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

Fabrication of Ru-doped CuMnBP micro cluster electrocatalyst with high efficiency and stability for electrochemical water splitting application at the industrial-level current density

Electrochemical water splitting has been considered as a key pathway to generate environmentally friendly green hydrogen energy and it is essential to design highly efficient electrocatalysts at affordable cost to facilitate the redox reactions of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this work, a novel micro-clustered Ru/CuMnBP electrocatalyst is introduced, prepared via hydrothermal deposition and soaking-assisted Ru doping approaches on Ni foam substrate. Ru/CuMnBP micro-clusters exhibit relatively low HER/OER turnover overpotentials of 11 mV and 85 mV at 10 mA/cm2 in 1 M KOH. It also demonstrates a low 2-E turnover cell voltage of 1.53 V at 10 mA/cm2 for the overall water-splitting, which is comparable with the benchmark electrodes of Pt/C||RuO2. At a super high-current density of 2000 mA/cm2, the dual functional Ru/CuMnBP demonstrates an exceptionally low 2-E cell voltage of 3.13 V and also exhibits superior stability for over 10 h in 1 M KOH. Excellent electrochemical performances originate from the large electrochemical active surface area with the micro cluster morphology, high intrinsic activity of CuMnBP micro-clusters optimized through component ratio adjustment and the beneficial Ru doping effect, which enhances active site density, conductivity and stability. The usage of Ru in small quantities via the simple soaking doping approach significantly improves electrochemical reaction rates for both HER and OER, making Ru/CuMnBP micro-clusters promising candidates for advanced electrocatalytic applications.

Phytochemical-enhanced NiO nanostructures for superior oxygen evolution and asymmetric supercapacitor applications

The development of new energy conversion and storage technologies has contributed to the widespread use of renewable energy. However, new methodologies for electrochemical energy storage systems remain to be developed. This study presents a facile, low-cost, scalable, and environmentally friendly method for the synthesis of nickel oxide (NiO) nanostructures by hydrothermal methods using lotus root extract. The different volumes of lotus root extract were tested on NiO nanostructures (sample 1, sample 2) using 1 ml and 2 ml amounts of the extract, respectively. Therefore, phytochemicals from lotus extract have influenced the surface morphology, crystal quality, optical band gap, electrical conductivity, and surface active sites of NiO nanostructures. Sample 2 of the NiO nanostructures was found to be highly active for oxygen evolution reaction (OER) and showed an overpotential of 380 mV at 10 mA cm−2 and a durability of 30 h at 10 mA cm−2. Furthermore, sample 2 of NiO has shown specific capacitance of 1503.84 F g−1 at 2 A g−1 as well as cycling stability over a period of forty thousand GCD cycles. The percentage specific capacitance retention were highly improved up to 100.6%. An asymmetric energy storage device has been constructed using NiO sample 2 as the anode electrode material, demonstrating excellent specific capacity of about 1113 C g−1 at 5 A g−1. For the asymmetric supercapacitor device, a power density of 20000 W kg−1 and an energy density of 245 Wh kg−1 were obtained. In a study of cycling stability for 40000 GCD cycles, it was observed that the asymmetric device retained 96.86% of its specific capacitance. A significant contribution was made to the electrochemical performance of sample 2 of NiO by phytochemicals derived from lotus extract.

Ru doping and interface engineering synergistically boost the electrocatalytic performance of a WP/WP2 nanosheet array for an efficient hydrogen evolution reaction

The surface electronic structure and morphology of catalysts have a crucial impact on the electrocatalytic hydrogen evolution reaction performance. This work reports on the fabrication of a Ru-doped WP/WP2 heterojunction nanosheet array electrode via a one-step phosphating treatment of a Ru-doped WO3 precursor. Benefitting from the large electrochemical active surface of nanosheet arrays, rich WP/WP2 heterojunction interface, and trace Ru atom doping, the catalyst has a fairly low overpotential of 58.0 mV at 10 mA cm-2 and a Tafel slope of 50.71 mV dec-1 in acid solution toward the electrocatalytic HER. Further, theoretical calculations unveil that Ru atom doping and interface effect synergistically optimized the electronic structure of the catalyst and hence weakened the adsorption capacity of the catalyst surface toward hydrogen (H), which lowered the Gibbs free energy (ΔGH*) and consequently effectively improved the HER performance. This work may open new avenues for developing advanced nanoarray electrodes with efficient electrochemical energy conversion.

