Ruthenium Nanoparticles for Catalytic Water Splitting

Interfacial Design of Ti3C2Tx MXene/Graphene Heterostructures Boosted Ru Nanoclusters with High Activity Toward Hydrogen Evolution Reaction

The development of a cost-competitive and efficient electrocatalyst is both attractive and challenging for hydrogen production by hydrogen evolution reaction (HER). Herein, a facile glycol reduction method to construct Ru nanoclusters coupled with hierarchical exfoliated-MXene/reduced graphene oxide architectures (Ru-E-MXene/rGA) is reported. The hierarchical structure, formed by the self-assembly of graphene oxides, can effectively prohibit the self-stacking of MXene nanosheets. Meanwhile, the formation of the MXene/rGA interface can strongly trap the Ru3+ ions, resulting in the uniform distribution of Ru nanoclusters within Ru-E-MXene/rGA. The boosted catalytic activity and underlying catalytic mechanism during the HER process are proved by density functional theory. Ru-E-MXene/rGA exhibits overpotentials of 42 and 62 mV at 10 mA cm-2 in alkaline and acidic electrolytes, respectively. The small Tafel slope and charge transfer resistance (Rct) values elucidate its fast dynamic behavior. The cyclic voltammetry (CV) curves and chronoamperometry test confirm the high stability of Ru-E-MXene/rGA. These results demonstrate that coupling Ru nanoclusters with the MXene/rGA heterostructure represents an efficient strategy for constructing MXene-based catalysts with enhanced HER activity.

High Catalytic Activity of Co-centered 2D Metal Organic Frameworks toward Bifunctional Oxygen Evolution and Reduction Reactions: Rationalized by Spin Polarization Effect

CoX4 (X = NH, S, and O) motifs have demonstrated their high catalytic activity in the platforms of metal organic frameworks (MOFs), however, the underlying reason is still unrevealed. Herein, we propose monolayers constructed by linking TMNxO4-x motifs (TM = Fe, Co, Ni, Cu) with trioxotriangulenes (TOTs) as suitable models to clarify the structure-property-performance relationship of 2D MOFs for the oxygen evolution/reduction reaction (OER/ORR). The highly robust catalytic activity of CoNxO4-x for both the OER and the ORR has been confirmed, even surpassing that of most previously reported 2D MOFs and SACs. This activity is attributed to the moderate interaction between Co and the key intermediate species, which can be modulated by the coordinating atoms. We reveal spin momentum as a reliable activity descriptor in rationalizing the OER/ORR activity, which can be extended to many other 2D MOFs. The elucidated structure-activity relationship is significant for the development of effective bifunctional OER/ORR electrocatalysts.

Orange-peel derived carbon-loaded low content ruthenium nanoparticles as ultra-high performance alkaline water HER electrocatalysts

Carbon materials have a very wide range of applications in the field of electrocatalysis, both as catalyst bodies and as excellent supports for catalysts. In this work, we obtained a graphitic-like orange-peel derived carbon (OPC) material through pre-carbonization and KOH activation strategies using discarded orange-peel as a raw material. OPC has good graphitization characteristics and a few-layer structure, making it very suitable as a support for nanoparticle catalysts. In order to compare the performance of OPC, we used commercial graphene as the benchmark, made two carbon materials uniformly loaded with ruthenium nanoparticles under the same conditions, and obtained two HER catalysts (Ru/OPC and Ru/rGO). The results indicate that Ru/OPC has excellent HER catalytic performance under alkaline conditions, not only superior to Ru/rGO, but also surpassing commercial Pt/C. In 1 M KOH; the overpotential of Ru/OPC is only 3 mV at -10 mA cm-2, greatly exceeding those of Ru/rGO (100 mV) and Pt/C (31 mV). Under high current density (j), the performance of Ru/OPC is even better; the overpotential is 79 mV and 136 mV at -100 mA cm-2 and -200 mA cm-2, respectively. More importantly, Ru/OPC also has a very high TOF and long-term stability, with a TOF of up to 10.62 H2 s-1 at an overpotential of 100 mV and almost no attenuation after 72 h of operation at -50 mA cm-2. Ru/OPC also exhibits good catalytic performance under acidic conditions, significantly superior to that of Ru/rGO. For Ru/OPC, the overpotential is 86 mV, 167 mV and 214 mV at -10 mA cm-2, -100 mA cm-2 and -200 mA cm-2, respectively. Under the same conditions, the overpotential of Ru/rGO is 143 mV, 253 mV and 306 mV at -10 mA cm-2, -100 mA cm-2 and -200 mA cm-2, respectively.

