Ruthenium@N-doped graphite carbon derived from carbon foam for efficient hydrogen evolution reaction

Synergistic Effect of Boron and Oxygen Coordination on Ruthenium Clusters for Industrial Water Splitting in Alkaline Medium

The alteration in the coordination environment of metal atoms can manipulate their electronic structure and regulate the electrocatalytic hydrogen evolution activity. In this work, synchrotron radiation tests prove that the boron (B) and oxygen (O) elements co-coordinate with ruthenium clusters (RuC) on the surface of B-O modified reduced graphene oxide. The electrochemical tests demonstrate that this unique structure electrocatalyst presents an overpotential of 12 mV in 1 M KOH condition and for over 120 h at the current of -1 A cm-2, indicating potential practical applications. The quasi in-situ X-ray photoelectron spectroscopy and in-situ infrared spectroscopy confirmed that the B-O diatomic coordination can modulate the synergy between the substrate and the RuC catalytic site, enhancing the intrinsic catalytic activity and ion migration efficiency. The first principles calculation further proves that B-O diatomic coordination will reduce the desorption barrier of H* and construct a complete hydrogen migration path. This study discloses the significance of the synergistic effect of two anions to enhance the catalytic activity of the catalyst by altering the coordination environment of ruthenium clusters.

Immobilizing Bimetallic RuCo Nanoalloys on Few-Layered MXene as a Robust Bifunctional Electrocatalyst for Overall Water Splitting

Doping Co atoms into Ru lattices can tune the electronic structure of active sites, and the conductive MXene can adjust the electrical conductivity of catalysts, which are both favorable for improving the electrocatalytic activity of the catalyst for water splitting. Here, ruthenium-cobalt bimetallic nanoalloys coupled with exfoliated Ti3 C2 Tx MXene (RuCo-Ti3 C2 Tx ) have been constructed by ice-templated and thermal activation. Due to the strong interaction between the RuCo nanoalloys and conductive MXene, RuCo-Ti3 C2 Tx not only exhibits an excellent hydrogen evolution reaction (HER) performance with a low overpotential and Tafel slope (60 mV, 34.8 mV dec-1 in 0.5 M H2 SO4 and 52 mV, 38.7 mV dec-1 in 1 M KOH), but also good oxygen evolution reaction (OER) performance in an alkaline electrolyte (266 mV, 111.1 mV dec-1 in 1 M KOH). The assembled RuCo-Ti3 C2 Tx ||RuCo-Ti3 C2 Tx electrolyzer requires a lower potential (1.56 V) than does the Pt/C||RuO2 electrolyzer at 10 mA cm-2 . A boosted catalytic HER activity from immobilizing the RuCo nanoalloys on MXene was unveiled by density functional theory calculations. This study provides a feasible and efficient strategy for developing MXene-based catalysts for overall water splitting.

Surface Tailoring-Modulated Bifunctional Oxygen Electrocatalysis with CoP for Rechargeable Zn-Air Battery and Water Splitting

The transition metal phosphide (TMP)-based functional electrocatalysts are very promising for the development of electrochemical energy conversion and storage devices including rechargeable metal-air batteries and water electrolyzer. Tuning the electrocatalytic activity of TMPs is one of the vital steps to achieve the desired performance of these energy devices. Herein, we demonstrate the modulation of the bifunctional oxygen electrocatalytic activity of nitrogen-doped carbon-encapsulated CoP (CoP@NC) nanostructures by surface tailoring with ultralow amount (0.56 atomic %) of Ru nanoparticles (2.5 nm). The CoP at the core and the Ru nanoparticles on the shell have a facile charge transfer interaction with the encapsulating NC. The strong coupling of Ru with CoP@NC boosts the electrocatalytic performance toward oxygen reduction (ORR), oxygen evolution (OER), and hydrogen evolution (HER) reactions. The surface-tailored catalyst requires only 35 mV to deliver the benchmark current density of 10 mA·cm-2 for HER. A small potential gap of 620 mV between ORR and OER is achieved, making the catalyst highly suitable for the development of rechargeable zinc-air batteries (ZABs). The homemade ZAB delivers a specific capacity of 780 mA·hgZn-1 and peak power density of 175 mW·cm-2 with a very small voltaic efficiency loss (1.1%) after 300 cycles. The two-electrode water splitting cell (CoP@NC-Ru||CoP@NC-Ru) delivers remarkably low cell voltage of 1.47 V at the benchmark current density. Stable current density of 25 mA·cm-2 for 25 h without any significant change is achieved. Theoretical studies support the charge transfer interaction-induced enhanced electrocatalytic activity of the surface-tailored nanostructure.

