Synthesis of ultrafine ruthenium phosphide nanoparticles and nitrogen/phosphorus dual-doped carbon hybrids as advanced electrocatalysts for all-pH hydrogen evolution reaction

Pt-group metal phosphides are widely utilized as efficient electrocatalysts for hydrogen evolution reaction (HER), whereas most of the synthetic strategies are complicated, dangerous, and toxic with the use of large amount of nitrogen (N) and/or phosphorus (P) sources. Here, we report the synthesis of ruthenium phosphide nanoparticles (NPs) confined into N/P dual-doped carbon by pyrolyzing self-prepared ruthenium-organophosphine complex using 1,3,5-triaza-7-phosphadamantane (PTA) as the ligand and N/P sources. The achieved S–RuP₂/NPC displayed excellent electrocatalytic activity (overpotentials of 19, 37, and 49 mV in alkaline, neutral, and acidic media, respectively, at 10 mA cm⁻²) toward HER at all pH ranges. The high performance of S–RuP₂/NPC must be ascribed to the homogeneously distributed and P-rich RuP₂ NPs with the diameter of 3.29 nm on the NPC surface, which can considerably improve the atom utilization for HER. The present synthetic strategy not only avoids the use of additional N/P sources but also the generation of flammable and toxic PH₃ gas. This synthetic strategy can be extended to prepare other traditional metal phosphides for electrocatalytic applications.     

Ru/MoO2 decorated on CNT networks as an efficient electrocatalyst for boosting hydrogen evolution reaction

Generally, electrochemical hydrogen evolution reaction (HER) is hampered by slow kinetics and low round-trip efficiency. Electrocatalysts with a hierarchical structure and large surface area are expected to overcome these problems. Herein, we prepared a Ru/MoO₂/carbon nanotubes (RMC) hybrid with a hierarchical structure by a convenient solid-phase reaction (SPR) method, and studied the electrochemical activity for HER. After annealing as-prepared RuO₂/MoO₂/carbon nanotubes (ROMC) precursor in a tubular furnace under Ar atmosphere, RuO₂ and MoS₂ were in-situ transformed into Ru metal and MoO₂ phase by the redox SPR. Through various tests, we have confirmed that the new formed Ru metal and MoO₂ phase are combined and uniformly coated on the outer surface of CNTs. Interestingly, the RMC-500 exhibits the best HER performance with a low overpotential of 16 mV at l0 mA cm^?2, small Tafel slope of 45 mV dec^?1, higher electrochemical active surface area, and long-time durability in alkaline electrolyte.     

Multilevel N-doped carbon nanotube/graphene supported cobalt phosphide nanoparticles for electrocatalytic hydrogen evolution reaction

Electrochemical water splitting plays an important role in alternative energy studies, since it is highly efficient and environment-friendly. Accordingly, it is an ideal way of providing alternative to meet the urgent need of finding sustainable and clean energy. This study presents the fabrication of CoP attached on multilevel N-doped CNT/graphene (CoP–CNT/NG) hybrids. The multilevel carbon structure can enhance electrical conductivity efficiently and increase the reaction active area immensely. The obtained electrocatalyst exhibits great electronic conductivity (17.8 s cm⁻¹) and HER activity with low overpotential (155 mV at 10 mA cm⁻²), low Tafel slope (69.1 mV dec⁻¹) in 0.5 M H₂SO₄. In addition, the CoP–CNT/NG displays prominent electrochemical durability after 18 h.     

Efficient and scalable preparation of MoS2 nanosheet/carbon nanotube composites for hydrogen evolution reaction

An efficient and scalable method combining ball-milling and liquid-phase exfoliation was used to prepare MoS₂ nanosheets. Ammonium bicarbonate as an exfoliation aid could accelerate the delamination and pulverization of bulk MoS₂ during preparation. The ball-milled MoS₂ was further exfoliated by sonication (S–MoS₂NS) or high-speed shear-exfoliation (H–MoS₂NS) to obtain MoS₂ nanosheets dispersion with high concentration. Moreover, MoS₂ quantum dots were also obtained by prolonging sonication time (S–MoS₂QS). Most of S–MoS₂NS and H–MoS₂NS have lateral dimensions less than 150 nm. The S–MoS₂QS size concentrates at around 5 nm. The H–MoS₂NS mixed with aminated multi-walled carbon nanotubes (MWCNT) could form H–MoS₂NS/MWCNT composites with a good conductive network, and was used as a hydrogen evolution reaction (HER) catalyst. The H–MoS₂NS/MWCNT composites containing 56 wt% H–MoS₂NS exhibited a favorable HER activity with a low overpotential of 284 mV at 10 mA/cm², a Tafel slope of 97 mV/dec and good stability in acid medium.     

