Hydrophilic/Aerophobic Hydrogen-Evolving Electrode: NiRu-Based Metal-Organic Framework Nanosheets In Situ Grown on Conductive Substrates

Direct Current Pulse Atmospheric Pressure Plasma Jet Treatment on Electrochemically Deposited NiFe/Carbon Paper and Its Potential Application in an Anion-Exchange Membrane Water Electrolyzer

An atmospheric pressure plasma jet (APPJ) is used to process electrochemically deposited NiFe on carbon paper (NiFe/CP). The reactive oxygen and nitrogen species (RONs) of the APPJ modify the surface properties, chemical bonding types, and oxidation states of the material at the self-sustained temperature of the APPJ. The APPJ treatment further enhances the hydrophilicity and creates a higher disorder level in the carbon material. Moreover, the metal carbide bonds of NiFe/CP formed in the electrochemical deposition (ED) process are converted to metal oxide bonds after APPJ processing. The potential application of APPJ treatment on NiFe/CP in alkaline water electrolysis is demonstrated. With more oxygen-containing species and better hydrophilicity after APPJ treatment, APPJ-treated NiFe/CP is applied as the electrocatalyst for the oxygen evolution reaction (OER) in alkaline water electrolysis. APPJ-treated NiFe/CP is also used in a custom-made anion-exchange membrane water electrolyzer (AEMWE); this should contribute toward realizing the practical large-scale application of AEM for hydrogen production.

Advancing H2O2 electrosynthesis: enhancing electrochemical systems, unveiling emerging applications, and seizing opportunities

Hydrogen peroxide (H2O2) is a highly desired chemical with a wide range of applications. Recent advancements in H2O2 synthesis center on the electrochemical reduction of oxygen, an environmentally friendly approach that facilitates on-site production. To successfully implement practical-scale, highly efficient electrosynthesis of H2O2, it is critical to meticulously explore both the design of catalytic materials and the engineering of other components of the electrochemical system, as they hold equal importance in this process. Development of promising electrocatalysts with outstanding selectivity and activity is a prerequisite for efficient H2O2 electrosynthesis, while well-configured electrolyzers determine the practical implementation of large-scale H2O2 production. In this review, we systematically summarize fundamental mechanisms and recent achievements in H2O2 electrosynthesis, including electrocatalyst design, electrode optimization, electrolyte engineering, reactor exploration, potential applications, and integrated systems, with an emphasis on active site identification and microenvironment regulation. This review also proposes new insights into the existing challenges and opportunities within this rapidly evolving field, together with perspectives on future development of H2O2 electrosynthesis and its industrial-scale applications.

Catalysis with Two-Dimensional Metal-Organic Frameworks: Synthesis, Characterization, and Modulation

The demand for the exploration of highly active and durable electro/photocatalysts for renewable energy conversion has experienced a significant surge in recent years. Metal-organic frameworks (MOFs), by virtue of their high porosity, large surface area, and modifiable metal centers and ligands, have gained tremendous attention and demonstrated promising prospects in electro/photocatalytic energy conversion. However, the small pore sizes and limited active sites of 3D bulk MOFs hinder their wide applications. Developing 2D MOFs with tailored thickness and large aspect ratio has emerged as an effective approach to meet these challenges, offering a high density of exposed active sites, better mechanical stability, better assembly flexibility, and shorter charge and photoexcited state transfer distances compared to 3D bulk MOFs. In this review, synthesis methods for the most up-to-date 2D MOFs are first overviewed, highlighting their respective advantages and disadvantages. Subsequently, a systematic analysis is conducted on the identification and electronic structure modulation of catalytic active sites in 2D MOFs and their applications in renewable energy conversion, including electrocatalysis and photocatalysis (electro/photocatalysis). Lastly, the current challenges and future development of 2D MOFs toward highly efficient and practical electro/photocatalysis are proposed.

Direct Seawater Electrolysis: From Catalyst Design to Device Applications

Direct seawater electrolysis (DSE) for hydrogen production, using earth-abundant seawater as the feedstock and renewable electricity as the driving source, paves a new opportunity for flexible energy conversion/storage and smooths the volatility of renewable energy. Unfortunately, the complex environments of seawater impose significant challenges on the design of DSE catalysts, and the practical performance of many current DSE catalysts remains unsatisfactory on the device level. However, many studies predominantly concentrate on the development of electrocatalysts for DSE without giving due consideration to the specific devices. To mitigate this gap, the most recent progress (mainly published within the year 2020-2023) of DSE electrocatalysts and devices are systematically evaluated. By discussing key bottlenecks, corresponding mitigation strategies, and various device designs and applications, the tremendous challenges in addressing the trade-off among activity, stability, and selectivity for DSE electrocatalysts by a single shot are emphasized. In addition, the rational design of the DSE electrocatalysts needs to align with the specific device configuration, which is more effective than attempting to comprehensively enhance all catalytic parameters. This work, featuring the first review of this kind to consider rational catalyst design in the framework of DSE devices, will facilitate practical DSE development.

