Partially oxidized inter-doped RuNi alloy aerogel for the hydrogen evolution reaction in both alkaline and acidic media

A facile reduction and doping process is employed with the supercritical ethanol drying method to form RuNi alloy aerogels. The optimized heterostructure comprising RuNi metal, RuO2, and NiO phases is synthesized through partial oxidation. When applied to the surface of Ni foam, the multiphase aerogels form a morphology of highly porous 0D colloidal aerogel networks on the surface. RuNi alloy-Ni foam oxidized at 350 °C (RuNi-350@NF) has an overpotential of 89 and 61 mV in 1 M KOH and 0.5 M H2SO4 media at 50 mA cm-2, as well as satisfactory long-term stability. Additionally, the Tafel slopes in alkaline and acidic media are found to be 34 and 30.9 mV dec-1, respectively. Furthermore, it exhibits long-term stability (35 h) in alkaline and acidic media at high current densities of 50 mA cm-2, respectively. This study presents a novel strategy for developing exceptionally efficient and free-standing 3D porous aerogel electrocatalysts with potential applications in hydrogen production.

RuZn NPs with electroactivity and oxidase-like property for dual-mode anti-cancer drug monitoring

6-mercaptopurine (6-MP) as the effective anti-cancer drug was used for the treatment of Crohn's disease and acute lymphoblastic leukaemia, but the response to maintenance therapy was variable with individual differences. In order to control the dosage and decrease the side effects of 6-MP, a sensitive and stable assay was urgently needed for 6-MP monitoring. Herein, RuZn NPs with electrochemical oxidation property and oxidase-like activity was proposed for dual-mode 6-MP monitoring. Burr-like RuZn NPs were prepared and explored to not only exhibit an electrochemical oxidation signal at 0.78 V, but also displayed excellent oxidase-like performances. RuZn NPs were utilized for the dual-mode monitoring of 6-MP, attributing to the formation of Ru-SH covalent bonding. The colorimetric method showed good linearity from 10 μM to 5 mM with the limit of detection (LOD) of 300 nM, while the electrochemical method provided a higher sensitivity with the LOD of 37 nM in range from 100 nM to 200 μM. This work provided a new way for the fabrication of dual-functional nanotags with electroactivity and oxidase-like property, and opened a dual-mode approach for the 6-MP detection applications with complementary and satisfactory results.

Electronic redistribution through the interface of MnCo2O4-Ni3N nano-urchins prompts rapid In situ phase transformation for enhanced oxygen evolution reaction

One of the most coveted objectives in the realm of energy conversion technologies is the development of highly efficient and economically viable electrocatalysts for the oxygen evolution reaction. The commercialization of such techniques has thus far been impeded by their slow response kinetics. One of the many ways to develop highly effective electrocatalysts is to judiciously choose a coupling interface that maximizes catalyst performance. In this study, the in situ electrochemical phase transformation of MnCo2O4-Ni3N into MnCo2O4-NiOOH is described. The catalyst has an exceptional overpotential of 224 mV to drive a current density of 10 mA cm-2. Strong interfacial contact is seen in the MnCo2O4-Ni3N catalyst, leading to a considerable electronic redistribution between the MnCo2O4 and Ni3N phases. This causes an increase in the valence state of Ni, which makes it an active site for the adsorption of *OH, O*, and *OOH (intermediates). This charge transfer facilitates the rapid phase transformation to form NiOOH from Ni3N. At a higher current density of 300 mA cm-2, the catalyst remained stable for a period of 140 h. DFT studies also revealed that the in situ-formed NiOOH on the MnCo2O4 surface results in superior OER kinetics compared to that of NiOOH alone.

Zn and Ni dual hydrogen evolution sites integrated onto CdS for effective photocatalytic hydrogen production

Effective and affordable photocatalysts play an important role in the cost reduction of solar hydrogen production through photocatalytic water splitting. In this research, a Zn²⁺ and Ni²⁺ modified carbon hydrogen evolution cocatalyst (ZnNi-C) were synthesized and immobilized onto the surface of CdS (CdS@ZnNi-C) for photocatalytic hydrogen evolution (PHE). The preparation used an ethylenediaminetetraacetic acid disodium (EDTA)-assisted method. The hydrogen evolution rate and apparent quantum efficiency (AQE) at 420 nm for an optimized CdS@ZnNi-C photocatalyst are15.7 mmol/h/g and 31.4 %, respectively. The rate is 2.4 times and 3.7 times greater than those of Zn²⁺ and Ni²⁺ modified carbon cocatalysts (Zn-C) and (Ni-C) on CdS (CdS@Zn-C) and (CdS@Ni-C), respectively. Density functional theory calculations indicate that the elevated catalytic performance of CdS@ZnNi-C is due to the co-anchored Zn²⁺ and Ni²⁺ in carbon layers that lead to a favorable Gibbs free energy (ΔG_H*) for hydrogen evolution. This approach is valuable for the design of stable and efficient photocatalysts for renewable hydrogen production.

