Noble Metal Phosphides: Robust Electrocatalysts toward Hydrogen Evolution Reaction

Facing with serious carbon emission issues, the production of green H2 from electrocatalytic hydrogen evolution reaction (HER) has received extensive research interest. Almost all kinds of noble metal phosphides (NMPs) consisting of Pt-group elements (i.e., Ru, Rh, Pd, Os, Ir and Pt) are all highly active and pH-universal electrocatalysts toward HER. In this review, the recent progress of NMP-based HER electrocatalysts is summarized. It is further take typical examples for discussing important impact factors on the HER performance of NMPs, including crystalline phase, morphology, noble metal element and doping. Moreover, the synthesis and HER application of hybrid catalysts consisting of NMPs and other materials such as transition metal phosphides, oxides, sulfides and phosphates, carbon materials and noble metals is also reviewed. Reducing the use of noble metal is the key idea for NMP-based hybrid electrocatalysts, while the expanded functionality and structure-performance relationship are also noticed in this part. At last, the potential opportunities and challenges for this kind of highly active catalyst is discussed.

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.

Hydroxyapatite-Derived Heterogeneous Ru-Ru2 P Electrocatalyst and Environmentally-Friendly Membrane Electrode toward Efficient Alkaline Electrolyzer

Alkaline membrane water electrolysis is a promising production technology, and advanced electrocatalyst and membrane electrode design have always been the core technology. Herein, an ion-exchange method and an environmentally friendly in situ green phosphating strategy are successively employed to fabricate Ru-Ru₂ P heterogeneous nanoparticles by using hydroxyapatite (HAP) as a phosphorus source, which is an exceptionally active electrocatalyst for hydrogen evolution reaction (HER). Density functional theory calculation results reveal that strong electronic redistribution occurs at the heterointerface of Ru-Ru₂ P, which modulates the electronic structure to achieve an optimized hydrogen adsorption strength. The obtained Ru-Ru₂ P possesses excellent HER performance (24 mV at 10 mA cm^-2 ) and robust stability (1000 mA cm^-2 for 120 h) in alkaline media. Furthermore, an environmentally friendly membrane electrode with a sandwich structure is assembled by HAP nanowires as an alkaline membrane, Ru-Ru₂ P as a cathodic catalyst, and NiFe-LDH as an anodic catalyst, respectively. The voltage of (-) Ru-Ru₂ P || NiFe-LDH/CNTs (+) (1.53 V at 10 mA cm^-2 ) is lower than that of (-) 20 wt% Pt/C || RuO₂ (+) (1.60 V at 10 mA cm^-2 ) for overall water splitting. Overall, the studies not only design an efficient catalyst but also provide a new route to achieve a high-stability electrolyzer for industrial H₂ production.

Phosphorus-Rich Ruthenium Phosphide Embedded on a 3D Porous Dual-Doped Graphitic Carbon for Hydrogen Evolution Reaction

Metal phosphides have recently emerged as promising electrocatalysts for hydrogen evolution reaction (HER). Herein, we report the synthesis of ruthenium diphosphide embedded on a dual-doped graphitic carbon by pyrolyzing chitosan beads impregnated with ruthenium chloride and phosphorus pentoxide. The as-synthesized RuP₂@N-P-C displays a good electrocatalytic activity in acidic, neutral and alkaline media. We show that the HER activity of the electrocatalyst can be tuned by varying the concentration of Li⁺ cations. Co-diffusion effects on H⁺ exerted by Li⁺ on HER in the porous carbon matrix have been observed.

Superionic conductor Ag2Se modulated CoSe2 nanosheets prepared via monometallic cation release for efficient pH-universal water electrolysis into hydrogen