"Bubble-Diode" Breathable Electrodes for Fast Gas Transport

Bubbles arising from wild gas evolution commonly exist in electrochemical systems, particularly in water electrolysis and rechargeable aqueous batteries (e. g., Zn-air batteries). Substantial energy dissipation occurs due to the obstruction of active sites and ion-conducting pathways by evolving bubbles. Efforts are made to elucidate effective strategies for fast gas transport, most of which focus on minimizing bubble size and facilitating their timely detachment through complex techniques such as constructing super-hydrophilic nano-structure electrodes, flowing electrolytes, and ultrasonic oscillation. Recently, an innovative, facile, and highly efficient method utilizing a breathable electrode design to promote gaseous molecules to the external environment emerges as a promising approach since it avoids remarkable bubble accumulation while remaining free of additional accessories. This paper highlights the origin and evolution of this promising design. Starting with introducing the basic concept of traditional breathable electrodes based on hydrophobic polymer networks and discussing the current progress made in underlying mechanisms, a detailed description of the advanced design inspired by a "bubble-diode" concept with superior breathability follows. This Concept aims to contribute to a deep understanding of this technology and paves the way for further advancements in this renewable energy era.

Improving oxygen reduction reaction by cobalt iron-layered double hydroxide layer on nickel-metal organic framework as cathode catalyst in microbial fuel cell

Cobalt Iron -layered double hydroxide (CoFe-LDH) nano sheets were attached to Nickel-metal organic frameworks (Ni-MOF) by utilizing hydrothermal reaction method, and CoFe-LDH@Ni-MOF was synthesized and worked as the cathode catalyst in microbial fuel cell. The surface of this composite material provided generous electrochemical active sites, consisting of wrinkled strips of CoFe-LDH adhering to a lamellar structure of Ni-MOF. In terms of the maximum output power density, CoFe-LDH@Ni-MOF as the catalyst was 211 mW/m2, 2.54 times higher than that of Ni-MOF (83 mW/m2), and it was stable at about 225 mV for 150 h. CoFe-LDH@Ni-MOF showed high oxygen reduction reaction capability and high specific surface area, and the electron transfer rate was accelerated. This work might set the stage for the development and utilization of fuel cell cathode catalysts.

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.

2D Metal-Organic Frameworks as Competent Electrocatalysts for Water Splitting

Hydrogen, a clean and flexible energy carrier, can be efficiently produced by electrocatalytic water splitting. To accelerate the sluggish hydrogen evolution reaction and oxygen evolution reaction kinetics in the splitting process, highly active electrocatalysts are essential for lowering the energy barriers, thereby improving the efficiency of overall water splitting. Combining the distinctive advantages of metal-organic frameworks (MOFs) with the physicochemical properties of 2D materials such as large surface area, tunable structure, accessible active sites, and enhanced conductivity, 2D MOFs have attracted intensive attention in the field of electrocatalysis. Different strategies, such as improving the conductivities of MOFs, reducing the thicknesses of MOF nanosheets, and integrating MOFs with conductive particles or substrates, are developed to promote the catalytic performances of pristine MOFs. This review summarizes the recent advances of pristine 2D MOF-based electrocatalysts for water electrolysis. In particular, their intrinsic electrocatalytic properties are detailly analyzed to reveal important roles of inherent MOF active centers, or other in situ generated active phases from MOFs responsible for the catalytic reactions. Finally, the challenges and development prospects of pristine 2D MOFs for the future applications in overall water splitting are discussed.

CeO2/Ni-MOF with Synergistic Function of Enrichment and Activation: Efficient Reduction of 4-Nitrophenol Pollutant to 4-Aminophenol

The conversion of organic pollutants to value-added chemicals has been considered as a sustainable approach to solve environmental problems. However, it is still a challenge to construct a suitable heterogeneous catalyst that can synchronously achieve the enrichment and activation of organic pollutants (such as 4-nitrophenol, 4-NP). Here, an organic-inorganic hybrid catalyst (CeO₂/Ni-MOF) was successfully fabricated for efficiently reducing 4-NP to 4-aminophenol (4-AP) with water as the hydrogen source. Based on the synergistic effect of Ni-MOF (adsorption action) and CeO₂ (active sites), CeO₂/Ni-MOF could achieve a reaction rate of 1.102 μmol min^-1 mg^-1 with an ultrahigh Faraday efficiency (FE) (99.9%) and conversion (97.6%). In addition, the catalytic mechanism of 4-NP reduction over CeO₂/Ni-MOF was elaborated in depth. This work presents a new avenue for the effective reduction of pollutants and provides a new strategy for designing high-performance catalysts for rare-earth metals.