Novel one-step synthesis of nickel encapsulated carbon nanotubes as efficient electrocatalyst for hydrogen evolution reaction

In this work, we report the synthesis of Ni nanoparticles encapsulated in carbon nanotubes (CNTs) by a facile and novel one-step pyrolysis method which are obtained from fumaric acid and nickel acetate as carbon and nickel sources respectively. The synthesized Ni encapsulated CNTs were characterized by various methods and were confirmed to possess large surface areas and numerous mesopores, they were applied as non-precious metal electrocatalyst for HER in 1 M KOH solution. The results show that the Ni encapsulated carbon nanotubes synthesized at 650 °C exhibited the best catalytic activity and stability with the smallest Tafel slope of 102 mV dec⁻¹, an onset potential of 110 mV and overpotential of 266 mV to achieve a current density of −10 mA cm⁻².     

High-temperature-treated multiwall carbon nanotubes for hydrogen evolution reaction

We investigated the hydrogen evolution reaction (HER) properties of multi-wall carbon nanotubes (MWCNTs) treated at extremely high temperature (2600 °C). The heat treatment not only improves the crystallinity of the MWCNTs, but also reduces the carbon-oxygen (CO) bonding as it is replaced by the defect-carbon (sp³ and CH) bonding. These modifications in the heat treated MWCNT structure lead to the increase of electrochemical charge transfer. The heat treatment of MWCNTs in the composite with Pt (MWCNT-Pt composite) further facilitates electrocatalysis. The MWCNTs-Pt composite shows strong enhancement in the HER performance with an onset of overpotential of ?0.04 V vs reversible hydrogen electrode and a Tafel slope of 10.9 mV/decade. This performance is indeed better than that of Pt, which is the best working material for HER.     

CoS2 with carbon shell for efficient hydrogen evolution reaction

In this study, we demonstrated the active electrocatalysts of CoS₂ coated by N-doped carbon microspheres, CoS₂@NHCs-x (x = 600, 700, 800, and 900; x is pyrolysis temperature). Results show that the obtained electrocatalyst has good catalytic activity and cyclic stability for the reaction of hydrogen evolution (HER) when the pyrolysis temperature is 800 °C. At a current density of 10 mA cm⁻², the overpotential of CoS₂@NHCs-800 was only 98 mV in 0.5 M H₂SO₄, and 118 mV in 1 M KOH, respectively. In addition, CoS₂@NHCs-800 also revealed excellent electrochemical stability, with only 32.7% performance degradation after continuous reaction in 0.5 M H₂SO₄ for 20 h, and the later current density almost no longer deceased with time as the reaction process stabilized. The excellent HER catalytic performance of CoS₂@NHCs-800 is mainly attributed to the rich active sites of CoS₂, the unique porous core-shell structure, and the enhanced conductivity of the carbon carrier caused by N and S co-doping. This work opens up an opportunity for advanced CoS₂-based electrocatalysts for HER.     

Carbon supported nickel phosphide as efficient electrocatalyst for hydrogen and oxygen evolution reactions

Hydrogen production through water splitting is an efficient and green technology for fulfilling future energy demands. Carbon nanotubes (CNT) supported Ni₂P has been synthesized through a simpler hydrothermal method. Ni₂P/CNT has been employed as efficient electrocatalysts for hydrogen and oxygen evolution reactions in acidic and alkaline media respectively. The electrocatalyst has exhibited low overpotential of 137 and 360 mV for hydrogen and oxygen evolution reactions respectively at 10 mA cm^?2. Lower Tafel slopes, improved electrochemical active surface area, enhanced stability have also been observed. Advantages of carbon support in terms of activity and stability have been described by comparing with unsupported electrocatalyst.     

Thermally reduced graphite oxide/carbon nanotubes supported molybdenum disulfide as catalysts for hydrogen evolution reaction

We report an efficient molybdenum disulfide (MoS₂) supported by thermally reduced graphite oxide and carbon nanotubes (TRGO-CNT) for hydrogen evolution reaction. The TRGO-CNT-MoS₂ composite is successfully prepared by a simple sonication process, exhibiting excellent catalytic activity of the hydrogen evolution reaction (HER) with a low overpotential of −0.14 V, which is much lower compared to that of MoS₂, CNT-MoS₂ and TRGO-MoS₂, respectively. TRGO-CNT-MoS₂ also exhibits high stability even after 1000 cycles and strong durability after 48 h. The high HER performance of TRGO-CNT-MoS₂ attributes to a synergic effect of thermal reduced GO and CNT that support MoS₂ due to significant decrease of electrochemical impedance and reliable supporting material for the efficient HER.     