Superionic conductors regulated transition metal chalcogenides are the newly emerged electrocatalyst in water electrolysis into clean hydrogen and oxygen. However, there is still much room for the development of structural design, electronic modulation and heterogeneous interface construction to improve the overall water splitting performance in pH-universal solutions, especially in alkaline and neutral mediums. Herein, using β-cyclodextrin (β-CD) and citric acid (CA) organics with abundant hydroxyl (-OH) and carboxyl (-COOH), a special Ag₂Se nanoparticles-decorated CoSe₂ flower-like nanosheets loaded on porous and conductive nickel foam substrate (Ag₂Se-CoSe₂/NF) was successfully constructed by a new method of monometallic cation release of coordinated cobalt. The Ag₂Se phase exerts the nature characteristics of superionic conductors to modulate the morphological and electronic structures of CoSe₂ as well as improve its conductivity. The generated rich active interfaces and abundant Se vacancy defects facilitate numerous active sites exposure to accelerate the hydrogen ion transport and charge transfer. Compared to the single-phase Ag₂Se/NF-8 and CoSe₂/NF, the prepared Ag₂Se-CoSe₂/NF-8 with a two-phase synergistic effect achieves an outstanding pH-universal electrocatalytic hydrogen production performance by water electrolysis, as evidenced by a lower overpotential (60 mV, 212 mV and 85 mV vs RHE at 10 mA cm^-2 for pH = 0.36, 7.00 and 13.70, respectively). Only a voltage of 1.55 V at 10 mA cm^-2 is required to implement the overall water splitting in an alkaline electrolyzer. This work provides significant guidance for the future designation and practical development of transition metal chalcogenides with superionic conductors applied in the electrocatalytic field.

Ordered micropattern arrays fabricated by lung-derived dECM hydrogels for chemotherapeutic drug screening

AIMS

This study aims to evaluate ECM-coated micropattern arrays derived from decellularization of native porcine lungs as a novel three-dimensional cell culture platform.

METHODS

ECM derived from decellularization of native porcine lungs was exploited to prepare hydrogels. Then, dECM-coated micropattern arrays were fabricated at four different diameters (50, 100, 150 and 200 ​μm) using polydimethylsiloxane (PDMS). Two lung cancer cell lines, A549 and H1299, were tested on a dECM-coated micropattern array as a novel culture platform for cell adhesion, distribution, proliferation, viability, phenotype expression, and drug screening to evaluate the cytotoxicity of paclitaxel, doxorubicin and cisplatin.

RESULTS

The ECM derived from decellularization of native porcine lungs supported cell adhesion, distribution, viability and proliferation better than collagen I and Matrigel as the coated matrix on the surface. Moreover, the optimal diameter of the micropattern arrays was 100-150 ​μm, as determined by measuring the morphology, viability, proliferation and phenotype of the cancer cell spheroids. Cell spheroids of A549 and H1299 on dECM-coated micropattern arrays showed chemoresistance to anticancer drugs compared to that of the monolayer. The different distributions of HIF-1α, MCL-1 (in the center) and Ki-67 and MRP2 (in the periphery) of the spheroids demonstrated the good establishment of basal-lateral polarity and explained the chemoresistance phenomenon of spheroids.

CONCLUSIONS

This novel three-dimensional cell culture platform is stable and reliable for anticancer drug testing. Drug screening in dECM-coated micropattern arrays provides a powerful alternative to existing methods for drug testing and metabolic profiling in the drug discovery process.

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.

Reversing the Nucleophilicity of Active Sites in CoP2 Enables Exceptional Hydrogen Evolution Catalysis

Precisely constructing the local configurations of active sites to achieve on-demand catalytic functions is highly critical yet challenging. Herein, an anion-deficient strategy to precisely capture Ru single atoms on the anion vacancies of CoP₂ (Ru-SA/Pv-CoP₂ ) is developed. Refined structural characterizations reveal that the Ru single atoms preferably bind to the anion vacancy sites and consequently build a superior catalytic surface with neighboring CoP and CoRu coordination states for the hydrogen evolution reaction (HER) catalysis. The prepared Ru-SA/Pv-CoP₂ nanowires exhibit an unprecedented overpotential of 17 mV at 10 mA cm^-2_geo , and the corresponding mass activity is 52.2 times higher than the benchmark Pt/C catalyst at the overpotential of 50 mV. Theoretical analysis illustrates that the introduced Ru-SAs can reverse electrons state distribution (from nucleophilic P sites to electrophilic Ru sites) and boost the activation of water molecules and hydrogen production. More importantly, such a construction strategy is also applicable for Pt single atom coupling, suggesting its generality in building catalytic sites. The capability to precisely construct active sites offers a powerful platform to manipulate the catalytic performance of HER catalysts and beyond.