An Unusual Microdomain Factor Controls Interaction of Organic Halides with the Palladium Phase and Influences Catalytic Activity in the Mizoroki-Heck Reaction

In this work, using a combination of scanning and transmission electron microscopy (SEM and TEM), the transformations of palladium-containing species in imidazolium ionic liquids in reaction mixtures of the Mizoroki-Heck reaction and in related organic media are studied to understand a challenging question of the relative reactivity of organic halides as key substrates in modern catalytic technologies. The microscopy technique detects the formation of a stable nanosized palladium phase under the action of an aryl (Ar) halide capable of forming microcompartments in an ionic liquid. For the first time, the correlation between the reactivity of the aryl halide and the microdomain structure is observed: Ar-I (well-developed microdomains) > Ar-Br (microphase present) > Ar-Cl (minor amount of microphase). Previously, it is assumed that molecular level factors, namely, carbon-halogen bond strength and the ease of bond breakage, are the sole factors determining the reactivity of aryl halides in catalytic transformations. The present work reports a new factor connected with the nature of the organic substrates used and their ability to form a microdomain structure and concentrate metallic species, highlighting the importance of considering both the molecular and microscale properties of the reaction mixtures.

Recent advances on surface mounted metal-organic frameworks for energy storage and conversion applications: Trends, challenges, and opportunities

Establishing green and reliable energy resources is very important to counteract the carbon footprints and negative impact of non-renewable energy resources. Metal-organic frameworks (MOFs) are a class of porous material finding numerous applications due to their exceptional qualities, such as high surface area, low density, superior structural flexibility, and stability. Recently, increased attention has been paid to surface mounted MOFs (SURMOFs), which is nothing but thin film of MOF, as a new category in nanotechnology having unique properties compared to bulk MOFs. With the advancement of material growth and synthesis technologies, the fine tunability of film thickness, consistency, size, and geometry with a wide range of MOF complexes is possible. In this review, we recapitulate various synthesis approaches of SURMOFs including epitaxial synthesis approach, direct solvothermal method, Langmuir-Blodgett LBL deposition, Inkjet printing technique and others and then correlated the synthesis-structure-property relationship in terms of energy storage and conversion applications. Further the critical assessment and current problems of SURMOFs have been briefly discussed to explore the future opportunities in SURMOFs for energy storage and conversion applications.

RuO2 Nanostructure as an Efficient and Versatile Catalyst for H2 Photosynthesis

Photocatalytic H₂ generation holds promise in the green production of alternative fuels and valuable chemicals. Seeking alternative, cost-effective, stable, and possibly reusable catalysts represents a timeless challenge for scientists working in the field. Herein, commercial RuO₂ nanostructures were found to be a robust, versatile, and competitive catalyst in H₂ photoproduction in several conditions. We employed it in a classic three-component system and compared its activities with those of the widely used platinum nanoparticle catalyst. We observed a hydrogen evolution rate of 0.137 mol h^-1 g^-1 and an apparent quantum efficiency (AQE) of 6.8% in water using EDTA as an electron donor. Moreover, the favorable employment of l-cysteine as the electron source opens possibilities precluded to other noble metal catalyst. The versatility of the system has also been demonstrated in organic media with impressive H₂ production in acetonitrile. The robustness has been proved by the recovery of the catalyst by centrifugation and reusage alternatively in different media.