Silicon monoxide assisted synthesis of Ru modified carbon nanocomposites as high mass activity electrocatalysts for hydrogen evolution

Extremely low content of Ruthenium (Ru) nanoparticles were loaded on the carbon black (Ru/C) via reducing Ru ions with silicon monoxide. The obtained Ru/C nanocomposites exhibit an exciting electrochemical catalytic activity for hydrogen evolution reaction (HER) in the oxygen-free 0.5 M H₂SO₄ medium. The optical one (Ru/C-2) with a low Ru amount of 2.34% shows higher activity than previously reported Ru-based catalysts. The overpotential at 10 mA cm⁻² is 114 mV and the Tafel slope is 67 mV·dec⁻¹. Ru/C-2 catalyst also has good stability. The overpotential that afford the current density of 10 mA cm⁻² of 20 wt% Pt/C increased 92 mV while that of Ru/C-2 only increased 50 mV after a 30,000 s chronopotentiometry test. Furthermore, the mass activity of Ru/C-2 catalyst is even better than that of the commercial 20 wt% Pt/C when the overpotential is larger than 0.18 V. This silicon monoxide-mediated strategy may open a new way for the fabrication of high performance electrocatalysts.     

In-situ anion exchange synthesis of copper selenide electrode as electrocatalyst for hydrogen evolution reaction

Efficient and robust Earth-abundant catalysts for hydrogen evolution reaction (HER) is one of the key components for clean energy technologies aimed at reducing future carbon emissions. Here, an in-situ anion exchange approach to prepare hierarchical nanostructures consisting of ultrathin Cu_2-xSe nanosheet is reported. With the aid of the selenylation process and the hierarchical ultrathin nanostructure, the nanostructured Cu_2-xSe/Cu foam electrode achieved considerably enhanced HER performance with a large geometric current density of ?100 mA cm^?2 at a small overpotential of 313 mV and outstanding long-term operational stability. Significant improvement of electrocatalytic activity for Cu_2-xSe catalyst could be attributed to the promoted mass diffusion/transfer properties, which results from its special structural feature. Meanwhile, the overpotential associated with the catalyst/substrate interface could be effectively eliminated due to the self-supported construction. We believe that this work will lead towards the further development of Cu-based chalcogenides for applications in electrocatalysis and energy conversion.     

Electrochemical behaviour of single walled carbon nanotubes – Hydrogen storage and hydrogen evolution reaction

The electrochemical behaviour of single walled carbon nanotubes (SWCNT) related to the mechanism involved in the hydrogen electrode reaction applying electrochemical and spectroscopic techniques is studied. Cyclic voltammetry applied to electrodes containing different percentages of SWCNT demonstrates that this material can behave as efficient capacitor and that the hydrogen electrode reaction develops through the H-electrosorption followed by the formation of molecular H₂ and its evolution. Also, SWCNT are able to storage hydrogen within their porous structure. This is confirmed through the galvanostatic charge and discharge experiments. Electrochemical impedance spectroscopy allowed calculating the real area that takes part in the electrode reaction and the main and valuable conclusion is that the hydrogen electrode reaction consists of a simple charge transfer reaction and that the H adatom relaxation or diffusion processes can be disregarded. Furthermore, a model proposed for their structure which was validated through impedance experiments confirms those conclusions. Results of Raman spectra allowed identifying the nature of the electrodes confirming that after purification the material is composed of single walled carbon nanotubes.     

Tailoring CoNi alloy embedded carbon nano-fibers by thiourea for enhanced hydrogen evolution reaction