Phosphorus-Alloying as a Powerful Method for Designing Highly Active and Durable Metal Nanoparticle Catalysts for the Deoxygenation of Sulfoxides: Ligand and Ensemble Effects of Phosphorus

The modification of metal nanoparticles (NPs) by incorporating additional metals is a key technique for developing novel catalysts. However, the effects of incorporating nonmetals into metal NPs have not been widely explored, particularly in the field of organic synthesis. In this study, we demonstrate that phosphorus (P)-alloying significantly increases the activity of precious metal NPs for the deoxygenation of sulfoxides into sulfides. In particular, ruthenium phosphide NPs exhibit an excellent catalytic activity and high durability against sulfur-poisoning, outperforming conventional catalysts. Various sulfoxides, including drug intermediates, were deoxygenated to sulfides with excellent yields. Detailed investigations into the structure-activity relationship revealed that P-alloying plays a dual role: it establishes a ligand effect on the electron transfer from Ru to P, facilitating the production of active hydrogen species, and has an ensemble effect on the formation of the Ru-P bond, preventing strong coordination with sulfide products. These effects combine to increase the catalytic performance of ruthenium phosphide NPs. These results demonstrate that P-alloying is an efficient method to improve the metal NP catalysis for diverse organic synthesis.

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...

Highly efficient sub-nanometer RuxCuyP2 nanoclusters designed for hydrogen evolution under alkaline media

Design of highly active and stable non-precious electrocatalysts towards hydrogen evolution reaction (HER) is a hot research topic in low cost, clean and sustainable hydrogen energy field, yet remaining the important challenge caused by the sluggish reaction kinetics for water-alkali electrolyzers. Herein, a robust electrocatalyst is proposed by designing a novel sub-nanometer of copper and ruthenium bimetallic phosphide nanoclusters (Ru_xCu_yP₂) supported on a graphited carbon nanofibers (CNF). Uniform Ru_xCu_yP₂ (~1.90 nm) on the surface of CNF are obtained by introducing the dispersed Ru, thereby improving the intrinsic activity for HER. On optimizing the Ru ratio, the (x = y = 1) RuCuP₂/CNF catalyst exhibits an excellent HER electroactivity with an overpotential of 10 mV in 1.0 M NaOH electrolyte to produce 10 mA cm^-2 current density, which is lower than commercial 20% Pt/C in alkaline solution. Moreover, the kinetic study demonstrated that electrochemical activation energies for HER of RuCuP₂/CNF is 20.7 kJ mol^-1 highest among different ratio bimetallic phosphide. This simple, cost-effective, and environmentally friendly methodology can pave the way for exploitation of bimetallic phosphide nanoclusters for catalyst design.

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.

Natural DNA-assisted RuP2 on highly graphitic N,P-codoped carbon for pH-wide hydrogen evolution

Natural DNA was employed for the first time as a phosphorization agent and carbon source to controllably synthesize a RuP₂/N,P-codoped carbon composite by a simple "mix-and-pyrolyze" strategy, which displays higher activity for alkaline and acidic HER and neutral activity compared to Pt/C together with outstanding durability.

Self-Limiting Growth of Single-Layer N-Doped Graphene Encapsulating Nickel Nanoparticles for Efficient Hydrogen Production

Effective nonprecious metal catalysts are urgently needed for hydrogen evolution reaction (HER). The hybridization of N-doped graphene and a cost-effective metal is expected to be a promising approach for enhanced HER performance but faces bottlenecks in controllable fabrication. Herein, a silica medium-assisted method is developed for the high-efficient synthesis of single-layer N-doped graphene encapsulating nickel nanoparticles (Ni@SNG), where silica nanosheets molecule sieves tactfully assist the self-limiting growth of single-layer graphene over Ni nanoparticles by depressing the diffusion of gaseous carbon radical reactants. The Ni@SNG sample synthesized at 800 °C shows excellent activity for HER in alkaline medium with a low overpotential of 99.8 mV at 10 mA cm^-2, which is close to that of the state-of-the-art Pt/C catalyst. Significantly, the Ni@SNG catalyst is also developed as a binder-free electrode in magnetic field, exhibiting much improved performance than the common Nafion binder-based electrode. Therefore, the magnetism adsorption technique will be a greatly promising approach to overcome the high electron resistance and poor adhesive stability of polymer binder-based electrodes in practical applications.