Electrochemical Oxidation Encapsulated Ru Clusters Enable Robust Durability for Efficient Oxygen Evolution

Electrochemical oxidization and thermodynamic instability agglomeration are a primary challenge in triggering metal-support interactions (MSIs) by immobilizing metal atoms on a carrier to achieve efficient oxygen evolution reactions (OER). Herein, Ru clusters anchored to the VS₂ surface and the VS₂ nanosheets embedded vertically in carbon cloth (Ru-VS₂ @CC) are deliberately designed to realize high reactivity and exceptional durability. In situ Raman spectroscopy reveals that the Ru clusters are preferentially electro-oxidized to form RuO₂ chainmail, both affording sufficient catalytic sites and protecting the internal Ru core with VS₂ substrates for consistent MSIs. Theoretical calculations elucidate that electrons across the Ru/VS₂ interface aggregate toward the electro-oxidized Ru clusters, while the electronic coupling of Ru 3p and O 2p orbitals boosts a positive shift in the Fermi energy level of Ru, optimizing the adsorption capacity of the intermediates and diminishing the migration barriers of the rate-determining steps. Therefore, the Ru-VS₂ @CC catalyst demonstrated ultra-low overpotentials of 245 mV at 50 mA cm^-2 , while the zinc-air battery maintained a narrow gap (0.62 V) after 470 h of reversible operation. This work has transformed the corrupt into the miraculous and paved a new way for the development of efficient electrocatalysts.

Green Energy by Hydrogen Production from Water Splitting, Water Oxidation Catalysis and Acceptorless Dehydrogenative Coupling

In this review, we want to explain how the burning of fossil fuels is pushing us towards green energy. Actually, for a long time, we have believed that everything is profitable, that resources are unlimited and there are no consequences. However, the reality is often disappointing. The use of non-renewable resources, the excessive waste production and the abandonment of the task of recycling has created a fragile thread that, once broken, may never restore itself. Metaphors aside, we are talking about our planet, the Earth, and its unique ability to host life, including ourselves. Our world has its balance; when the wind erodes a mountain, a beach appears, or when a fire devastates an area, eventually new life emerges from the ashes. However, humans have been distorting this balance for decades. Our evolving way of living has increased the number of resources that each person consumes, whether food, shelter, or energy; we have overworked everything to exhaustion. Scientists worldwide have already said actively and passively that we are facing one of the biggest problems ever: climate change. This is unsustainable and we must try to revert it, or, if we are too late, slow it down as much as possible. To make this happen, there are many possible methods. In this review, we investigate catalysts for using water as an energy source, or, instead of water, alcohols. On the other hand, the recycling of gases such as CO2 and N2O is also addressed, but we also observe non-catalytic means of generating energy through solar cell production.

Facile synthesis of defect-rich RuCu nanoflowers for efficient hydrogen evolution reaction in alkaline media

Developing high-performance electrocatalysts toward hydrogen evolution reaction (HER) in alkaline media is highly desirable for industrial applications in the field of water splitting but is still challenging. Herein, we successfully synthesized RuCu nanoflowers (NFs) with tunable atomic ratios using a facile wet chemistry method. The Ru₃Cu NFs need only 55 mV to achieve a current density of 10 mA cm^-2, which shows ideal durability with only 4 mV decay after 2000 cycles, largely outperforming the catalytic properties of commercial Pt/C. The Ru₃Cu NFs comprise many nanosheets that can provide more active sites for HER. In addition, the introduction of Cu can modulate the electronic structure of Ru, facilitate water dissociation, and optimize H adsorption/desorption ability. Thus, the flower-like structure together with the proper incorporation of Cu boosts HER performance.