Metal-Organic Framework (MOF)-Based Clean Energy Conversion: Recent Advances in Unlocking its Underlying Mechanisms

Carbon neutrality is an important goal for humanity . As an eco-friendly technology, electrocatalytic clean energy conversion technology has emerged in the 21st century. Currently, metal-organic framework (MOF)-based electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), carbon dioxide reduction reaction (CO2RR), nitrogen reduction reaction (NRR), are the mainstream energy catalytic reactions, which are driven by electrocatalysis. In this paper, the current advanced characterizations for the analyses of MOF-based electrocatalytic energy reactions have been described in details, such as density function theory (DFT), machine learning, operando/in situ characterization, which provide in-depth analyses of the reaction mechanisms related to the above reactions reported in the past years. The practical applications that have been developed for some of the responses that are of application values, such as fuel cells, metal-air batteries, and water splitting have also been demonstrated. This paper aims to maximize the potential of MOF-based electrocatalysts in the field of energy catalysis, and to shed light on the development of current intense energy situations.

In-situ reconstruction of rock-like 3D hierarchical MIL-53(Fe) self-supporting electrode with oxygen vacancy induced ultra-long stable and efficient water oxidation

The exploitation of efficient, stable and cheap electrocatalyst for oxygen evolution reaction (OER) is very significant to the development of energy technology. In this study, Fe-based metal-organic frameworks (MIL-53(Fe)) self-supporting electrode with a 3D hierarchical open structure was developed through a semi-sacrificial strategy. The self-supporting electrode exhibits an excellent OER performance with an overpotential of 328 mV at 100 mA cm-2 in 1 M KOH, which is superior than that of IrO2 catalyst. Importantly, the optimized self-supporting electrode could operate at 100 mA cm-2 for 520 h without visible decrease in activity. It was also found that the structure of MIL-53(Fe) was in-situ self-reconstructed into oxyhydroxides during OER process. However, the 3D hierarchical open structure assembled with nano-microstructures kept well, which ensured the long-term stability of our self-supporting electrode for OER. Furthermore, density functional theory (DFT) calculations reveal that the FeOOH with rich oxygen vacancy transformed from MIL-53(Fe) plays a key role for the OER catalytic activity. And, the uninterrupted formation of oxygen vacancy during OER process ensures the continuous OER catalytic activity, which is the original source for the ultra-long stability of the self-supporting electrode toward OER. This work explores the way for the construction of efficient self-supporting oxygen electrodes based on MOFs.

Unleashing the room temperature boronization: Blooming of Ni-ZIF nanobuds for efficient photo/electro catalysis of water

Water splitting provides an environmental-friendly and sustainable approach for generating hydrogen fuel. The inherent energetic barrier in two-core half reactions such as the Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) leads to undesired increased overpotential and constrained reaction kinetics. These challenges pose significant challenges that demand innovative solutions to overcome. One of the efficient ways to address this issue is tailoring the morphology and crystal structure of metal-organic frameworks (MOF). Nickel Zeolite Imidazolate Framework (Ni-ZIF) is a popular MOF and it can be tailored using facile chemical methods to unleash a remarkable bifunctional electro/photo catalyst. This innovative solution holds the capability to address prevailing obstacles such as inadequate electrical conductivity and limited access to active metal centers due to the influence of organic ligands. Thereby, applying boronization to the Ni-ZIF under different duration, one can induce blooming of nanobuds under room temperature and modify oxygen vacancies in order to achieve higher reaction kinetics in electro/photo catalysis. It can be evidenced by the 24-h boronized Ni-ZIF (BNZ), exhibiting lower overpotentials as electrocatalyst (OER-396 mV & HER-174 mV @ 20 mA/cm2) in 1 M KOH electrolyte and augmented gas evolution rates when employed as a photocatalyst (Hydrogen-14.37 μmol g-1min-1 & Oxygen-7.40 μmol g-1min-1). The 24-h boronization is identified as the optimum stage of crystalline to amorphous transformation which provided crystalline/amorphous boundaries as portrayed by X-Ray diffraction (XRD) and High Resolution-Transmission Electron Microscopy (HR-TEM) analysis. The flower-like transformation of 24-BNZ, characterized by crystalline-amorphous boundaries initiates with partial disruption of Ni-N bonds and formation of Ni-B bonds as evident from X-ray Photoelectron Spectroscopy (XPS). Further, the 24-h BNZ exhibit bifunctional catalytic activities with pre-longed stability. Overall, this work presents a comprehensive study of the electrocatalytic and photocatalytic water splitting properties of the tailored Ni-ZIF material.