Electronic Modulation and Mechanistic Study of Ru-Decorated Porous Cu-Rich Cuprous Oxide for Robust Alkaline Hydrogen Oxidation and Evolution Reactions

Rational design of high-efficiency and viable electrocatalysts is essential in overcoming the bottleneck of sluggish alkaline hydrogen oxidation/evolution reaction (HOR/HER) kinetics. In this study, a metal-organic framework-derived strategy for constructing a Pt-free catalyst with Ru clusters anchored on porous Cu-Cu₂ O@C is proposed. The designed Ru/Cu-Cu₂ O@C exhibits superior HOR performance, with a mass activity of 2.7 mA  μ g R u - 1 ${{{\rm \mu }{\rm g}}_{{\rm R}{\rm u}}^{-1}}$ at 50 mV, which is about 24 times higher than that of state-of-the-art Pt/C (0.11 mA  μ g P t - 1 ${{{\rm \mu }{\rm g}}_{{\rm P}{\rm t}}^{-1}}$ ). Significantly, Ru/Cu-Cu₂ O@C also displays impressive HER performance by generating 26 mV at 10 mA cm^-2 , which exceeds the majority of documented Ru-based electrocatalysts. Systematic characterization and density functional theory (DFT) calculations reveal that efficient electron transfer between Ru and Cu species results in an attenuated hydrogen binding energy (HBE) of Ru and an enhanced hydroxy binding energy (OHBE) of Cu₂ O, together with an optimized H₂ O adsorption energy with Cu₂ O as the H₂ O*-capturing site, which jointly facilitates HOR and HER kinetics.

Achieving near-Pt hydrogen production on defect nanocarbon via the synergy between carbon defects and heteroatoms

The effect of the synergy between vacancy defects and a phosphorus dopant on the hydrogen evolution reaction (HER) of nanocarbon was revealed for the first time both experimentally and theoretically, and the as-prepared catalysts show near-Pt HER activities, which are the best among metal-free catalysts.

Highly dispersed ruthenium nanoparticles on nitrogen doped carbon toward efficient hydrogen evolution in both alkaline and acidic electrolytes

Efficient and inexpensive electrocatalysts toward the hydrogen evolution reaction (HER) play an important role in electrochemical water splitting. Herein, we report the synthesis of highly dispersed ruthenium nanoparticles (2.2 ± 0.4 nm) on nitrogen doped carbon (Ru/N-C) by chemical reduction of RuCl₃ on carbon in the presence of polyvinylpyrrolidone in combination with subsequent pyrolysis. Ru/N-C exhibits an excellent overpotential of 13.5 and 18.5 mV at 10 mA cm⁻² in 1.0 M KOH and 0.5 M H₂SO₄ aqueous solution, respectively, much better than and comparable to those of commercial Pt/C (38.0 and 10.0 mV). The exceptional HER activity arises from high surface area of ultrafine Ru nanoparticles and appropriate Ru electronic state tuned by nitrogen dopant. Furthermore, Ru/N-C demonstrates excellent durability in both alkaline and acidic condition relative to commercial Pt/C. We speculate that the nitrogen dopant might have coordinated with Ru and tightly anchored Ru nanoparticles, preventing them from agglomerating.

Ultrafine ruthenium nanoparticles on nitrogen doped carbon show exceptional activity toward the hydrogen evolution reaction in alkaline and acidic electrolytes.

Synergetic Function of the Single-Atom Ru-N4 Site and Ru Nanoparticles for Hydrogen Production in a Wide pH Range and Seawater Electrolysis

Hydrogen production by water splitting and seawater electrolysis is a promising alternative to develop clean hydrogen energy. The construction of high-efficiency and durable electrocatalysts for the hydrogen evolution reaction (HER) in a wide pH range and seawater is critical to overcoming the sluggish kinetic process. Herein, we develop an efficient catalytic material composed of a single-atom Ru-N₄ site and Ru nanoparticles anchored on nitrogen-doped carbon (Ru_1+NPs/N-C) through the coordination-pyrolysis strategy of the melamine formaldehyde resin. The Ru_1+NPs/N-C catalyst shows outstanding HER activity with the smallest overpotentials, the lowest Tafel slopes, the highest mass activity and turnover frequency, as well as excellent stability in both acidic and alkaline media. Moreover, Ru_1+NPs/N-C shows comparable hydrogen production performance and a higher faradic efficiency to 20% Pt/C in natural seawater and artificial simulated seawater. Theoretical calculations demonstrate that the strong synergistic effects between the Ru-N₄ site and Ru nanoparticles modify the electronic structure to accelerate the HER kinetics. Ru nanoparticles can effectively realize dissociation of H₂O to generate adsorbed hydrogen and also promote the single-atom Ru-N₄ site to combine adsorbed hydrogen to H₂ and desorption. This work provides a new perspective for designing high-efficiency hydrogen production electrocatalysts for large-scale seawater electrolysis.