Ruthenium/Ruthenium oxide hybrid nanoparticles anchored on hollow spherical Copper-Cobalt Nitride/Nitrogen doped carbon nanostructures to promote alkaline water splitting: Boosting catalytic performance via synergy between morphology engineering, electron transfer tuning and electronic behavior modulation

Exploring bi-functional electrocatalysts with excellent activity, good durability, and cost-effectiveness for electrochemical hydrogen and oxygen evolution reactions (HER and OER) in the same electrolyte is a critical step towards a sustainable hydrogen economy. Three main features such as high density of active sites, improved charge transfer, and optimized electronic configuration have positive effects on the electrocatalyst activity. In this context, understanding structure-composition-property relationships and catalyst activity is very important and highly desirable. Herein, for the first time, we present the design and fabrication of novel MOF-derived ultra-small Ru/RuO₂ nanoparticles doped in copper/cobalt nitride (CuCoN) encapsulated in nitrogen-doped nanoporous carbon framework (NC) (Ru/RuO₂/CuCoN@NC). For the synthesize of this nanocomposite, firstly bimetallic Cu-Co/MOF hollow nanospheres are prepared via a facile emulsion-based interfacial reaction method and used as the template for Ru ion doping (Ru-doped Cu-Co/MOF). Then, Ru-doped Cu-Co/MOF precursor during the carbonization/nitridation/cooling process converted to the Ru/RuO₂/CuCoN@NC nanocomposite. Benefiting from the desirable compositional and structural advantages of more exposed active sites, optimized electronic structure, and interfacial synergy effect, Ru/RuO₂/CuCoN@NC hollow nanosphere electrocatalyst demonstrates striking catalytic performances under alkaline conditions with a current density of 10 mA cm^-2at low overpotentials of 41 mV for HER and 231 mV for OER, respectively. Moreover, as a bifunctional electrocatalyst for overall water splitting, a two-electrode device needs a voltage of 1.51 V to reach a current density of 10 mA cm^-2. Comprehensive electrochemical studies show that the excellent electrocatalytic performance of the Ru/RuO₂/CuCoN@NC hollow nanosphere could be attributed to the improved physical and chemical properties such as desirable compositional, catalysts uniform dispersion, structural advantages of more exposed active sites, optimized electronic structure, high electrical conductivity, and interfacial synergy effect. This work paves a novel avenue for constructing robust bifunctional electrocatalyst for overall water splitting.

Synergic Reaction Kinetics over Adjacent Ruthenium Sites for Superb Hydrogen Generation in Alkaline Media

Ruthenium (Ru)-based electrocatalysts as platinum (Pt) alternatives in catalyzing hydrogen evolution reaction (HER) are promising. However, achieving efficient reaction processes on Ru catalysts is still a challenge, especially in alkaline media. Here, the well-dispersed Ru nanoparticles with adjacent Ru single atoms on carbon substrate (Ru_1,n -NC) is demonstrated to be a superb electrocatalyst for alkaline HER. The obtained Ru_1,n -NC exhibits ultralow overpotential (14.8 mV) and high turnover frequency (1.25 H₂  s^-1 at -0.025 V vs reversible hydrogen electrode), much better than the commercial 40 wt.% Pt/C. The analyses reveal that Ru nanoparticles and single sites can promote each other to deliver electrons to the carbon substrate. Eventually, the electronic regulations bring accelerated water dissociation and reduced energy barriers of hydroxide/hydrogen desorption on adjacent Ru sites, then an optimized reaction kinetics for Ru_1,n -NC is obtained to achieve superb hydrogen generation in alkaline media. This work provides a new insight into the catalyst design in simultaneous optimizations of the elementary steps to obtain ideal HER performance in alkaline media.

Electrocatalytic CO2 Reduction by Molecular Ruthenium Complexes with Polypyridyl Ligands

Two series of ruthenium complexes with various polypyridyl ligands have been prepared. One series of complexes (5 examples) are featured with tetradentate polypyridyl ligands and two acetonitrile molecules at the axial positions of the coordination sphere; the other series (3 examples) include combinations of a tridentate polypyridyl ligand, one 2,2'-bipyridine (bpy) or two picolines, and one acetonitrile ligand. All these complexes were fully characterized by their NMR spectra as well as X-ray single crystal structures. Their electronic absorption and redox data were measured and reported. Of the 8 complexes, three candidates effectively catalyze electrochemical CO 2 reduction reaction (CO 2 RR) in wet acetonitrile medium, generating CO as the major product. All these three catalytically active complexes contain a 2,2':6',2″:6″,2‴-quaterpyridine (qpy) ligand scaffold. A maximum turnover frequency (TOF max ) of > 1000 s -1 was achieved for the electrocatalytic CO 2 reduction at a modest overpotential. On the basis of electrochemical and spectroelectrochemical evidences, the CO 2 substrate was proposed to bind with the ruthenium center at the two-electron reduced state of the complex and then enter the catalytic cycle.