Ru-Doping Enhanced Electrocatalysis of Metal-Organic Framework Nanosheets toward Overall Water Splitting

An Ru-doping strategy is reported to substantially improve both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalytic activity of Ni/Fe-based metal-organic framework (MOF) for overall water splitting. As-synthesized Ru-doped Ni/Fe MIL-53 MOF nanosheets grown on nickel foam (MIL-53(Ru-NiFe)@NF) afford HER and OER current density of 50 mA cm^-2 at an overpotential of 62 and 210 mV, respectively, in alkaline solution with a nominal Ru loading of ≈110 μg cm^-2 . When using as both anodic and cathodic (pre-)catalyst, MIL-53(Ru-NiFe)@NF enables overall water splitting at a current density of 50 mA cm^-2 for a cell voltage of 1.6 V without iR compensation, which is much superior to state-of-the-art RuO₂ -Pt/C-based electrolyzer. It is discovered that the Ru-doping considerably modulates the growth of MOF to form thin nanosheets, and enhances the intrinsic HER electrocatalytic activity by accelerating the sluggish Volmer step and improving the intermediate oxygen adsorption for increased OER catalytic activity.

Excessive Se on RuSe2 nanocrystals to accelerate water dissociation for the enhanced electrocatalytic hydrogen evolution reaction

Selenium-enriched RuSe2 (RuxSe) nanocrystals as electrocatalysts for the HER in basic media have been synthesized via a facile hydrothermal method followed by a calcination process. The catalytic activity of the obtained RuxSe nanocrystals is greatly dependent on calcination temperatures. The nanocrystals obtained at 400 °C (RuxSe-400) demonstrate the highest HER activity with a low overpotential of 45 mV to deliver a current density of 10 mA cm-2 and a small Tafel slope of 31.4 mV dec-1. The enhanced catalytic HER performance of RuxSe-400 could be attributed to the excessive Se on the RuSe2 nanocrystal surface. Density functional theory (DFT) calculations reveal that the excessive Se would lower the energy barrier for water dissociation and lessen the dependence on the Ru sites for OH* adsorption but have a negligible effect on hydrogen adsorption energy, leading to an accelerated HER process. Furthermore, the excessive Se on the nanocrystal surface further endows the catalyst with promoted charge-transfer kinetics, ensuring a more efficient catalytic reaction. The strategy herein for the design of highly efficient HER catalysts by engineering the separation of different intermediate (H* and OH*) adsorption sites is expected to be extended to other electrocatalysts for high-efficiency energy conversion.

An Efficient RuTe2 /Graphene Catalyst for Electrochemical Hydrogen Evolution Reaction in Acid Electrolyte

Developing efficient powder catalysts for hydrogen evolution reaction (HER) in the acidic electrolyte is significant for hydrogen generation in the proton exchange membrane (PEM) water electrolysis technique. Herein, we demonstrated an efficient catalyst for HER in the acid media based on the graphene supported ruthenium telluride nanoparticles (RuTe₂ /Gr). The catalysts were easily fabricated by a facile microwave irradiation/thermal annealing approach, and orthorhombic RuTe₂ crystals were found anchored over the graphene surface. The defective structure was demonstrated in the aberration-corrected transmission electron microscopy images for RuTe₂ crystals and graphene support. This catalyst required an overpotential of 72 mV to drive 10 mA cm^-2 for HER when loading on the inert glass carbon electrode; Excellent catalytic stability in acidic media was also observed to offer 10 mA cm^-2 for 10 hours. The Volmer-Tafel mechanism was indicated on RuTe₂ /Gr catalyst by Tafel slope of 33 mV dec^-1 , similar to that of Pt/C catalysts. The high catalytic performance of RuTe₂ /Gr could be attributed to its high dispersion on the graphene surface, high electrical conductivity and low charge transfer resistance. This powder catalyst has potential application in the PEM water electrolysis technique because of its low cost and high stability.

Charge Redistribution Caused by S,P Synergistically Active Ru Endows an Ultrahigh Hydrogen Evolution Activity of S-Doped RuP Embedded in N,P,S-Doped Carbon

Water splitting for production of hydrogen as a clean energy alternative to fossil fuel has received much attention, but it is still a tough challenge to synthesize electrocatalysts with controllable bonding and charge distribution. In this work, ultrafine S-doped RuP nanoparticles homogeneously embedded in a N, P, and S-codoped carbon sheet (S-RuP@NPSC) is synthesized by pyrolysis of poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS) as the source of C/N/S/P. The bondings between Ru and N, P, S in PZS are regulated to synthesize RuS2 (800 °C) and S-RuP (900 °C) by different calcination temperatures. The S-RuP@NPSC with low Ru loading of 0.8 wt% with abundant active catalytic sites possesses high utilization of Ru, the mass catalytic activity is 22.88 times than 20 wt% Pt/C with the overpotential of 250 mV. Density functional theory calculation confirms that the surface Ru (-0.18 eV) and P (0.05 eV) are catalytic active sites for the hydrogen evolution reaction (HER), and the according charge redistribution of Ru is regulated by S and P with reverse electronegativity and electron-donor property to induce a synergistically enhanced reactivity toward the HER. This work provides a rational method to regulate the bonding and charge distribution of Ru-based electrocatalysts by reacting macromolecules with multielement of C/N/S/P with Ru.