The volcanic relationship between HER activity and lattice constant of RuCo alloy nanofilm as a high efficient electrocatalyst

RuCo-ANFs with different proportions can be successfully prepared by magnetron sputtering, and their lattice constants can be adjusted accurately. In the RuCo-ANF, there is an obvious electronic interaction between Ru...

Ru@N/S/TiO2/rGO: a high performance HER electrocatalyst prepared by dye-sensitization

Hydrogen production from water-splitting is one of the most promising hydrogen production methods, and the preparation of the hydrogen evolution reaction (HER) catalyst is very important. Although Pt-based materials have the best catalytic activity for HER, their high price and scarcity greatly limit their large-scale industrial application prospects. Herein, a new method to prepare HER catalyst is described, where dyes used in dye-sensitized solar cells (DSSCs) were used as precursors. A high performance HER catalyst (Ru@N/S/TiO₂/rGO, Ru nanoparticles (NPs) supported on N/S-doped TiO₂/rGO hybrids) was prepared, and the stereoscopic molecular structure of the porphyrin dye, JR1, not only provides a prerequisite for the preparation of the hyperdispersed Ru NPs, but also successfully realizes N/S co-doping. The Ru@N/S/TiO₂/rGO shows an excellent catalytic performance for the HER, which is almost the same as that with Pt/C. In 0.5 M H₂SO₄, the overpotential is 60 mV at 10 mA cm^-2, and the Tafel slope is only 51 mV dec^-1. In 1 M KOH, the overpotential is only 5 mV at 10 mA cm^-2, and the Tafel slope is only 45 mV dec^-1, and this performance is much better than most of the HER catalysts that have been reported. When Ru@N/S/TiO₂/rGO is utilized as a catalyst in an alkaline water electrolyzer, a bias of only 1.52 V is able to complement overall water-splitting at 10 mA cm^-2 (1.78 V, 100 mA cm^-2). The molecular structure and coordination metal species of the dyes are easy to adjust, and the the stereoscopic structure is very helpful for inhibiting the aggregation of the metal NPs, and the strong anchoring effect with TiO₂ or other carbon materials is also very helpful to achieve heteroatom doping. In addition, the process of dye-sensitization is simple and repeatable, and is a novel and efficient method to prepare the electrocatalyst.

Strong Electron Coupling of Ru and Vacancy-Rich Carbon Dots for Synergistically Enhanced Hydrogen Evolution Reaction

The exploitation of ingenious strategies to improve the activity and stability of ruthenium (Ru) is crucial for the advancement of Ru-based electrocatalysts. Vacancy engineering is a typical strategy for modulating the catalytic activity of electrocatalysts. However, creating vacancies directly into pure metallic Ru is difficult because of the extremely stringent conditions required and will result in instability because the integrity of the crystal structure is destroyed. In response, a compromise tactic by introducing vacancies in a Ru composite structure is proposed, and vacancy-rich carbon dots coupled with Ru (Ru@CDs) are elaborately constructed. Specifically, the vacancy-rich carbon dots (CDs) serve as an excellent platform for anchoring and trapping Ru nanoparticles, thus restraining their agglomeration and growth. As expected, Ru@CDs exhibited excellent catalytic performance with a low overpotential of 30 mV at 10 mA cm^-2 in 1 m KOH, a small Tafel slope of 22 mV decade^-1 , and robust stability even after 10 000 cycles. The low overpotential is comparable to those of most previously reported Ru-based electrocatalysts. Additionally, spectroscopic characterizations and theoretical calculations demonstrate that the rich vacancies and the electron interactions between Ru and CDs synergistically lower the intermediate energy barrier and thereby maximize the activity of the Ru@CDs electrocatalyst.