Highly efficient and stable Ru nanoparticle electrocatalyst for the hydrogen evolution reaction in alkaline conditions

Ru nanoparticles are prepared via solvothermal synthesis with allotropism control. Both fcc and hcp samples are active catalysts for the hydrogen evolution reaction, but the hcp sample is stable during 12 hour operation.

Nitrogen-doped carbon encapsulating RuCo heterostructure for enhanced electrocatalytic overall water splitting

The kinetically sluggish electrochemical water splitting reaction still faces great challenges, and the rational design of excellent electrocatalysts is the key to solving the problem. Herein, an etching and pyrolysis...

Hyperdispersed ruthenium nanoparticles anchored on S/N co-doped carbon nanotubes as an efficient HER electrocatalyst

Hyperdispersed ruthenium nanoparticles anchored on S/N co-doped carbon nanotubes show the same high-performance HER catalytic activity as commercial Pt/C.

Ru nanoparticles supported on alginate-derived graphene as hybrid electrodes for the hydrogen evolution reaction

Ultra-small Ru NPs grown on biomass-derived bare/P-doped graphene supports yield efficient and durable electrocatalytic H2 production from water.

Insights into the light-driven hydrogen evolution reaction of mesoporous graphitic carbon nitride decorated with Pt or Ru nanoparticles

Ru or Pt nanoparticles have been prepared following the organometallic approach and deposited onto the surface of mesoporous graphitic carbon nitride (mpg-CN). Three different Ru-based samples have also been compared to investigate the effect of 4-phenylpyridine as a stabilizing agent. The photocatalytic performance towards the hydrogen evolution reaction (HER) has been tested showing that all hybrid systems clearly outperform the photocatalytic activity of bare mpg-CN. In particular, Pt-decorated mpg-CN yields the largest H₂ production upon visible-light irradiation (870 μmol h^-1 g^-1, TOF = 14.1 h^-1, TON = 339 after 24 h) when compared with the Ru-based samples (137-155 μmol h^-1 g^-1, TOFs between 2.3-2.7 h^-1, TONs between 54-57 after 24 h). Long-term photochemical tests (up to 65 h irradiation) show also an improved stability of the Pt-based samples over the Ru counterpart. Photophysical experiments aimed at rationalizing the photocatalytic performance of the different hybrid systems elucidate that the enhanced activity of the Pt-decorated mpg-CN over the Ru-based analogues arises from improved electron transfer kinetics from mpg-CN to the metal nanoparticles.

Design principles of noble metal-free electrocatalysts for hydrogen production in alkaline media: combining theory and experiment

Water electrolysis is a promising solution to convert renewable energy sources to hydrogen as a high-energy-density energy carrier. Although alkaline conditions extend the scope of electrocatalysts beyond precious metal-based materials to earth-abundant materials, the sluggish kinetics of cathodic and anodic reactions (hydrogen and oxygen evolution reactions, respectively) impede the development of practical electrocatalysts that do not use precious metals. This review discusses the rational design of efficient electrocatalysts by exploiting the understanding of alkaline hydrogen evolution reaction and oxygen evolution reaction mechanisms and of the electron structure-activity relationship, as achieved by combining experimental and computational approaches. The enhancement of water splitting not only deals with intrinsic catalytic activity but also includes the aspect of electrical conductivity and stability. Future perspectives to increase the synergy between theory and experiment are also proposed.