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.

RuP nanoparticles on ordered macroporous hollow nitrogen-doped carbon spheres for efficient hydrogen evolution reaction

The design of highly active, Earth-abundant and stable electrocatalysts is important for efficient water splitting. In this work, we report the fabrication of RuP and Ru₂P nanoparticles supported on ordered macroporous N-doped carbon hollow spheres (RuP/H-NC and Ru₂P/H-NC) through a facile and scalable space-confined pyrolysis process. The RuP/H-NC catalyst exhibits Pt-like activity in alkaline electrolyte, by means of the macroporous structure with a larger specific area and more exposed active sites, as well as the synergistic effect between the RuP nanoparticles and N-doped carbon. Specifically, the RuP/H-NC catalyst yields superior hydrogen evolution reaction activity in terms of low overpotential of 19 mV in 1 M KOH to achieve a current density of 10 mA cm^-2 and excellent durability, outperforming Ru₂P/H-NC and most of the reported non-Pt catalysts. Further density function theory calculation reveals that RuP is more intrinsically active with favorable hydrogen adsorption Gibbs free energy than that of Ru₂P.

Facile in situ fabrication of biomorphic Co2P-Co3O4/rGO/C as an efficient electrocatalyst for the oxygen reduction reaction

Streptococcus thermophilus, a Gram-positive (G+) bacterium featuring a teichoic acid-rich cell wall, has been employed as both a phosphorus source and template to synthesize a biomorphic Co2P-Co3O4/rGO/C composite as an efficient electrocatalyst for the oxygen reduction reaction (ORR). Different from the conventional method for the synthesis of phosphides, bio-derivative phosphorus vapor was emitted from the inside out, which facilitated the in situ transformation of the chemically adsorbed Co precursor on the bacteria into Co2P-Co3O4 heterogeneous nanoparticles, which featured a Co2P-rich body and Co3O4-rich surface. Besides, reduced graphene oxide (rGO) was also introduced in the synthetic process to keep Co2P-Co3O4 scattered and further promote the electron transport efficiency. All the Co2P-Co3O4 nanoparticles and rGO sheets were supported on the bacteria-derived carbon substrate with submicron-spherical morphology. The as-obtained Co2P-Co3O4/rGO/C composite exhibited excellent electrocatalytic performance for ORR with onset and half-wave potentials of 0.91 and 0.80 V vs. RHE, respectively. Furthermore, its long-term stability and methanol tolerance were better than those of commercial Pt/C. Thus, this work presents a new strategy of using an interior bio-phosphorus source to obtain heterojunction particles featuring a phosphide-rich body and oxide-rich surface, which may provide some insights for the construction of efficient heterogeneous electrocatalysts.

Hollow Nanotube Ru/Cu2+1 O Supported on Copper Foam as a Bifunctional Catalyst for Overall Water Splitting

Hydrogen energy is considered as one of the ideal clean energies for solving the energy shortage and environmental issues, and developing highly efficient electrocatalysts for overall water splitting to produce hydrogen is still a huge challenge. Herein, for the first time, Ru-doped Cu₂₊₁ O vertically arranged nanotube arrays in situ grown on Cu foam (Ru/Cu₂₊₁ O NT/CuF) are reported and further investigated for their catalytic properties for overall water splitting. The Ru/Cu₂₊₁ O NT/CuF presents ultrahigh catalytic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline conditions, and it exhibits a small overpotential of 32 mV at 10 mA cm^-2 in the HER, and only needs 210 mV overpotential to achieve a current density of 10 mA cm^-2 in the OER. Importantly, the alkaline electrolyzer using Ru/Cu₂₊₁ O NT/CuF as a bifunctional electrocatalyst only needs 1.53 V voltage to deliver a current density of 10 mA cm^-2 , which is much lower than the benchmark of IrO₂ (+)/Pt(-) counterpart (1.64 V at 10 mA cm^-2 ). The excellent performance of the Ru/Cu₂₊₁ O NT/CuF catalyst is attributed to its high conductive substrate and special Ru-doped nanotube structure, which provides a high electrochemical active surface area and 3D gas diffusion channel.