Hydrogen evolution reaction catalysis on RuM (M = Ni, Co) porous nanorods by cation etching

The development of efficient and stable nanomaterial electrocatalysts for the hydrogen evolution reaction (HER) is of great significance for renewable energy conversion via water electrolysis. Herein, we have developed a novel class of bimetallic RuM (M = Ni, Co) hollow nanorods (HNRs) through a facile Fe³⁺ etching strategy, as electrocatalysts for enhancing the HER. Morphological physical characterization and electrochemical tests demonstrated that RuM (M = Ni, Co) HNRs with hollow structures can effectively enhance electrocatalytic activity due to their high specific surface areas. Impressively, the RuNi HNRs exhibited superior HER performance with an overpotential of merely 25.6 mV in 1 M KOH solution at 10 mA cm^-2, which is significantly lower than that of commercial Pt/C (44.7 mV). Moreover, the as prepared RuNi HNRs showed excellent stability and could continuously work at a current density of 10 mA cm^-2 for 40 h with a negligible increase in potential. The Ru-based HNRs also showed high HER activity in an acidic solution. This study paves a new way for the universal fabrication of bimetallic hollow structured nanomaterials as efficient electrocatalysts for boosting the HER.

Urchin-like hierarchical ruthenium cobalt oxide nanosheets on Ti3C2Tx MXene as a binder-free bifunctional electrode for overall water splitting and supercapacitors

Synthesizing efficient electrode materials for water splitting and supercapacitors is essential for developing clean electrochemical energy conversion/storage devices. In the present work, we report the construction of a ruthenium cobalt oxide (RuCo₂O₄)/Ti₃C₂T_x MXene hybrid by electrophoretic deposition of Ti₃C₂T_x MXene on nickel foam (NF) followed by RuCo₂O₄ nanostructure growth through an electrodeposition process. Owing to the strong interactions between RuCo₂O₄ and Ti₃C₂T_x sheets, which are verified by density functional theory (DFT)-based simulations, RuCo₂O₄/Ti₃C₂T_x MXene@NF can serve as a bifunctional electrode for both water splitting and supercapacitor applications. This electrode exhibits outstanding electrocatalytic activity with low overpotentials of 170 and 68 mV at 100 A m^-2 toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The RuCo₂O₄/Ti₃C₂T_x MXene@NF-based alkaline water-splitting cell only requires 1.62 V to achieve a current density of 100 A m^-2, which is much better than that of RuO₂@NF and Pt/C@NF-assembled cells (1.75 V@100 A m^-2). The symmetric supercapacitor (SSC)-assembled electrode displays a high specific capacitance of 229 F g^-1 at 3 A g^-1. The experimental results, complemented with theoretical insights, provide an effective strategy to prepare multifunctional materials for electrocatalysis and energy storage applications.

Increased crystallinity of RuSe2/carbon nanotubes for enhanced electrochemical hydrogen generation performance

Ru-Based catalysts are significant in the green hydrogen generation via the electrochemical water-splitting reaction. Herein, it is found that the increased crystallinity of cubic RuSe₂ nanoparticles anchored over carbon nanotubes (RuSe₂/CNTs) could largely increase the hydrogen generation performance both in acidic and alkaline electrolytes. The freshly prepared RuSe₂/CNTs with low crystallinity had a very low catalytic performance for the HER, while the catalytic ability could be largely boosted by facile thermal annealing at 650 °C in an N₂ atmosphere, resulting from the increased crystallinity and electronic effect. The crystal structure enhancement of the RuSe₂ nanoparticles was well supported by the X-ray diffraction technique and the lattice fringes in the high-resolution transmission electron microscopy images. As a result, the catalyst exhibited largely improved catalytic performance compared to the freshly prepared RuSe₂/CNTs; specifically, the overpotentials of 48 and 64 mV were required to drive 10 mA cm^-2 in alkaline and acidic media when loaded on a glassy carbon electrode, much less than those of 109 and 120 mV for the freshly prepared RuSe₂/CNTs; the catalytic performance in the alkaline electrolyte was even close to that of the commercial Pt/C catalyst. Correspondingly, the improved catalytic stability, catalytic kinetics, charge transfer ability and catalytic efficiency of the active sites were also observed. The current work shows an effective approach and important understanding for catalytic performance enhancement via increased crystallinity by facile thermal annealing.