Hierarchical Architectures Based on Ru Nanoparticles/Oxygen-Rich-Carbon Nanotubes for Efficient Hydrogen Evolution

Highly active and durable electrocatalysts are essential for producing hydrogen fuel through the hydrogen evolution reaction (HER). Here, a uniform deposition of Ru nanoparticles strongly interacting with oxygen-rich carbon nanotube architectures (Ru-OCNT) through ozonation and hydrothermal approaches has been designed. The hierarchical structure of Ru-OCNT is made by self-assembly of oxygen functionalities of OCNT. Ru nanoparticles interact strongly with OCNT at the Ru/OCNT interface to give excellent catalytic activity and stability of the Ru-OCNT, as further confirmed by density functional theory. Owing to the hierarchical structure and adjusted surface chemistry, Ru-OCNT has an overpotential of 34 mV at 10 mA cm^-2 with a Tafel slope of 27.8 mV dec^-1 in 1 M KOH, and an overpotential of 55 mV with Tafel slope of 33 mV dec^-1 in 0.5 M H₂ SO₄ . The smaller Tafel slope of Ru-OCNT than Ru-CNT and commercial Pt/C in both alkaline and acidic electrolytes indicates high catalytic activity and fast charge transfer kinetics. The as-proposed chemistry provides the rational design of hierarchically structured CNT/nanoparticle electrocatalysts for HER to produce hydrogen fuel.

Engineering Ruthenium-Based Electrocatalysts for Effective Hydrogen Evolution Reaction

The investigation of highly effective, durable, and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is a prerequisite for the upcoming hydrogen energy society. To establish a new hydrogen energy system and gradually replace the traditional fossil-based energy, electrochemical water-splitting is considered the most promising, environmentally friendly, and efficient way to produce pure hydrogen. Compared with the commonly used platinum (Pt)-based catalysts, ruthenium (Ru) is expected to be a good alternative because of its similar hydrogen bonding energy, lower water decomposition barrier, and considerably lower price. Analyzing and revealing the HER mechanisms, as well as identifying a rational design of Ru-based HER catalysts with desirable activity and stability is indispensable. In this review, the research progress on HER electrocatalysts and the relevant describing parameters for HER performance are briefly introduced. Moreover, four major strategies to improve the performance of Ru-based electrocatalysts, including electronic effect modulation, support engineering, structure design, and maximum utilization (single atom) are discussed. Finally, the challenges, solutions and prospects are highlighted to prompt the practical applications of Ru-based electrocatalysts for HER.

Cobalt disulfide supported on porous carbon foam as a high performance hydrogen evolution reaction catalyst

An excellent cobalt disulfide–carbon foam composite catalyst was synthesized by a hydrothermal method for the electrochemical hydrogen evolution reaction (HER).

Ultrasmall Ru Nanoparticles Highly Dispersed on Sulfur-Doped Graphene for HER with High Electrocatalytic Performance

Nanostructuring and metal-support interactions have been explored as effective methods to improve the electrocatalytic activity in heterogeneous catalysis. In this study, we have fabricated ultrasmall Ru nanoparticles (NPs) dispersed on S-doped graphene (denoted as Ru/S-rGO) by a facile "one-pot" procedure. The experimental results indicated that both the S doping and moderate degree of oxidization of GO can induce the formation and high dispersion of the ultrasmall Ru NPs with larger electrochemically active surface areas for exposing more active sites. Metal-support interaction between S-doped graphene and Ru NPs was observed from the X-ray photoelectron spectroscopy and electronic charge-difference studies. It resulted in the decrease in the electron density of Ru, which facilitated electron release from H₂O and H-OH bond breakage. The results of density functional theory calculation confirmed that the S-dopants could reduce the energy barrier for breaking the H-OH bond to accelerate water dissociation during the alkaline hydrogen evolution reaction (HER). At a current density 20 mA cm^-2, the lowest overpotential of 14 mV, superior to that of Pt/C in alkaline solution, was observed for Ru/S-rGO-24. The observed lowest value of overpotential was because of the ultrasmall size, high dispersion, and metal-support interaction. This work provides a simple and effective method in designing advanced electrocatalysts for the HER in an alkaline electrolyte.