A Roadmap to Low-Cost Hydrogen with Hydroxide Exchange Membrane Electrolyzers

Hydrogen is an ideal alternative energy carrier to generate power for all of society's energy demands including grid, industrial, and transportation sectors. Among the hydrogen production methods, water electrolysis is a promising method because of its zero greenhouse gas emission and its compatibility with all types of electricity sources. Alkaline electrolyzers (AELs) and proton exchange membrane electrolyzers (PEMELs) are currently used to produce hydrogen. AELs are commercially mature and are used in a variety of industrial applications, while PEMELs are still being developed and find limited application. In comparison with AELs, PEMELs have more compact structure and can achieve higher current densities. Recently, however, an alternative technology to PEMELs, hydroxide exchange membrane electrolyzers (HEMELs), has gained considerable attention due to the possibility to use platinum group metal (PGM)-free electrocatalysts and cheaper membranes, ionomers, and construction materials and its potential to achieve performance parity with PEMELs. Here, the state-of-the-art AELs and PEMELs along with the current status of HEMELs are discussed in terms of their positive and negative aspects. Additionally discussed are electrocatalyst, membrane, and ionomer development needs for HEMELs and benchmark electrocatalysts in terms of the cost-performance tradeoff.

Low-Cost Porous Ruthenium Layer Deposited on Nickel Foam as a Highly Active Universal-pH Electrocatalyst for the Hydrogen Evolution Reaction

Low-cost and high-efficiency electrocatalysts for the hydrogen evolution reaction (HER) are a key constituent of a low-carbon industrial economy based on intermittent energy production in the near future. A facile wet-chemistry strategy has been developed for the synthesis of a porous Ru layer deposited onto Ni foam (NF) as a competitive candidate for HER over the whole pH range, especially under economical alkaline conditions. The catalyst shows outstanding HER performance, which stems from the porosity of the Ru layer, the electronic structure of the electrode, and the charge transfer between the NF and the Ru layer, which gives rise to the strong activity of the Ru layer in the HER process. Moreover, the Ru loading was as low as approximately 1.1 wt %, representing significant potential for application in cost-effective HER.

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.

Benchmarking Three Ruthenium Phosphide Phases for Electrocatalysis of the Hydrogen Evolution Reaction: Experimental and Theoretical Insights

The outstanding electrocatalytic activity of ruthenium (Ru) phosphides toward the hydrogen evolution reaction (HER) has received wide attention. However, the effect of the Ru phosphide phase on the HER performance remains unclear. Herein, a two-step method was developed to synthesize nanoparticles of three types of Ru phosphides, namely, Ru₂ P, RuP, and RuP₂ , with similar morphology, dimensions, loading density, and electrochemical surface area on graphene nanosheets by simply controlling the dosage of phytic acid as P source. Electrochemical tests revealed that Ru₂ P/graphene shows the highest intrinsic HER activity, followed by RuP/graphene and RuP₂ /graphene. Ru₂ P/graphene affords a current density of 10 mA cm^-2 at an overpotential of 18 mV in acid media. Theoretical calculations further showed that P-deficient Ru₂ P has a lower free energy of hydrogen adsorption on the surface than other two, P-rich Ru phosphides (RuP, RuP₂ ), which confirms the excellent intrinsic HER activity of Ru₂ P and is consistent with experiment results. The work reveals for the first time a clear trend of HER activity among three Ru phosphide phases.

Ru x Se@MoS2 hybrid as a highly efficient electrocatalyst toward hydrogen evolution reaction

Alkaline hydrogen evolution reaction (HER) requires highly efficient and stable catalytic materials, the engineering of which needs overall consideration of the water dissociation process as well as the intermediate hydrogen adsorption process. Herein, a Ru x Se@MoS2 hybrid catalyst was synthesized by the decoration of MoS2 with Ru x Se nanoparticles through a two-step hydrothermal reaction. Due to the bifunctionality mechanism in which Ru promotes the water dissociation and the nearby Se atoms, unsaturated Mo and/or S atoms act as active sites for the intermediate hydrogen adsorption, the hybrid catalyst exhibits an exceptional HER performance in basic media with a rather low overpotential of 45 mV at a current density of 10 mA cm-2 and a small Tafel slope of 42.9 mV dec-1. The synergetic effect between Ru x Se and MoS2 not only enables more catalytically active sites, but also increases the inherent conductivity of the hybrid catalyst, leading to more favorable HER kinetics under both alkaline and acidic conditions. As a result, Ru x Se@MoS2 also demonstrates an enhanced catalytic activity toward HER in 0.5 M H2SO4 in comparison with pure Ru x Se and MoS2, which requires an overpotential of 120 mV to deliver a 10 mA cm-2 current density and gives a Tafel slope of 72.2 mV dec-1. In addition, the hybrid electrocatalyst also exhibits superior electrochemical stability during the long-term HER process in both acidic media and alkaline media.