Metal-Organic-Framework-Based Nanoarrays for Oxygen Evolution Electrocatalysis

The development of highly active and stable electrode materials for the oxygen evolution reaction (OER) is essential for the widespread application of electrochemical energy conversion systems. In recent years, various metal-organic frameworks (MOFs) with self-supporting array structures have been extensively studied because of their high porosity, abundant metal sites, and flexible and adjustable structures. This review provides an overview of the recent progress in the design, preparation, and applications of MOF-based nanoarrays for the OER, beginning with the introduction of the architectural advantages of the nanoarrays and the characteristics of MOFs. Subsequently, the design principles of robust and efficient MOF-based nanoarrays as OER electrodes are highlighted. Furthermore, detailed discussions focus on the composition, structure, and performance of pristine MOF nanoarrays (MOFNAs) and MOF-based composite nanoarrays. On the one hand, the effects of the two components of MOFs and several modification methods are discussed in detail for MOFNAs. On the other hand, the review emphasizes the use of MOF-based composite nanoarrays composed of MOFs and other nanomaterials, such as oxides, hydroxides, oxyhydroxides, chalcogenides, MOFs, and metal nanoparticles, to guide the rational design of efficient OER electrodes. Finally, perspectives on current challenges, opportunities, and future directions in this research field are provided.

Ultralow ruthenium modification of cobalt metal-organic frameworks for enhanced efficient bifunctional water splitting

Hydrogen economy has emerged as a promising alternative to the current hydrocarbon economy. It involves harvesting renewable energy to split water into hydrogen and oxygen and then further utilising clean hydrogen fuel for various applications. The rational exploration of advanced non-precious metal bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is critical for efficient water splitting. Herein, an ultralow Ru-modified cobalt metal-organic framework (CoRu0.06-MOF/NF) two-dimensional nanosheet array bifunctional catalyst was fabricated through a strategy under mild experimental conditions. The obtained CoRu0.06-MOF/NF exhibited excellent bifunctional electrocatalytic activity and stability in alkaline media, with low overpotentials of 37 and 181 mV and significant durability for more than 95 and 110 h toward the HER and OER at 10 mA cm-2, respectively. The experimental results showed that the two-dimensional nanoarray structure had a large specific surface area and abundant exposed active sites. Additionally, ultralow Ru modification optimized the electronic structure and improved the conductivity of the cobalt metal-organic frameworks, thereby reducing the energy barrier of the rate-limiting step and accelerating the water splitting reaction.

Electronic interaction of ruthenium species on bimetallic phosphide for superior electrocatalytic hydrogen generation

The exploitation of high-performance electrocatalysts to achieve the economic electrocatalytic hydrogen evolution reaction (HER) is significant in generating H2 fuel. Enhancing the activity of the carrier catalyst by modifying trace precious metals is one of the important strategies. Herein, a hybrid material is developed by incorporating trace Ru species into a bimetallic phosphide (NiCoP) matrix on nickel foam (NF), showing a superior catalytic activity for HER. The Ru-NiCoP/NF hybrid material has plenty of heterointerfaces, improved electronic interaction, and small interfacial charge transfer resistance, improving the reaction kinetics of the HER. Remarkable, the Ru-NiCoP/NF provides a low overpotential of 96 mV at the current density of 50 mA cm-2 and high stability in 1.0 M KOH solution presenting a promising potential for hydrogen production. In addition, the Ru-NiCoP/NF sample exhibits the highest TOF value of 0.54 s-1 at an overpotential of 100 mV, which outperforms the commercial Ru/C catalyst. This study offers a promising approach for the synthesis of other precious metal supported hybrid materials.

