Boosting the OER Performance of Nitrogen-Doped Ni Nanoclusters Confined in an Amorphous Carbon Matrix

Electron-deficient Co7Fe3 induced by interfacial effect of molybdenum carbide boosting oxygen evolution reaction

Developing a high-activity and low-cost catalyst to reduce the anodic overpotential is essential for hydrogen production from water splitting. In this work, a hetero-structured Co7Fe3/Mo2C@C catalyst has been developed to efficiently catalyze oxygen evolution reaction (OER), the overpotential (ƞ10) of Co7Fe3/Mo2C@C-catalyzed OER with current density of 10 mA/cm2 is about 254 mV, substantially lower than the counterparts of Co7Fe3@C-catalyzed OER (ƞ10, 308 mV) and Mo2C@C-catalyzed OER (ƞ10, 439 mV), close to that of OER catalyzed by commercial RuO2. The mechanistic studies reveal that the distinct electron transfer across the Co7Fe3/Mo2C interface results in electron-deficient Co7Fe3, which has been identified as the highly active catalytic sites. Density functional theory (DFT) calculations manifest that Mo2C induces a distinct decrease in electron density on Co7Fe3 and upgrades the d-band centers of Co and Fe in Co7Fe3 towards Fermi energy level, thus substantially lowering the energy barrier of the rate-determining reaction step and conferring significantly improved OER activity on the Co7Fe3/Mo2C@C catalyst.

Conductive Gels for Energy Storage, Conversion, and Generation: Materials Design Strategies, Properties, and Applications

Gel-based materials have garnered significant interest in recent years, primarily due to their remarkable structural flexibility, ease of modulation, and cost-effective synthesis methodologies. Specifically, polymer-based conductive gels, characterized by their unique conjugated structures incorporating both localized sigma and pi bonds, have emerged as materials of choice for a wide range of applications. These gels demonstrate an exceptional integration of solid and liquid phases within a three-dimensional matrix, further enhanced by the incorporation of conductive nanofillers. This unique composition endows them with a versatility that finds application across a diverse array of fields, including wearable energy devices, health monitoring systems, robotics, and devices designed for interactive human-body integration. The multifunctional nature of gel materials is evidenced by their inherent stretchability, self-healing capabilities, and conductivity (both ionic and electrical), alongside their multidimensional properties. However, the integration of these multidimensional properties into a single gel material, tailored to meet specific mechanical and chemical requirements across various applications, presents a significant challenge. This review aims to shed light on the current advancements in gel materials, with a particular focus on their application in various devices. Additionally, it critically assesses the limitations inherent in current material design strategies and proposes potential avenues for future research, particularly in the realm of conductive gels for energy applications.

Branched Porous Ni3N as a Catalytic Electrode for Selective Semidehydrogenation of Tetrahydroisoquinoline

Oxygen evolution in electrochemical water splitting needs a high overpotential that significantly reduces the energy efficiency. To explore an alternative anodic reaction to promote the production of hydrogen at the other end of water splitting and at the same time to get high-value-added chemicals is highly desirable. Herein, we demonstrate a novel branched porous Ni3N catalyst that is prepared for dehydrogenation of tetrahydroisoquinoline, which acts as an anodic oxidation reaction to promote H2 formation on the other end. Interestingly, the Ni3N catalytic electrode can induce effective semidehydrogenation with the selective formation of dihydroisoquinoline, which is difficult to be obtained by the usual direct synthesis route. The catalytic electrode exhibits a low potential of 1.55 V (vs RHE) for a catalytic current density of 61 mA cm-2 with dehydrogenation of tetrahydroisoquinoline and hydrogen production. In situ Raman spectra studies suggest that NiOOH is formed on the electrode surface, which mediates the oxidation semidehydrogenation process. This work also provides a strategy to fabricate nitride materials for applications beyond selective semidehydrogenation of tetrahydroisoquinoline.

Confinement Accelerates Water Oxidation Catalysis: Evidence from In Situ Studies

Basic insight into the structural evolution of electrocatalysts under operating conditions is of substantial importance for designing water oxidation catalysts. The first-row transition metal-based catalysts present state-of-the-art oxygen evolution reaction (OER) performance under alkaline conditions. Apparently, confinement has become an exciting strategy to boost the performance of these catalysts. The van der Waals (vdW) gaps of transition metal dichalcogenides are acknowledged to serve as a suitable platform to confine the first-row transition metal catalysts. This study focuses on confining Ni(OH)2 nanoparticle in the vdW gaps of 2D exfoliated SnS2 (Ex-SnS2 ) to accelerate water oxidation and to guarantee long term durability in alkaline solutions. The trends in oxidation states of Ni are probed during OER catalysis. The in situ studies confirm that the confined system produces a favorable environment for accelerated oxygen gas evolution, whereas the un-confined system proceeds with a relatively slower kinetics. The outstanding OER activity and excellent stability, with an overpotential of 300 mV at 100 mA cm-2 and Tafel slope as low as 93 mV dec-1 results from the confinement effect. This study sheds light on the OER mechanism of confined catalysis and opens up a way to develop efficient and low-cost electrocatalysts.