Ball Milling-Assisted Synthesis of Ultrasmall Ruthenium Phosphide for Efficient Hydrogen Evolution Reaction

The development of scalable hydrogen production technology to produce hydrogen economically and in an environmentally friendly way is particularly important. The hydrogen evolution reaction (HER) is a clean, renewable, and potentially cost-effective pathway to produce hydrogen, but it requires the use of a favorable electrocatalyst which can generate hydrogen with minimal overpotential for practical applications. Up to now, ruthenium phosphide Ru2P has been considered as a high-performance electrocatalyst for the HER. However, a tedious post-treatment method as well as large consumption of solvents in conventional solution-based synthesis still limits the scalable production of Ru2P electrocatalysts in practical applications. In this study, we report a facile and cost-effective strategy to controllably synthesize uniform ultrasmall Ru2P nanoparticles embedded in carbon for highly efficient HER. The key to our success lies in the use of a solid-state ball milling-assisted technique, which overcomes the drawbacks of the complicated post-treatment procedure and large solvent consumption compared with solution-based synthesis. The obtained electrocatalyst exhibits excellent Pt-like HER performance with a small overpotential of 36 mV at current density of 10 mA cm−2 in 1 M KOH, providing new opportunities for the fabrication of highly efficient HER electrocatalysts in real-world applications.

In pursuit of advanced materials from single-source precursors based on metal carbonyls

In this perspective, the development of single-source precursors and their relative advantages over multiple source approaches for the synthesis of metal pnictide solid state materials is explored. Particular efforts in the selective production of iron phosphide materials for catalytic applications are discussed, especially directed towards the hydrogen evolution and oxygen evolution reactions of water splitting.

Transition metal atom (Ti, V, Mn, Fe, and Co) anchored silicene for hydrogen evolution reaction

Non-noble element catalysis for hydrogen evolution reaction (HER) is a promising pathway for mass hydrogen production through electrochemical water splitting. In this work, the catalytic performance of metal (alkali, alkali-earth, and transition metal) atoms anchored to silicene was investigated by density functional theory. Results showed that all the studied metal atoms are energetically favorably absorbed on the silicene with large binding energies. The pristine silicene is catalytically inert for HER, while the metal (Fe, V, Mn, Ti, Co, Ni, Be, and Cr) atom anchored silicene is catalytically active for HER with the calculated Gibbs free energies in the range between −0.09 and 0.18 eV, which is very close to the optimum value of 0.0 eV. These results suggested that the catalytic behavior of silicene can be effectively improved by metal adsorption. Such metal (Fe, V, Mn, Ti, Co, Ni, Be, and Cr) atom anchored silicenes can be used as potential catalysts for HER.

Ti, V, Mn, Fe, and Co anchored silicene as low-cost catalysts for hydrogen evolution reaction.

Controllable fabrication of uniform ruthenium phosphide nanocrystals for the hydrogen evolution reaction

Ruthenium phosphide (Ru₂P and RuP) nanocrystals are controllably fabricated, and exhibit a remarkable hydrogen evolution reaction performance.

Electrochemical hydrogen evolution reaction boosted by constructing Ru nanoparticles assembled as a shell over semimetal Te nanorod surfaces in acid electrolyte

Due to its interactions with semi-metallic Te nanorods, Ru nanoparticles assembled as a shell over Te nanorod surfaces (Te@Ru) formed an excellent catalyst for the hydrogen evolution reaction in an acid electrolyte solution.

