₂TiC₂T_x, is prepared through a simple pyrolysis method. In such a composite, the MoS₂ nanoflowers hybridized with the ammonia-treated Mo₂TiC₂T_x (MoS₂/Mo₂TiC₂T_x) are used as a substrate for loading a small number of Pd nanoparticles (4.27 at.%). Notably, the introduction of Pd nanoparticles into MoS₂/Mo₂TiC₂T_x provides abundant active sites for the hydrogen evolution reaction, improves the conductivity of the electrocatalyst, speeds up the adsorption and desorption of hydrogen, and induces a synergistic effect with the MoS₂. As a result, the Pd@MoS₂/Mo₂TiC₂T_x catalyst exhibits excellent electrocatalytic performance and remarkable stability in both acidic and alkaline media. In a 0.5 mol/L H₂SO₄ electrolyte, the overpotential of Pd@MoS₂/Mo₂TiC₂T_x was 92 mV with a Tafel slope of 60 mV/dec at a current density of 10 mA/cm². Meanwhile, the catalyst displayed an overpotential of 100 mV associated with a Tafel slope of 80 mV/dec at the current density of 10 mA/cm² in a 1 mol/L KOH electrolyte. This work shows the great potential of using Mo₂TiC₂T_x-based material in the field of electrocatalysis.     

Hierarchical nanohybrid of CuS/NiS2/Ti3C2 heterostructure with boosting charge transfer for efficient photocatalytic hydrogen evolution

Fabricating heterostructure photocatalysts with co-catalysts can improve the separation and transfer of photo-induced electrons and holes for photocatalysis reactions. Herein, Ti₃C₂T_x nanosheets are obtained by chemical etching via the hydrothermal route and serve as a template for growing photocatalysts. NiS₂ nanoparticles and CuS nanoneedles are deposited sequentially on the surface of Ti₃C₂T_x nanosheets to form “Type II” CuS/NiS₂/Ti₃C₂T_x hierarchical heterostructure via the solvothermal method. The enormous nanoneedles morphology provides enlarged active sites for the photocatalytic processes. The fabricated CuS/NiS₂/Ti₃C₂T_x heterostructure delivers an increased hydrogen generation rate of 32.66 mmol g⁻¹ h⁻¹, which is higher than that of pure CuS (2.38 folds), NiS₂ (1.93 folds), and NiS₂/Ti₃C₂T_x (1.71 folds). CuS/NiS₂/Ti₃C₂T_x heterostructure also performs a superior hydrogen evolution retention of 97.7% after 4 cycles (one cycle lasts 4 h), implying its decent structural stability and light corrosion resistance. The reasons are ascribed to the constructed “Type II” heterostructure of CuS/NiS₂ with higher active sites, improved conductivity, and efficient separation of electrons and holes. DFT calculation and Mott-Schottky plots results elucidate the formation mechanism of CuS/NiS₂/Ti₃C₂T_x “Type II” structure. CuS/NiS₂/Ti₃C₂T_x heterostructure also obtains a reduced bandgap with increased light absorption. The van der Waals force between 2D materials enhances the transfer of photo-generated electrons. This work demonstrates that designing hierarchical co-catalyst heterostructure without non-noble can effectively promote water splitting in the solar-to-chemical system.     

Ru–MoS2@PPy hollow nanowire as an ultra-stable catalyst for alkaline hydrogen evolution reaction

Electrocatalytic hydrogen evolution reaction (HER) is one of the green and effective method to produce clean hydrogen energy. However, the development of non-Pt HER catalysts with excellent catalytic activity and long-term stability still remains a great challenge. Herein, a vertically aligned core-shell structure material with hollow polypyrrole (PPy) nanowire as a core and Ru-doped MoS₂ (Ru–MoS₂) nanosheets as a shell is firstly reported as a highly efficient and ultra-stable catalyst for HER in alkaline solutions. Results indicate that Ru–MoS₂@PPy catalyst demands a low overpotential of 37 mV at 10 mA cm^?2. In addition, the overpotential at 100 mA cm^?2 is 157 mV and it is almost unchanged after 40,000 cyclic voltammetry cycles. The existence of PPy core not only ensures the vertical growth of MoS₂ nanosheets to expose more edge sites, but also promotes the rapid transfer of electrons, contributing to the improvement of catalytic activity. More importantly, the strong interface interaction between MoS₂ and PPy prevents the collapse of the vertical structure of MoS₂ sheets in the electrocatalytic process and greatly enhances the stability of catalysts, which offers an effective strategy to design and synthesize the HER catalysts with superior catalytic stability.     

Chlorophyll derivatives/MXene hybrids for photocatalytic hydrogen evolution: Dependence of performance on the central coordinating metals

Development of efficient photocatalytic hydrogen evolution reaction (HER) with illumination of visible light is challenging. In this work, five chlorophyll derivatives (M-Chls; M = H₂/Cu/Ni/Co/Zn) with different central ions in its cyclic tetrapyrrole ring including free base, copper, nickel, cobalt, and zinc were synthesized and employed as the effective visible-light harvester for efficient HER. In addition, two-dimensional (2D) noble metal-free co-catalyst Ti₃C₂T_x MXene was used as an excellent electron capturer due to its outstanding conductivity property. These M-Chls are modified on the surface of Ti₃C₂T_x MXene with 2D accordion-like morphology by means of a simple deposition process to form noble metal-free Chl/Ti₃C₂T_x-based photocatalysts for HER. It is found that the best HER performance as high as 49 μmol/h/g_cat was achieved with the Co-Chl@Ti₃C₂T_x hybrid, which was much higher than those of other M-Chl@Ti₃C₂T_x composites. This research provides a specific way to synthesize low-cost and environmentally friendly natural Chls for developing highly efficient photocatalytic HER through molecular engineering.     

Molten salt assisted to synthesize molybdenum–ruthenium boride for hydrogen generation in wide pH range

Developing a highly-efficient electrocatalyst for hydrogen evolution reaction (HER) is a necessary step for hydrogen energy production. In this work, molybdenum-ruthenium boride (Mo–Ru–B) electrocatalyst is synthesized with the assistance of the molten salt method. The introduced Ru–B plays a key role in enhancing the electrocatalytic activity. Then, the prepared Mo–Ru–B exhibits highly active in alkaline, acidic, neutral and alkaline seawater with overpotentials of 50 mV, 48 mV, 109 mV, and 108 mV to reach 10 mA cm⁻². Moreover, the synthesized Mo–Ru–B also exhibits excellent stability in various applied electrolytes. The work provides a new approach to the design of stable and high-performance metal boride based electrocatalysts.     

Self-standing and efficient bifunctional electrocatalyst for overall water splitting under alkaline media enabled by Mo1-xCoxS2 nanosheets anchored on carbon fiber paper

The layered MoS₂ nanostructures have been widely used in the electrochemical hydrogen evolution reaction (HER), but rarely applied in overall water splitting application for their ignorable oxygen evolution reaction (OER) activity. To address this issue, a novel self-standing and bifunctional electrocatalyst, consisting of Co-doped MoS₂ nanosheets anchored on carbon fiber paper, has been prepared via hydrothermal method. Taking advantage of conductive substrate of carbon fiber paper, sufficient-exposed active edges of MoS₂ sheets, and metallic character caused by Co-doping, our electrode exhibits high-efficient bifunctional activities for the overall water splitting in alkaline electrolyte (1 M KOH), which can produce a current density of 20 mA cm⁻² at an overpotential of 197 mV for HER and 235 mV for OER.