Synergistic Coupling of Charge Extraction and Sinking in Cu5FeS4/Ni3S2@NF for Photoassisted Electrocatalytic Oxygen Evolution

Exploring low-cost and high-performance oxygen evolution reaction (OER) catalysts has attracted great attention due to their crucial role in water splitting. Here, a bifunctional Cu5FeS4/Ni3S2@NF catalyst was in situ formed on a nickel (Ni) foam toward efficient photoassisted electrocatalytic (P-EC) OER, which displays an ultralow overpotential of 260 mV at 30 mA cm-2 in alkaline solution, outperforming most previously reported Ni-based catalysts. It also shows great potential in degradation of antibiotics as an alternative anode reaction to OER owing to the prompt transfer of photogenerated holes. The photocurrent test and transient photovoltage spectroscopy indicate that the synergistic coupling of charge extraction and sinking effects in Cu5FeS4 and Ni3S2 is critical for boosting the OER activity via photoassistance. Electrochemical active surface area and electrochemical impedance spectroscopy tests further prove that the photogenerated electromotive force can effectively compensate the overpotential of OER. This work not only provides a good guidance for integrating photocatalysis and electrocatalysis, but also indicates the key role of synergistic extraction and utilization of photogenerated charge carriers in P-EC.

Improved Alkaline Seawater Splitting of NiS Nanosheets by Iron Doping

Seawater electrolysis driven by renewable electricity is deemed a promising and sustainable strategy for green hydrogen production, but it is still formidably challenging. Here, we report an iron-doped NiS nanosheet array on Ni foam (Fe-NiS/NF) as a high-performance and stable seawater splitting electrocatalyst. Such Fe-NiS/NF catalyst needs overpotentials of only 420 and 270 mV at 1000 mA cm^-2 for the oxygen evolution reaction and hydrogen evolution reaction in alkaline seawater, respectively. Furthermore, its two-electrode electrolyzer needs a cell voltage of 1.88 V for 1000 mA cm^-2 with 50 h of long-term electrochemical durability in alkaline seawater. Additionally, in situ electrochemical Raman and infrared spectroscopy were employed to detect the reconstitution process of NiOOH and the generation of oxygen intermediates under reaction conditions.

Suppressing the Surface Amorphization of Ba0.5Sr0.5Co0.8Fe0.2O3-δ Perovskite toward Oxygen Catalytic Reactions by Introducing the Compressive Stress

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) perovskite has been recognized as a promising oxygen evolution reaction (OER) catalyst due to its superior intrinsic catalytic activity. However, BSCF suffers from serious degradation during the OER process due to its surface amorphization caused by the segregation of A-site ions (Ba²⁺ and Sr²⁺). Herein, we construct a novel BSCF composite catalyst (BSCF-GDC-NR) by anchoring the gadolinium-doped ceria oxide (GDC) nanoparticles on the surface of a BSCF nanorod by a concentration-difference electrospinning method. Our BSCF-GDC-NR has greatly improved bifunctional oxygen catalytic activity and stability toward both oxygen reduction reaction (ORR) and OER compared with the pristine BSCF. The improvement of the stability can be related to that anchoring GDC on BSCF effectively suppresses the segregation and dissolution of A-site elements in BSCF during the preparation and catalytic processes. The suppression effects are ascribed to the introduction of compressive stress between BSCF and GDC, which greatly inhibits the diffusions of Ba and Sr ions. This work can give a guidance for developing the perovskite oxygen catalysts with high activity and stability.

Ce-Modified Flowerlike NiFe-MOF Nanostructure Based on Ion Competitive Coordination for Enhancing the Oxygen Evolution Reaction

Metal-organic framework (MOF) has become a popular electrocatalyst for the oxygen evolution reaction (OER) because of its large specific surface area and adjustable porosity. Nevertheless, the electrochemical performance of MOFs has been greatly limited by poor intrinsic conductivity and catalytic activity. Herein, we report a Ce-doped nanoflower-like MOF material Ce@NiFe-MOF-5 via a facile ion competitive coordination effect and doping method. Benefiting from the nanoflower structure formed by the stacking of nanosheets, a large number of active sites can be exposed, which favors electron/mass transfer during water oxidation. The coordination substitution of Ce ions not only promoted an increase in the number of active sites on the surface of the nanosheets but also optimized the electronic structure of pristine NiFe-MOF. The well-designed Ce@NiFe-MOF-5 catalysts exhibited superior OER performance under basic conditions, which only required an overpotential of 258 mV at a current density of 10 mA cm^-2 and a Tafel slope of 54.44 mV dec^-1. Moreover, when Ce@NiFe-MOF-5 served as an anode and Pt/C as a cathode, the two-electrode system only needed 1.56 V to drive overall water splitting at 10 mA cm^-2.

Ni-O4 as Active Sites for Efficient Oxygen Evolution Reaction with Electronic Metal-Support Interactions

Precise adjustment of the metal site structure in single-atom catalysts (SACs) plays a key role in addressing the oxygen evolution reaction (OER). Herein, we report the synthesis of O-doped Ni SACs anchored on porous graphene-like carbon (Ni-O-G) using molten salts (ZnCl₂ and NaCl) as templates, in which the unique Ni-O₄ structure serves as the active sites. Ni-O-G, with an overpotential of only 238 mV (@ 10 mA cm^-2), is one of the more advanced catalysts. An array of characterizations and density functional theory calculations show that the Ni-O₄ coordination enables Ni to be closer to the Fermi level compared to traditional Ni-N₄, enhancing the electronic metal-support interaction to facilitate OER kinetics. Thus, this work offers an alternative strategy for the structural modulation of Ni SACs and the effect of different coordination elements with the same atomic coordination structure on the intrinsic OER activity.

Iron-modulated Ni3S2 derived from a Ni-MOF-based Prussian blue analogue for a highly efficient oxygen evolution reaction

Developing efficient, environmentally friendly and cost-effective non-precious metal electrocatalysts for the oxygen evolution reaction (OER) is essential to alleviate the energy crisis and environmental pollution.