Manipulating Ru oxidation within electrospun carbon nanofibers to boost hydrogen and oxygen evolution for electrochemical overall water splitting

1D bifunctional RuO2/Ru-CNFs-350 catalyst is fabricated to show high activity and remarkable durability toward both OER and HER due to the formation of a RuO2/Ru heterostructure and the carbon substrate.

Vanadium-Doping and Interface Engineering for Synergistically Enhanced Electrochemical Overall Water Splitting and Urea Electrolysis

Fabricating effective non-precious metal-based catalysts for hydrogen production via electrochemical water splitting is of considerable importance but remains challenging. Transition metal nitrides possessing metallic character and corrosion resistance have been considered as potential replacements for precious metals. However, their activities for water electrolysis are impeded by the strong hydrogen adsorption and low water adsorption energies. Herein, V-doped bimetallic nitrides, V-FeNi₃N/Ni₃N heterostructure, are synthesized via a hydrothermal-nitridation protocol and used as electrocatalysts for water splitting and urea electrolysis. The V-FeNi₃N/Ni₃N electrode exhibits superior HER and OER activities, and the overpotentials are 62 and 230 mV to acquire a current density of 10 mA cm^-2, respectively. Moreover, as a bifunctional electrocatalyst for overall water splitting, a two-electrode device needs a voltage of 1.54 V to reach a current density of 10 mA cm^-2. The continuous electrolysis can be run for more than 120 h, surpassing most previously reported electrocatalysts. The excellent performance for water electrolysis is dominantly due to V-doping and interface engineering, which could enhance water adsorption and regulate the adsorption/desorption of intermediates species, thereby accelerating HER and OER kinetic processes. Besides, a urea-assisted two-electrode electrolyzer for electrolytic hydrogen production requires a cell voltage of 1.46 V at 10 mA cm^-2, which is 80 mV lower than that of traditional water electrolysis.

Ethylene Glycol Electrochemical Reforming Using Ruthenium Nanoparticle-Decorated Nickel Phosphide Ultrathin Nanosheets

In this work, ruthenium nanoparticle-decorated ultrathin nickel phosphide nanosheets on nickel foam substrate (Ru/Ni₂P/NF) nanocomposites are synthesized conveniently by a cyanogel-NaBH₄ method and a subsequent phosphating process, which displays excellent electroactivity for both the hydrogen evolution reaction (HER) and ethylene glycol electro-oxidation reaction (EGEOR) in an alkaline solution. Concretely, at Ru/Ni₂P/NF nanocomposites, only 1.37 and -0.13 V potentials are required to obtain a current density of 100 mA cm^-2 for EGEOR and HER, respectively. Meanwhile, Ru/Ni₂P/NF nanocomposites also exhibit pre-eminent electrocatalytic performance of the long-running process for both EGEOR and HER. Density functional theory calculations demonstrate that the introduction of Ru nanoparticles results in an optimization of the surface adsorption energy and construction of a synergistic catalysis interface, which improve the electrocatalytic performance of nickel phosphide nanosheets. Notably, a symmetric Ru/Ni₂P/NF||Ru/Ni₂P/NF ethylene glycol electrolyzer needs only 1.14 V electrolysis voltage to obtain 10 mA cm^-2 for hydrogen production, which effectively eliminates the H₂/O₂ explosion risk and highlights an energy-saving mode for electrochemical hydrogen production.