A Unique Etching-Doping Route to Fe/Mo Co-Doped Ni Oxyhydroxide Catalyst for Enhanced Oxygen Evolution Reaction

Fe-doped Ni (oxy)hydroxide shows intriguing activity toward oxygen evolution reaction (OER) in alkaline solution, yet it remains challenging to further boost its performance. In this work, a ferric/molybdate (Fe3+ /MoO4 2- ) co-doping strategy is reported to promote the OER activity of Ni oxyhydroxide. The reinforced Fe/Mo-doped Ni oxyhydroxide catalyst supported by nickel foam (p-NiFeMo/NF) is synthesized via a unique oxygen plasma etching-electrochemical doping route, in which precursor Ni(OH)2 nanosheets are first etched by oxygen plasma to form defect-rich amorphous nanosheets, followed by electrochemical cycling to trigger simultaneously Fe3+ /MoO4 2- co-doping and phase transition. This p-NiFeMo/NF catalyst requires an overpotential of only 274 mV to reach 100 mA cm-2 in alkaline media, exhibiting significantly enhanced OER activity compared to NiFe layered double hydroxide (LDH) catalyst and other analogs. Its activity does not fade even after 72 h uninterrupted operation. In situ Raman analysis reveals that the intercalation of MoO4 2- is able to prevent the over-oxidation of NiOOH matrix from β to γ phase, thus keeping the Fe-doped NiOOH at the most active state.

Corrosion Engineering towards NiFe-Layered Double Hydroxide Macroporous Arrays with Enhanced Activity and Stability for Oxygen Evolution Reaction

NiFe-layered double hydroxide (NiFe-LDH) is the benchmark catalyst for the oxygen evolution reaction (OER) in alkaline medium, however, it is still challenging to improve its activity and stability. Herein, NiFe-LDH macroporous array electrodes are demonstrated to significantly enhance the activity and stability for oxygen evolution reaction. The electrodes are fabricated by the chemical and electrochemical corrosion process of Ni foam induced by ferric nitrate, hydrochloric acid and oxygen. By optimizing the amount of iron salt and acid and selecting the appropriate reaction temperature and time, the NiFe-LDH electrodes only need the overpotential of 180 mV and 248 mV to reach the current density of 10 mA cm-2 and 500 mA cm-2 , respectively, and remain highly stable for 1000 h at 500 mA cm-2 . The unique macroporous array not only significantly increases the active area of NiFe-LDH catalyst, but also creates a stable nanostructure that avoids severe reconstruction.

Coupling Transition Metal Catalysts with Ir for Enhanced Electrochemical Water Splitting Activity

Developing advanced electrocatalysts is of great significance for boosting electrochemical water splitting to produce hydrogen. The electrocatalytic activity of a catalyst is associated with the surface/interface, geometric structure, and electronic properties. Coupling Ir with transition metal compounds is an effective strategy to improve their electrocatalytic performance. In this review, we summarize the recent progress of Ir coupled transition metal compound catalysts for the application in driving electrochemical water splitting. The significant role of Ir played in the promotion of electrocatalytic performance is firstly illustrated. Then, the applications of Ir-based catalysts in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are comprehensively discussed, with an emphasis on correlating the structure-function relationships. Lastly, the challenges and future directions for the fabrication of more advanced Ir coupled electrocatalysts are also presented.

Active Sites In Situ Implanted Hybrid Zeolitic Imidazolate Frameworks for a Water Oxidation Catalyst

Metal-organic frameworks (MOFs) have been a focus of research because of their unique porous structure, but they are usually not directly for electrocatalysis. Herein, we prepared a special class of Fe/Zn/Mo-based trimetallic hybrid zeolitic imidazolate frameworks by in situ solvothermal synthesis that have the potential to act directly as highly efficient oxygen evolution reaction electrocatalysts. This work provides a foundation for the preparation of multimetal MOFs and expands the investigation of electrocatalysts.

Acetate promotes the formation of NiRu/NiO towards efficient hydrogen evolution

The introduction of acetate in the precursor of metal-organic frameworks (MOFs) turns the final product from MOFs to NiRu/Ni(OH)₂. Followed by annealing treatment, the obtained NiRu/NiO catalyst exhibits high hydrogen evolution reaction (HER) activity with a low overpotential (18 mV at 10 mA cm^-2), and a small Tafel slope of 43.3 mV dec^-1 in alkaline electrolyte.

Ru doping boosts electrocatalytic water splitting

Heteroatom doping plays a crucial role in improving the electrocatalytic performance of catalysts towards water splitting. Owing to the existence of Ru-O moieties, Ru is thus emerging as an ideal dopant for promoting the electrocatalytic performance for water splitting by modifying the electronic structure, introducing extra active sites, improving electronic conductivity, and inducing a strong synergistic effect. Benefitting from these advantages, Ru-doped nanomaterials have been widely investigated and employed as advanced electrocatalysts for water splitting, and many excellent Ru-doped electrocatalysts have been successfully developed. In an effort to obtain a better understanding of the influence of Ru doping on the electrocatalytic water splitting performance of nanocatalysts, we herein summarize the recent progress of Ru-doped electrocatalysts by focusing on the synthesis strategies and advantageous merits. Applications of these new materials in water electrolysis technology are also discussed with emphasis on future directions in this active field of research.