Compensating Electronic Effect Enables Fast Site-to-Site Electron Transfer over Ultrathin RuMn Nanosheet Branches toward Highly Electroactive and Stable Water Splitting

To improve the electroactivity and stability of electrocatalysts, various modulation strategies have been applied in nanocatalysts. Among different methods, heteroatom doping has been considered as an effective method, which modifies the local bonding environments and the electronic structures. Meanwhile, the design of novel two-dimensional (2D) nanostructures also offers new opportunities for achieving efficient electrocatalysts. In this work, Mn-doped ultrathin Ru nanosheet branches (RuMn NSBs), a newly reported 2D nanostructure, is synthesized. With the ultrathin and naturally abundant edges, the RuMn NSBs have exhibited bifunctionalities of hydrogen evolution reaction and oxygen evolution reaction with high electroactivity and durability in different electrolytes. Experimental characterizations have revealed that RuO bonds are shortened due to Mn doping, which is the key factor that leads to improved electrochemical performances. Density functional theory (DFT) calculations have confirmed that the introduction of Mn enables flexible modulations on the valence states of Ru sites. The inversed redox state evolutions of Ru and Mn sites not only improve the electroactivity for the water splitting but also the long-term stability due to the pinning effect of Ru sites. This work has provided important inspirations for the design of future advanced Ru-based electrocatalysts with high performances and durability.

Nanoscaled and Atomic Ruthenium Electrocatalysts Confined Inside Super-Hydrophilic Carbon Nanofibers for Efficient Hydrogen Evolution Reaction

A series of Ru-based catalysts have been developed for the hydrogen evolution reaction (HER) by the facile impregnation of copious and eco-friendly bacterial cellulose (BC) with Ru(bpy)₃ Cl₂ (bpy = 2,2'-bipyridine) followed by pyrolysis. After the oxidation and molecular recomposition processes that occur within the BC precursors during pyrolysis, sub-2 nm Ru nanoparticles (NPs) and atomic Ru species confined within surface-oxidized N-doped carbon nanofibers (CNFs) can be observed in the derived catalysts. The surface oxidation of CNFs leads the derived catalysts with super hydrophilicity and water-absorbing capacity, and also provides dimensional confinement for the nanoscaled and atomic Ru species. With these added structural advantages and the component synergy, the derived catalysts show superior HER activities, for which the overpotentials are as low as 19.6 mV (1 m KOH) and 55.0 mV (0.5 m H₂ SO₄ ) for the most active case at the current density of 10 mA cm^-2 . Moreover, superior HER activity can be also achieved for the catalysts derived with a wide range of Ru loadings. Finally, the influence of Ru NP size on HER activity is investigated by density functional theory simulations. This method provides a reliable protocol for preparing highly active HER catalysts for scale-up applications.

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.

Benchmarking Phases of Ruthenium Dichalcogenides for Electrocatalysis of Hydrogen Evolution: Theoretical and Experimental Insights

The hydrogen evolution reaction (HER) is a significant cathode step in electrochemical devices, especially in water splitting, but developing efficient HER catalysts remains a great challenge. Herein, comprehensive density functional theory calculations are presented to explore the intrinsic HER behaviors of a series of ruthenium dichalcogenide crystals (RuX₂ , X = S, Se, Te). In addition, a simple and easily scaled production strategy is proposed to synthesize RuX₂ nanoparticles uniformly deposited on carbon nanotubes. Consistent with theoretical predictions, the RuX₂ catalysts exhibit impressive HER catalytic behavior. In particular, marcasite-type RuTe₂ (RuTe₂ -M) achieves Pt-like activity (35.7 mV at 10 mA cm^-2 ) in an acidic electrolyte, and pyrite-type RuSe₂ presents outstanding HER performance in an alkaline media (29.5 mV at 10 mA cm^-2 ), even superior to that of commercial Pt/C. More importantly, a RuTe₂ -M-based proton exchange membrane (PEM) electrolyzer and a RuSe₂ -based anion exchange membrane (AEM) electrolyzer are also carefully assembled, and their outstanding single-cell performance points to them being efficient cathode candidates for use in hydrogen production. This work makes a significant contribution to the exploration of a new class of transition metal dichalcogenides with remarkable activity toward water electrolysis.