Toward the evolution of structure and composition of transition-metal based catalysts for hydrogen evolution reaction (HER), thiourea is utilized to tailor the size and distribution of CoNi alloy nanoparticles embedded in electrospinning carbon nanofibers (CoNi@CNFs). When adding appreciate dose of thiourea in the electrospinning precursor, the average grain size of CoNi nanoparticles reduces from 19.4 to 10.2 nm by the steric barrier effect of thiourea. Meanwhile, thiourea controls the favorable growth of CoNi on the surface of CoNi@CNFs. The surface CoNi alloy content increases from 25.1 to 34.6 wt %. The refining and well-dispersed CoNi nanoparticles improve the graphitization degree of carbon substrates. Furthermore, Thiourea provides S doping in CoNi alloy as well as the S, N doping in carbon substrates. The evolution of the structure and composition of CoNi@CNFs catalyst boosts the electronical performances by effectively modulating the electronic structure of the active sites, enlarge the exposure of active sites, and facilitate the electron transfer and mass diffusion. As a result, the optimized CoNi@CNFs (Thu-1.0) shows remarkable low overpotential (116 mV, 10 mA cm^?2@1.0 mol KOH), outstanding hydrogen production rate (24.5 μmol/h, 20 mA cm^?2@1.0 mol KOH), and superior stability (7.8% overpotential enlargement after 5000 continuous linear voltammetric cycles), when used as a catalyst material for HER application.     

Electrocatalytic hydrogen evolution on iron-cobalt nanoparticles encapsulated in nitrogenated carbon nanotube

Using low-cost nonprecious metals to replace Pt as hydrogen evolution reaction (HER) electrocatalyst is promising, but still limited by their efficiency and stability. Herein, with low-cost dicyandiamide and metal salts as precursor, FeCo alloy nanoparticles encapsulated in nitrogenated carbon nanotubes (FeCo-NCNTs) were facially synthesized as efficient HER electrocatalyst. Addition of iron as second element, though not facilitating the formation of carbon nanotube, was utilized to improve the physicochemical properties of metals. Via optimizing the atomic molar ratios of Fe/Co nanoparticles, the optimal Fe_0.4Co_0.6-NCNTs with thin carbon shell (c.a. 5–10 layer) and equally distribution of embedded alloy nanoparticles was found with outstanding HER activity. To achieve a current density of 10 mA cm⁻², only overpotential of 50 mV, 157 mV and 202 mV were needed in acidic (0.5 M H₂SO₄), alkaline (1 M KOH), and neutral solutions. Its higher electrochemically active surface areas and lower electron transfer resistance may contribute to the excellent electrocatalytic HER. Furthermore, the illustrated current density slightly changed over 20 h, suggesting excellent stability. Hence, the present method provides cost-effective, high efficiency, and stable materials in developing the sustainable energy conversion systems.     

Shaddock peel derived nitrogen and phosphorus dual-doped hierarchical porous carbons as high-performance catalysts for oxygen reduction reaction

Oxygen reduction reaction (ORR) plays a key role in the application of fuel cells. Here, we used shaddock peel to fabricate a set of N, P dual-doped hierarchical porous carbons, abbreviated as NPSPs, where the carbons were carbonized, activated and dual-doped via a simple one-step pyrolyzation. Contrast results indicate the contents of pyridinic-N, graphitic-N and P–C species increase with the rising of temperatures, and the temperature also affects the degree of graphitization, surface area, morphology, thus influences the ORR performance. More importantly, the NPSP-900 demonstrates an outstanding ORR activity with a comparable half-wave potential (0.83 V vs. RHE) and higher current density with respect to commercial Pt/C, following 4e transfer pathway. Our work illustrates that NPSP-900 is a promising cathode for fuel cells because of its simple preparation, waste utilization, excellent ORR performance, good methanol tolerance and superior stability.     

Spatially localized fabrication of uniform Rh nanoclusters on nanosheet-assembled hierarchical carbon architectures as excellent electrocatalysts for boosting alkaline hydrogen evolution

Construction of homogenously distributed and ultrafine Rh nanoclusters (NCs) anchored on suitable support with low loading toward hydrogen evolution reaction (HER) is paramount but remains challenging. Here, we developed a space confinement-assisted strategy for the construction of highly dispersed and ultrasmall Rh NCs supported on 3D nanosheet-assembled hierarchical carbon architectures (NHCAs) as advanced electrocatalysts for alkaline HER. Benefiting from the abundant and ultrasmall micro/mesopores of NHCAs, uniformly dispersed Rh NCs with diameters of 1.83 nm were embedded in NHCAs without the aid of surface capping agents. The resultant Rh NCs/NHCAs exhibited excellent electrochemical HER activity with low overpotentials of 7 and 48 mV at 10 and 100 mA cm⁻² current densities in basic solution, respectively, superior than most of the previous developed electrocatalysts. The surface-clean and ultrafine Rh NCs with high dispersity on the NHCAs surface could provide abundant surface-active sites and resulted in the high performance of Rh NCs/NHCAs for HER. The present study may offer a novel yet convenient pathway to synthesize highly dispersed and catalytically active supported noble metal electrocatalyst for catalytic applications.     