In situ growth of hierarchical bimetal-organic frameworks on nickel-iron foam as robust electrodes for the electrocatalytic oxygen evolution reaction

Evidence shows that self-supported electrocatalysts are crucial role to solving environmental and energy issues. In this study, self-supported 2D metal-organic framework (MOF) nanosheets grown in situ on nickel-iron foam (NFF) were prepared by a one-step solvothermal process. The hierarchical nanostructure possesses a high specific surface area and abundant metal sites, which are beneficial for electrocatalytic reactions. In the electrocatalytic oxygen evolution reaction (OER), the optimal NiFe(20Ni)-MOF/NFF can drive current densities of 10, 50 and 100 mA cm^-2 at small overpotentials of 226, 277 and 294 mV, respectively. According to the characterization results, the OER performance is improved by the synergistic action of bimetals and the generation of hydroxides/oxyhydroxides. This work provides new insights into fabricating self-supported MOF-based electrodes for water splitting that are simple and highly efficient.

Highly Dispersed Ru Nanoclusters Anchored on B, N Co-doped Carbon Nanotubes for Water Splitting

We developed an N, B co-doped carbon nanotubes as a substrate material to load 2-3 nm uniform Ru clusters. We rationally realized controllable N and B doping into carbon nanotubes....

Plasma-assisted rhodium incorporation in nickel–iron sulfide nanosheets: enhanced catalytic activity and the Janus mechanism for overall water splitting

Rh was incorporated in Fe-doped Ni3S2 nanosheets with the assistance of hydrogen plasma to significantly enhance the HER/OER catalytic activity. The operando evolution behavior and Janus catalytic mechanism of this catalyst were further revealed.

Ru doping NiCoP hetero-nanowires with modulated electronic structure for efficient overall water splitting

Herein, a novel Ru-doped bimetal phosphide (Ru-NiCoP) heterostructure electrocatalyst on Ni foam is successfully synthesized through a multi-step hydrothermal reaction, ion exchange, and phosphorization method for efficient overall water splitting in alkaline media. The doping of Ru and P can effectively optimize the electronic structure and expose more active sites. The unique 3D interconnected nanowires not only ensures the uniform distribution of Ru coupled with NiCoP, but also endows the Ru-NiCoP/NF with the large ECSA, the fast electron transport and the favorable reaction kinetics attributes. Benefiting from the compositional and structural advantages, Ru-NiCoP/NF catalyst exhibits significantly enhancedcatalytic activities along with excellent stability, only needing 32.3 mV at 10 mA cm^-2 for HER and 233.8 mV at 50 mA cm^-2 for OER. In particular, when Ru-NiCoP/NF is employed as both cathode and anode electrodes,a small voltage of 1.50 V is required to reach 30 mA cm^-2for overall water splittingwith an impressive stability. This study provides an alternative strategyon the design and development of high performance catalysts foroverall water splittingand other energy conversion fields.

Recent Developments for the Application of 3D Structured Material Nickel Foam and Graphene Foam in Direct Liquid Fuel Cells and Electrolyzers

Platinum and platinum-based catalysts are some of the most effective catalysts used in fuel cells. However, electrocatalysts used for direct liquid fuel cells (DLFCs) and electrolyzers are high cost and suffer from several other problems, thus hindering their commercialization as power sources to produce clean energy. Common issues in electrocatalysts are low stability and durability, slow kinetics, catalyst poisoning, high catalyst loading, high cost of the catalytic materials, poisoning of the electrocatalysts, and formation of intermediate products during electrochemical reactions. The use of catalyst supports can enhance the catalytic activity and stability of the power sources. Thus, nickel foam and graphene foam with 3D structures have advantages over other catalyst supports. This paper presents the application of nickel foam and graphene foam as catalyst supports that enhance the activities, selectivity, efficiency, specific surface area, and exposure of the active sites of DLFCs. Selected recent studies on the use of foam in electrolyzers are also presented.