Electrochemical detection of carbendazim in strawberry based on a ruthenium–graphene quantum dot hybrid with a three-dimensional network structure and Schottky heterojunction

The hybrid of a metal with graphene can improve electrochemical properties, but present hybrids cannot break through the limitations of their inherent properties because metals and graphene are conductors.

Ultralow loading of ruthenium nanoparticles on nitrogen-doped porous carbon enables ultrahigh mass activity for the hydrogen evolution reaction in alkaline media

Carbon-supported ultrafine Ru nanoparticles with 0.44 wt% Ru loading displayed ultrahigh activity towards hydrogen evolution reaction in alkaline media.

Ecofriendly ruthenium-containing nanomaterials: synthesis, characterization, electrochemistry, bioactivity and catalysis

Among transition metals, ruthenium being an in-demand element along with its complexes with multidimensional applications in biology, catalysis (especially photocatalysis), and several other aspects of industrial materials, is lacking regards for the potential aspect of its nanoparticles. In the modern synthetic scenario, green synthesis of novel ruthenium nanoparticles for the development of novel materials with potential applications has become a focus. Ru-containing nanomaterials (Ru-cNMs) combined with metals like platinum and palladium or with non-metals like phosphorus and oxygen have shown applications as an anticancer, antimicrobial, and antioxidant agents along with wide-ranging catalytic applications. Reduction of Ru salts using biomaterials including plants etc. has emerged enabling the synthesis of Ru-cNMs. In this context, authors realize that poor availability of literature in this area of research seems to be one of the major handicaps that perhaps could be limiting its attractiveness to researchers. Therefore, it was thought worthwhile to present a review article to encourage, guide, and facilitate scientific researches in green ruthenium nanochemistry embodying synthesis, characterization and biological as well as catalytic applications.

Organocatalytic vs. Ru-based electrochemical hydrogenation of nitrobenzene in competition with the hydrogen evolution reaction

The electrochemical reduction of organic contaminants allows their removal from water. In this contribution, the electrocatalytic hydrogenation of nitrobenzene is studied using both oxidized carbon fibres and ruthenium nanoparticles supported on unmodified carbon fibres as catalysts. The two systems produce azoxynitrobenzene as the main product, while aniline is only observed in minor quantities. Although PhNO2 hydrogenation is the favoured reaction, the hydrogen evolution reaction (HER) competes in both systems under catalytic conditions. H2 formation occurs in larger amounts when using the Ru nanoparticle based catalyst. While similar reaction outputs were observed for both catalytic systems, DFT calculations revealed some significant differences related to distinct interactions between the catalytic material and the organic substrates or products, which could pave the way for the design of new catalytic materials.

Establishing Stability in Organic Semiconductor Photocathodes for Solar Hydrogen Production

As organic semiconductors attract increasing attention to application in the fields of bioelectronics and artificial photosynthesis, understanding the factors that determine their robust operation in direct contact with aqueous electrolytes becomes a critical task. Herein we uncover critical factors that influence the operational stability of donor:acceptor bulk heterojunction photocathodes for solar hydrogen production and significantly advance their performance under operational conditions. First, using the direct photoelectrochemical reduction of aqueous Eu³⁺ and impedance spectroscopy, we determine that replacing the commonly used fullerene-based electron acceptor with a perylene diimide-based polymer drastically increases operational stability and identify that limiting the photogenerated electron accumulation at the organic/water interface to values of ca. 100 nC cm^-2 is required for stable operation (>12 h). These insights are extended to solar-driven hydrogen production using MoS₃, MoP, or RuO₂ water reduction catalyst overlayers where it is found that the catalyst morphology strongly affects performance due to differences in charge extraction. Optimized performance of bulk heterojunction photocathodes coated with a MoS₃:MoP composite gave 1 Sun photocurrent density up to 8.7 mA cm^-2 at 0 V vs RHE (pH 1). However, increased stability was gained with RuO₂ where initial photocurrent density (>8 mA cm^-2) deceased only 15% or 33% during continuous operation for 8 or 20 h, respectively, thus demonstrating unprecedented robustness without a protection layer. This performance represents a new benchmark for organic semiconductor photocathodes for solar fuel production and advances the understanding of stability criteria for organic semiconductor/water-junction-based devices.