Hierarchical NiMo alloy microtubes on nickel foam as an efficient electrocatalyst for hydrogen evolution reaction

Developing efficient, non-noble electrocatalysts for hydrogen evolution reaction (HER) is of high significance for future energy supplement, but challenging. NiMo alloy is a non-noble-metal-based efficient catalyst for HER due to its appropriate hydrogen binding energy and excellent alkali corrosion resistance. Herein, for the first time, we report the preparation of radially aligned NiMo alloy microtubes on Ni foam (NiMo MT/NF). The synthesized NiMo alloy catalyst was composed of the Ni₁₀Mo phase; notably, this hierarchically structured material possessed abundant active sites and a high surface area, and exhibited efficient electronic transport properties. The NiMo MT/NF electrode exhibited a low overpotential of 119 mV at 10 mA/cm² in a base solution, which was 50 mV less than that of NiMo alloy nanoparticles on NF (169 mV).     

Co/Mo2C composites for efficient hydrogen and oxygen evolution reaction

Non-precious transition metal electrocatalysts with high catalytic performance and low cost enable the scalable and sustainable production of hydrogen energy through water splitting. In this work, based on the polymerization of CoMoO₄ nanorods and pyrrole monomer, a heterointerface of carbon-wrapped and Co/Mo₂C composites are obtained by thermal pyrolysis method. Co/Mo₂C composites show considerable performance for both hydrogen and oxygen evolution in alkaline media. In alkaline media, Co/Mo₂C composites show a small overpotential, low Tafel slope, and excellent stability for water splitting. Co/Mo₂C exhibits a small overpotential of 157 mV for hydrogen evolution reaction and 366 mV for oxygen evolution reaction at current density of 10 mA cm⁻², as well as a low Tafel slope of 109.2 mV dec⁻¹ and 59.1 mV dec⁻¹ for hydrogen evolution reaction and oxygen evolution reaction, respectively. Co/Mo₂C composites also exhibit an excellent stability, retaining 94% and 93% of initial current value for hydrogen evolution reaction and oxygen evolution reaction after 45,000 s, respectively. Overall water splitting via two-electrode water indicates Co/Mo₂C can hold 91% of its initial current after 40,000 s in 1 M KOH.     

Fabrication of phosphorus-mediated MoS2 nanosheets on carbon cloth for enhanced hydrogen evolution reaction

Molybdenum sulfide (MoS₂) as a graphene-like sheet material has attracted wide attention owing to the potential for hydrogen evolution reaction (HER). However, the large-scale application of MoS₂ is still difficult due to the inherent poor conductivity and insufficient active edge sites. Herein, we develop a simple method to grow P-doped MoS₂ nanosheets on carbon cloth for high efficiency HER. The 2D carbon cloth can prevent the stacking of MoS₂ nanosheets and improve the conductivity with the doping of P atoms. As a result, the P–MoS₂/CC-300 shows the excellent electrocatalytic activity with an overpotential of 81 mV at 10 mA cm^?2 and the lower Tafel slope of 98 mV/dec. Furthermore, it also shows the good electrocatalytic durability for 15 h. This work provides an opportunity for the design of excellent and robust MoS₂-based catalyst via structural engineering and doping method.     

Transition metal carbides coupled with nitrogen-doped carbon as efficient and stable Bi-functional catalysts for oxygen reduction reaction and hydrogen evolution reaction

Developing non-precious metal catalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for proton exchange membrane fuel cell (PEMFC), metal-air batteries and water splitting. Here, we report a in-situ simple approach to synthesize ultra-small sized transition metal carbides (TMCs) nanoparticles coupled with nitrogen-doped carbon hybrids (TMCs/NC, including WC/NC, V₈C₇/NC and Mo₂C/NC). The TMCs/NC exhibit excellent ORR and HER performances in acidic electrolyte as bi-functional catalysts. The potential of WC/NC at the current density of 3.0 mA cm^?2 for ORR is 0.814 V (vs. reversible hydrogen electrode (RHE)), which is very close to Pt/C (0.827 V), making it one of the best TMCs based ORR catalysts in acidic electrolyte. Besides, the TMCs/NC exhibit excellent performances toward HER, the Mo₂C/NC only need an overpotential of 80 mV to drive the current density of 10 mA cm^?2, which is very close to Pt/C (37 mV), making it the competitive alternative candidate among the reported non-precious metal HER catalysts.