Metal-Organic Frameworks and Their Composites for Environmental Applications

From the point of view of the ecological environment, contaminants such as heavy metal ions or toxic gases have caused harmful impacts on the environment and human health, and overcoming these adverse effects remains a serious and important task. Very recent, highly crystalline porous metal-organic frameworks (MOFs), with tailorable chemistry and excellent chemical stability, have shown promising properties in the field of removing various hazardous pollutants. This review concentrates on the recent progress of MOFs and MOF-based materials and their exploit in environmental applications, mainly including water treatment and gas storage and separation. Finally, challenges and trends of MOFs and MOF-based materials for future developments are discussed and explored.

Recent Progress of Advanced Conductive Metal-Organic Frameworks: Precise Synthesis, Electrochemical Energy Storage Applications, and Future Challenges

Metal-organic frameworks (MOFs) with diverse composition, tunable structure, and unique physicochemical properties have emerged as promising materials in various fields. The tunable pore structure, abundant active sites, and ultrahigh specific surface area can facilitate mass transport and provide outstanding capacity, making MOFs an ideal active material for electrochemical energy storage and conversion. However, the poor electrical conductivity of pristine MOFs severely limits their applications in electrochemistry. Developing conductive MOFs has proved to be an effective solution to this problem. This review focuses on the design and synthesis of conductive MOF composites with judiciously chosen conducting materials, pristine MOFs, and assembly methods, as well as the preparation of intrinsically conductive MOFs based on building 2D π-conjugated structures, introducing mixed-valence metal ions/redox-active ligands, designing π-π stacked pathways, and constructing infinite metal-sulfur chains (-M-S-)_∞ . Furthermore, recent progress and challenges of conductive MOFs for energy storage and conversion (supercapacitors, Li-ion batteries, Li-S batteries, and electrochemical water splitting) are summarized.

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.

Electrocatalyst Design for Conversion of Energy Molecules: Electronic State Modulation and Mass Transport Regulation

Electrocatalytic conversions of energy molecules are involved in many energy conversion processes. Improving the activity of electrocatalyst is critical for increasing the efficiency of these energy conversion processes. However, the...

Ir-doped Co(OH)2 Nanosheets as Efficient Electrocatalyst for Oxygen Evolution Reaction

In recent years, Co-based metal-organic frameworks (Co-MOFs) have received significant research interest because of their large specific surface area, high porosity, tunable structure and topological flexibility. However, the comparatively weak...

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.

Ni3S2/Ni Heterostructure Nanobelt Arrays as Bifunctional Catalysts for Urea-Rich Wastewater Degradation

Urea electrolysis is a cost-effective method for urea-rich wastewater degradation to achieve a pollution-free environment. In this work, the Ni₃S₂/Ni heterostructure nanobelt arrays supported on nickel foam (Ni₃S₂/Ni/NF) are synthesized for accelerating the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). It only needs ultralow potentials of 1.30 V and -54 mV to achieve the current density of ±10 mA cm^-2 for UOR and HER, respectively. Meanwhile, the overall urea oxidation driven by Ni₃S₂/Ni/NF only needs 1.36 V to achieve 10 mA cm^-2, and it can remain at 100 mA cm^-2 for 60 h without obvious activity attenuation. The superior performance could be attributed to the heterostructure between Ni₃S₂ and Ni, which can promote electron transfer and form electron-poor Ni species to optimize urea decomposition and hydrogen production. Moreover, the nanobelt self-supported structure could expose abundant active sites. This work thus provides a feasible and cost-effective strategy for urea-rich wastewater degradation and hydrogen production.

Mesoporous RhRu Nanosponges with Enhanced Water Dissociation toward Efficient Alkaline Hydrogen Evolution

Lowering the energy barrier of water dissociation is critical to achieving highly efficient hydrogen evolution in alkaline conditions. Herein, we reported mesoporous RhRu nanosponges with enhanced water dissociation behavior as a new class of high-performance electrocatalysts for alkaline hydrogen evolution reaction (HER). The obtained nanosponges have a binary alloy structure (fcc) and a highly porous structure with high surface area. Our RhRu catalyst displayed an outstanding HER activity with an overpotential of 25 mV at 10 mA cm^-2 and a Tafel slope of 47.5 mV dec^-1 in 1.0 M KOH, which significantly outperformed that of commercial Pt/C catalyst and was even comparable to the classic Pt/metal (hydro)oxide catalysts. Density functional theory (DFT) calculations disclosed that charge redistribution on the RhRu alloy surface enabled tuning of the Ru d-band center and then promoted the adsorption and dissociation of water molecules. Based on the experimental results and theoretical modeling, a bifunctional mechanism contributed to the remarkable alkaline HER activity on the RhRu catalyst surface.