General fabrication of RuM (M = Ni and Co) nanoclusters for boosting hydrogen evolution reaction electrocatalysis

Rational design and fabrication of highly active electrocatalysts toward the hydrogen evolution reaction (HER) are of paramount significance in industrial hydrogen production via water electrolysis. Herein, by taking advantage of the high surface-to-volume ratio, maximized atom-utilization efficiency, and quantum size effect, we have successfully fabricated an innovative class of Ru-based alloy nanoclusters. Impressively, carbon fiber cloth (CFC) supported RuNi nanoclusters could exhibit outstanding electrocatalytic performance toward the HER, in which the optimal composition RuNi/CFC could achieve a current density of 10 mA cm^-2 with an overpotential of merely 43.0 mV in 1 M KOH electrolyte, as well as a low Tafel slope of 30.4 mF dec^-1. In addition to the high HER activity in alkaline media, such Ru-based alloy nanoclusters are also demonstrated to be highly active and stable in acidic solution. Mechanistic studies reveal that the alloying effect facilitates water dissociation and optimizes hydrogen adsorption and desorption, thereby contributing to the outstanding HER performance. This work paves a new way for the rational fabrication of advanced electrocatalysts for boosting the HER.

The template synthesis of ultrathin metallic Ir nanosheets as a robust electrocatalyst for acidic water splitting

Ultrathin metallic iridium nanosheets (∼4 nm) were synthesized using MIL-88A as the sacrificing template at room temperature. Ir-NS shows superior and stable water splitting performance in an acidic medium.

3D Porous Ru-Doped NiCo-MOF Hollow Nanospheres for Boosting Oxygen Evolution Reaction Electrocatalysis

Developing high-performance and cost-efficient catalysts toward oxygen evolution reaction (OER) is an important but daunting task due to the sluggish kinetics hindered by the four-electron transfer process. Herein, an advanced class of ultralow Ru-doped NiCo-MOF hollow porous nanospheres (denoted as Ru@NiCo-MOF HPNs) has been reported in this work. Benefiting from the high porosity and large surface area of the metal-organic frameworks (MOFs) and optimized electronic properties by Ru doping, the as-prepared Ru@NiCo-MOF HPNs exhibit superior performance for water oxidation with the overpotential of only 284 mV to reach a current density of 10 mA·cm^-2 in alkaline electrolyte, as well as a small Tafel slope of 78.8 mV·dec^-1, outperforming the NiCo-MOF HPNs (358 mV) and commercial RuO₂ catalyst (326 mV). The incorporation of Ru in NiCo-MOF HPNs enables a stable OER activity for at least 39 h. Moreover, we have probed the interaction between the content of Ru and OER performance, impressively, Ru@NiCo-MOF HPNs with 13.5 atom % Ru doping (denoted as Ru@NiCo-MOF-4) exhibited the highest OER activity with the excellent mass activity of 310 mA·mg^-1 at an overpotential of 284 mV. Besides, a two-electrode cell with Ru@NiCo-MOF-4 as the anode and commercial Pt/C catalyst as the cathode also demonstrated outstanding electrocatalytic overall water splitting performance with a cell potential of merely 1.57 V to deliver a current density of 10 mA·cm^-2.

Nanostructured RuO2-Co3O4@RuCo-EO with low Ru loading as a high-efficiency electrochemical oxygen evolution catalyst

Electrochemical water splitting technology is considered to be the most reliable method for converting renewable energy such as wind and solar energy into hydrogen. Here, a nanostructured RuO₂/Co₃O₄–RuCo-EO electrode is designed via magnetron sputtering combined with electrochemical oxidation for the oxygen evolution reaction (OER) in an alkaline medium. The optimized RuO₂/Co₃O₄–RuCo-EO electrode with a Ru loading of 0.064 mg cm⁻² exhibits excellent electrocatalytic performance with a low overpotential of 220 mV at the current density of 10 mA cm⁻² and a low Tafel slope of 59.9 mV dec⁻¹ for the OER. Compared with RuO₂ prepared by thermal decomposition, its overpotential is reduced by 82 mV. Meanwhile, compared with RuO₂ prepared by magnetron sputtering, the overpotential is also reduced by 74 mV. Furthermore, compared with the RuO₂/Ru with core–shell structure (η = 244 mV), the overpotential is still decreased by 24 mV. Therefore, the RuO₂/Co₃O₄–RuCo-EO electrode has excellent OER activity. There are two reasons for the improvement of the OER activity. On the one hand, the core–shell structure is conducive to electron transport, and on the other hand, the addition of Co adjusts the electronic structure of Ru.

The optimized RuO₂/Co₃O₄–RuCo-EO electrode with Ru loading of 0.064 mg cm⁻² exhibits the excellent oxygen evolution activity with an overpotential of 220 mV at the current density of 10 mA cm⁻² and a Tafel slope of 59.9 mV dec⁻¹.