Novel Cobalt-Doped Ni0.85Se Chalcogenides (Co xNi0.85- xSe) as High Active and Stable Electrocatalysts for Hydrogen Evolution Reaction in Electrolysis Water Splitting

In this paper, novel cobalt-doped Ni_0.85Se chalcogenides (Co _xNi_{0.85- x}Se, x = 0.05, 0.1, 0.2, 0.3, and 0.4) are successfully synthesized and studied as high active and stable electrocatalysts for hydrogen evolution reaction (HER) in electrolysis water splitting. The morphologies, structures, and composition of these as-prepared catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. The electrochemical tests, such as linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry testing, are performed to evaluate these catalysts' HER catalytic performance including activity and stability. The results indicate that a suitable doping can result in synergetic effect for increasing the catalytic performance. Among different catalysts, Co_0.1Ni_0.75Se shows the highest HER performance. After introducing the reduced graphene oxide (rGO) into this catalyst as the support, the resulted Co_0.1Ni_0.75Se/rGO shows even better performance than unsupported Co_0.1Ni_0.75Se, which are confirmed by the reduction of HER overpotential of Co_0.1Ni_0.75Se/rGO to 103 mV compared to 153 mV of Co_0.1Ni_0.75Se at a current density of 10 mA/cm², and the smaller Tafel slope (43 mV/dec) and kinetic resistance (21.34 Ω) than those of Co_0.1Ni_0.75Se (47 mV/dec, 30.23 Ω). Furthermore, the large electrochemical active surface area and high conductivity of such a Co_0.1Ni_0.75Se/rGO catalyst, induced by rGO introduction, are confirmed to be responsible for the high HER performance.

A comprehensive approach providing a new synthetic route for bimetallic electrocatalysts via isoPOMs [M/Rh(Cp*)4W8O32] (M = Rh (1) and Ir (2))

Polyoxometalates (POMs) are highly versatile materials if paired with various conducting supports. We here present a new prospective approach for obtaining advanced electrocatalytic systems via POMs (1 and 2) nanostructured on Ni foam (NF) to give bimetallic nanohybrid composite materials M0.4Ni0.6/WO3 (M = Rh (3) or Ir (4)). By this pathway, two rare isopolyoctatungstate-based organometallic clusters [Hx(MCp*)4W8O32]·yH2O (in 1, M = Rh, x = 8, y = 23; in 2, M = Ir, x = 4, y = 17.33) have been synthesized via one-pot reactions using [Cp*MCl2]2 (Cp* = pentamethylcyclopentadienyl, M = Rh or Ir) and Na2WO4·2H2O in basic conditions. Compounds 1 and 2 were successfully nanostructured on the surface of commercially available NF and were thermally reduced to M0.4Ni0.6/WO3 (M = Rh (3) or Ir (4)) after annealing at 400 °C for 8 h in a 15% H2/N2 atmosphere. Electrodes modified with the POMs 3 and 4 exhibited remarkable HER activities in a 1 M KOH solution and achieved a current density of 10 mA cm-2 at low overpotentials of about 67 and 35 mV versus RHE, with Tafel slopes of 56 and 34 mV dec-1, respectively.

Electrochemical Hydrogen Evolution Reaction Efficiently Catalyzed by Ru2 P Nanoparticles

Developing alternatives to Pt catalysts is a prerequisite to cost-effectively produce hydrogen. Herein, we demonstrate Ru₂ P nanoparticles (without any doping and modifications) as a highly efficient Pt-like catalyst for the hydrogen evolution reaction (HER) in different pH electrolytes. On transferring the hexagonal close-packed crystal structure of Ru to the orthorhombic structure of Ru₂ P, a greatly improved catalytic activity and stability toward HER is found owing to Ru-P coordination. The electronic state change originates from the P-Ru bonding structures, which accounts for the HER activity improvement compared with Ru nanoparticles. Specifically, Ru₂ P nanoparticles can drive 10 mA cm^-2 at a very low overpotential of 55 mV, only 8 mV more than Pt/C in an acidic solution; and an extremely low overpotential of approximately 50 mV is needed in alkaline solution, about 20 mV less than the Pt/C catalyst. The Volmer-Tafel mechanism is indicated on Ru₂ P nanoparticles with the typical Tafel slope of 30 mV dec^-1 of Pt metal indicating a Pt-like catalytic ability. Ru₂ P is more active in the Ru-P family as H atoms prefer to adsorb on Ru atoms rather than on the P element according to theoretical calculations. Considering the low price of Ru (20 % of Pt), anti-corrosion ability in the electrolyte, and the safe and reliable fabrication approach, the powder Ru₂ P nanoparticles make an excellent HER catalyst with great promise for large-scale water electrolysis applications.

Electrochemical oxygen evolution reaction catalyzed by a novel nickel–cobalt-fluoride catalyst

The nickel–cobalt-fluoride catalyst is a kind of novel and efficient non-precious catalyst for the oxygen evolution reaction.