Highly-dispersed ruthenium precursors via a self-assembly-assisted synthesis of uniform ruthenium nanoparticles for superior hydrogen evolution reaction

For the first time, highly-dispersed ruthenium precursors via a hydrogen-bond-driven melamine–cyanuric acid supramolecular complex (denoted CAM) self-assembly-assisted synthesis of uniform ruthenium nanoparticles with superior HER performance under both acidic and alkaline conditions are reported. Electrochemical tests reveal that when the current density is −10 mA cm⁻², the optimal Ru/CNO electrocatalyst could express low overpotentials of −18 mV and −46 mV, low Tafel slopes of 46 mV dec⁻¹ and 100 mV dec⁻¹, in 0.5 M H₂SO₄ and 1.0 M KOH, respectively. The remarkable HER performance could be attributed to uniform ruthenium with the aid of highly dispersed ruthenium precursors (Ru–CAM) and subsequent annealing results in uniform ruthenium nanoparticles.

Highly dispersed ruthenium precursors via a supramolecular self-assembly assisted synthesis of uniform ruthenium nanoparticles with excellent HER performance.

In Situ Growth of Amorphous Fe(OH)3 on Nickel Nitrate Hydroxide Nanoarrays for Enhanced Electrocatalytic Oxygen Evolution

Development of highly efficient electrocatalyst for the oxygen evolution reaction (OER) is urgently demanded by the clean hydrogen energy. Herein, in order to further boost the OER activity of metal nitrate hydroxide materials, amorphous Fe(OH)₃ layer is in situ grown on nickel nitrate hydroxide (NiNH) nanoarrays supported on nickel foam (NF) through an interfacial hydrolysis approach, where the loading amount of the Fe(OH)₃ can be simply manipulated by the hydrolysis time. Taking advantage of the synergy of Fe(OH)₃ and NiNH, the optimized Fe(OH)₃@NiNH/NF sample shows a very promising electrocatalytic OER activity in 1 M KOH solution, requiring a very low overpotential of 212 mV vs. reversible hydrogen electrode (RHE) to deliver a geometrical catalytic current density of 100 mA cm^-2 and a low Tafel slope of 49 mV dec^-1. This work provides a new strategy for boosting the electrocatalytic activity of metal hydroxide nitrates through the interface engineering.

Plasma-Deposited Ru-Based Thin Films for Photoelectrochemical Water Splitting

Plasma-enhanced chemical vapor deposition (PECVD) was used to produce new Ru-based thin catalytic films. The surface molecular structure of the films was examined by X-ray photoelectron spectroscopy (XPS). To determine the electro- and photoelectrochemical properties, the oxygen evolution reaction (OER) process was investigated by linear sweep voltammetry (LSV) at pH = 13.6. It was found that Ru atoms were mainly in the metallic state (Ru0) in the as-deposited films, whereas after the electrochemical stabilization, higher oxidation states, mainly Ru+4 (RuO2), were formed. The stabilized films exhibited high catalytic activity in OER—for the electrochemical process, the onset and η10 overpotentials were approx. 220 and 350 mV, respectively, while for the photoelectrochemical process, the pure photocurrent density of about 160 mA/cm2 mg was achieved at 1.6 V (vs. reversible hydrogen electrode (RHE)). The plasma-deposited RuOX catalyst appears to be an interesting candidate for photoanode material for photoelectrochemical (PEC) water splitting.

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.

The role of catalyst–support interactions in oxygen evolution anodes based on Co(OH)2 nanoparticles and carbon microfibers

A set of OER electrodes based on Co(OH)₂ nanoparticles and carbon microfibers of tailored composition is reported, which allows extracting valuable insights on the influence of the metal-support interface in their electrocatalytic performance.

Seed-assisted synthesis of fcc Ru–Cu bimetallic nanostructures and their catalytic properties for the hydrogen evolution reaction

Adjusting the chemical composition and/or crystal structures is an important approach to tune the activity of catalysts.