Co-Doped Ni3N Nanosheets with Electron Redistribution as Bifunctional Electrocatalysts for Efficient Water Splitting

Preparation of high-activity and earth-abundant bifunctional catalysts for efficient electrochemical water splitting are crucial and challenging. Herein, Co-doped Ni₃N nanosheets loaded on nickel foam (Co-Ni₃N) were synthesized. The as-prepared Co-Ni₃N exhibits excellent catalytic activity toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline media. Density functional theory (DFT) calculation reveals that Co-Ni₃N with redistribution of electrons not only can facilitate the HER kinetics but also can regulate intermediates adsorption energies for OER. Specifically, the Co-Ni₃N exhibits high efficiency and stable catalytic activity, with an overpotential of only 30 and 270 mV at a current density of 10 mA cm^-2 for the HER and OER in 1 M KOH, respectively. This work provides strong evidence to the merit of Co doping to improve the innate electrochemical performance in bifunctional catalysts, which might have a common impact in many similar metal-metal nitride electrocatalysts.

Nonlayered 2D ultrathin molybdenum nitride synthesized through the ammonolysis of 2D molybdenum dioxide

We report a new scalable strategy for the synthesis of nonlayered ultrathin two-dimensional (2D) molybdenum nitride (MoN) on a SiO₂/Si substrate by converting 2D molybdenum dioxide (MoO₂) through an ammonolysis process. The edge of MoN shows higher performance than that of the basal plane in both acidic and alkaline solutions.

Nb-Doped nickel nitride-derived catalysts for electrochemical water splitting

An alkaline electrolyzer using Nb-doped nickel nitride-derived catalysts as electrodes for overall water splitting delivers 10 mA cm−2 at a low cell voltage of 1.61 V.

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.

Construction of FeCo2O4@N-Doped Carbon Dots Nanoflowers as Binder Free Electrode for Reduction and Oxidation of Water

Electrochemical water splitting is known as a potential approach for sustainable energy conversion; it produces H₂ fuel by utilizing transition metal-based catalysts. We report a facile synthesis of FeCo₂O₄@carbon dots (CDs) nanoflowers supported on nickel foam through a hydrothermal technique in the absence of organic solvents and an inert environment. The synthesized material with a judicious choice of CDs shows superior performance in hydrogen and oxygen evolution reactions (HER and OER) compared to the FeCo₂O₄ electrode alone in alkaline media. For HER, the overpotential of 205 mV was able to produce current densities of up to 10 mA cm⁻², whereas an overpotential of 393 mV was needed to obtain a current density of up to 50 mA cm⁻² for OER. The synergistic effect between CDs and FeCo₂O₄ accounts for the excellent electrocatalytic activity, since CDs offer exposed active sites and subsequently promote the electrochemical reaction by enhancing the electron transfer processes. Hence, this procedure offers an effective approach for constructing metal oxide-integrated CDs as a catalytic support system to improve the performance of electrochemical water splitting.

Oxygen-evolution reaction by nickel/nickel oxide interface in the presence of ferrate(VI)

In this study, we investigate the effect of K2FeO4, as a new and soluble Fe salt at alkaline conditions, on oxygen-evolution reaction (OER) of Ni oxide. Both oxidation and reduction peaks for Ni in the presence and absence of Fe are linearly changed by (scan rate)1/2. Immediately after the interaction of [FeO4]2- with the surface of the electrode, a significant increase in OER is observed. This could be indicative of the fact that either the [FeO4]2- on the surface of Ni oxide is directly involved in OER, or, it is important to activate Ni oxide toward OER. Due to the change in the Ni(II)/(III) peak, it is hypothesized that Fe impurity in KOH or electrochemical cell has different effects at the potential range. At low potential, [FeO4]2- is reduced on the surface of the electrode, and thus, is significantly adsorbed on the electrode. Finally, oxygen-evolution measurements of K2FeO4 and Ni2O3 are investigated under chemical conditions. K2FeO4 is not stable in the presence of Ni(II) oxide, and OER is observed in a KOH solution (pH ≈ 13).

Synergistically boosting the oxygen evolution reaction of an Fe-MOF via Ni doping and fluorination

An efficient approach to boost the oxygen evolution activity of Fe-MOF nanorods was demonstrated by a synergistic strategy of Ni doping and fluorination.