Surface/interface engineering N-doped carbon/NiS2 nanosheets for efficient electrocatalytic H2O splitting

A facile and effective method for preparing bifunctional electrocatalysts with enhanced activity and stability is desired for hydrogen and oxygen production. In this paper, ion-liquid-like (ILL) nickel-urea (Ni-U) was designed and applied to prepare 2D N-doped carbon/NiS₂ (N-C/NiS₂) nanohybrids by a one-step in situ pyrolysis synthesis strategy. The fluidity of ILL Ni-U benefits the interface coupling of the 2D N-C/NiS₂ nanohybrid. Due to the synergistic effect between NiS₂ and N-carbon with high conductivity, the H₂O splitting performance of 2D N-C/NiS₂ nanohybrids was significantly enhanced in alkaline media. The corresponding two-electrode cell only needed 1.53 V to undertake 10 mA cm^-2 for H₂O splitting. Moreover, the resultant 2D N-C/NiS₂ nanohybrids exhibited lasting electrochemical endurance with the maintenance of its stability for more than 48 h. The synthetic strategy not only provides a simple and scalable route for constructing 2D hybrid electrocatalysts, but also paves a way to improve the HER/OER activity of sulphides via the surface/interface engineering strategy.

pH universal Ru@N-doped carbon catalyst for efficient and fast hydrogen evolution

An efficient and robust hydrogen evolution electrocatalyst of Ru nanoparticles embedded in N-doped carbon was obtained by using Bu₄N[Ru(N)Cl₄] and Na₄EDTA as precursors. It exhibits excellent catalytic activity in alkaline solutions and good performance in acidic media.

Nanocomposites Based on Ruthenium Nanoparticles Supported on Cobalt and Nitrogen-Codoped Graphene Nanosheets as Bifunctional Catalysts for Electrochemical Water Splitting

Rational design and engineering of high-efficiency electrocatalysts toward overall water splitting is crucial for the development of hydrogen energy technology. Herein, a facile procedure is described for the preparation of effective bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), where ruthenium nanoparticles are supported on graphene nanosheets that are codoped with atomic cobalt and nitrogen by controlled pyrolysis of melamine-functionalized graphene oxide and metal ion precursors. The obtained nanocomposites (CoNG/Ru) exhibit a remarkable electrocatalytic activity toward both HER and OER in alkaline media, with a respective overpotential of only -15 and +350 mV to reach the current density of 10 mA cm^-2, which is much better than the monometallic counterparts and relevant catalysts in the literature. With CoNG/Ru as bifunctional catalysts for overall water splitting in a two-electrode system, a low potential of 1.58 V is needed to reach the current density of 10 mA cm^-2, which is even better than that with commercial Pt/C and RuO₂ catalysts. This is ascribed to the synergistic interactions between the metal species by metal-metal charge transfer. These results highlight the significance of exploiting the electronic interactions between metal species in carbon-based nanocomposites to develop bifunctional catalysts for electrochemical energy technologies.

Ruthenium Nanoparticles for Catalytic Water Splitting

Both global warming and limited fossil resources make the transition from fossil to solar fuels an urgent matter. In this regard, the splitting of water activated by sunlight is a sustainable and carbon-free new energy conversion scheme able to produce efficient technological devices. The availability of appropriate catalysts is essential for the proper kinetics of the two key processes involved, namely, the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). During the last decade, ruthenium nanoparticle derivatives have emerged as true potential substitutes for the state-of-the-art platinum and iridium oxide species for the HER and OER, respectively. Thus, after a summary of the most common methods for catalyst benchmarking, this review covers the most significant developments of ruthenium-based nanoparticles used as catalysts for the water-splitting process. Furthermore, the key factors that govern the catalytic performance of these nanocatalysts are discussed in view of future research directions.

High-Performance Ru@C4N Electrocatalyst for Hydrogen Evolution Reaction in Both Acidic and Alkaline Solutions

We report a high-performance Ru@C₄N electrocatalyst for the hydrogen evolution reaction (HER) in both acidic and alkaline solutions. This catalyst is synthesized by annealing a complex of a covalent organic framework compound coordinated with ruthenium synthesized by a "one-pot" solvothermal method. This Ru@C₄N catalyst shows excellent electrocatalytic activity toward the hydrogen evolution reaction (HER) in both acidic and alkaline solutions with very low overpotentials at 10 mA/cm² (6 mV in 0.5 M H₂SO₄ solution; 7 mV in 1.0 M KOH solution), which outperforms the commercial catalyst Pt/C. The Ru@C₄N electrocatalyst also exhibits high HER turnover frequencies of 0.93 H₂ per s in 0.5 M H₂SO₄ and 0.65 H₂ per s in 1.0 M KOH solutions at 25 mV as well as superior performance stability.

Tunable doping of N and S in carbon nanotubes by retarding pyrolysis-gas diffusion to promote electrocatalytic hydrogen evolution

The doping amount of heteroatoms in N, S co-doped carbon nanotubes (CNT-NS) was accurately and extensively regulated by retarding pyrolysis-gas diffusion. The effect of the content of N and S on the hydrogen evolution activity of CNT-NS was revealed for the first time both experimentally and theoretically.