Low-Cost Self-Reconstructed High Entropy Oxide as an Ultra-Durable OER Electrocatalyst for Anion Exchange Membrane Water Electrolyzer.

Future energy loss can be minimized to a greater extent via developing highly active electrocatalysts for alkaline water electrolyzers. Incorporating an innovative design like high entropy oxides, dealloying, structural reconstruction, in situ activation can potentially reduce the energy barriers between practical and theoretical potentials. Here, a Fd-3m spinel group high entropy oxide is developed via a simple solvothermal and calcination approach. The developed (FeCoMnZnMg)3O4 electrocatalyst shows a near equimolar distribution of all the metal elements resulting in higher entropy (ΔS ≈1.61R) and higher surface area. The self-reconstructed spinel high entropy oxide (S-HEO) catalyst exhibited a lower overpotential of 240 mV to reach 10 mA cm-2 and enhanced reaction kinetics (59 mV dec-1). Noticeably, the S-HEO displayed an outstanding durability of 1000 h without any potential loss, significantly outperforming most of the reported OER electrocatalysts. Further, S-HEO is evaluated as the anode catalyst for an anion exchange membrane water electrolyzer (AEMWE) in 1 m, 0.1 m KOH, and DI water at 20 and 60 °C. These results demonstrate that S-HEO is a highly attractive, non-noble class of materials for high active oxygen evolution reaction (OER) electrocatalysts allowing fine-tuning beyond the limits of bi- or trimetallic oxides.

Phase Electronic Structure Tuning via Pt, P-Doped Ni4Mo-Implanted Ti4O7 for Highly Efficient Water Splitting and Mg/Seawater Batteries.

Fine-tuning nanoscale structures, morphologies, and electronic states are crucial for creating efficient water-splitting electrocatalysts. In this study, a method for electronic structure engineering to enhance overall water splitting in a corrosion-resistant electrocatalyst matrix by integrating Pt, P dual-doped Ni4Mo electrocatalysts onto a Ti4O7 nanorod grown on carbon cloth (Pt, P-Ni4Mo-Ti4O7/CC) is introduced. By optimizing platinum and phosphorus concentrations to 1.18% and 2.42%, respectively, low overpotentials are achieved remarkably: 24 mV at 10 mA cm-2 for the hydrogen evolution reaction and 290 mV at 20 mA cm-2 for the oxygen evolution reaction in 1.0 m KOH. These values approach or surpass those of benchmark Pt-C and IrO2 catalysts. Additionally, the Pt, P-Ni4Mo-Ti4O7/CC bifunctional electrocatalyst displays low cell potentials across various mediums, maintaining excellent current retention (96% stability after 40 h in mimic seawater at 20 mA cm-2) and demonstrating strong corrosion resistance and suitability for seawater  electrolysis. As a cathode in magnesium/seawater batteries, it achieves a power density of 7.2 mW cm-2 and maintains stability for 100 h. Density functional theory simulations confirm that P, Pt doping-assisted electronic structure modifications augment electrical conductivity and active sites in the hybrid electrocatalysts.

Low-Cost Hydrogen Production from Alkaline/Seawater over a Single-Step Synthesis of Mo3 Se4 -NiSe Core-Shell Nanowire Arrays.

The rational design and steering of earth-abundant, efficient, and stable electrocatalysts for hydrogen generation is highly desirable but challenging with catalysts free of platinum group metals (PGMs). Mass production of high-purity hydrogen fuel from seawater electrolysis presents a transformative technology for sustainable alternatives. Here, a heterostructure of molybdenum selenide-nickel selenide (Mo3 Se4 -NiSe) core-shell nanowire arrays constructed on nickel foam by a single-step in situ hydrothermal process is reported. This tiered structure provides improved intrinsic activity and high electrical conductivity for efficient charge transfer and endows excellent hydrogen evolution reaction (HER) activity in alkaline and natural seawater conditions. The Mo3 Se4 -NiSe freestanding electrodes require small overpotentials of 84.4 and 166 mV to reach a current density of 10 mA cm-2 in alkaline and natural seawater electrolytes, respectively. It maintains an impressive balance between electrocatalytic activity and stability. Experimental and theoretical calculations reveal that the Mo3 Se4 -NiSe interface provides abundant active sites for the HER process, which modulate the binding energies of adsorbed species and decrease the energetic barrier, providing a new route to design state-of-the-art, PGM-free catalysts for hydrogen production from alkaline and seawater electrolysis.

Trimetallic Oxide Electrocatalyst for Enhanced Redox Activity in Zinc-Air Batteries Evaluated by In Situ Analysis.

Researchers are investigating innovative composite materials for renewable energy and energy storage systems. The major goals of this studies are i) to develop a low-cost and stable trimetallic oxide catalyst and ii) to change the electrical environment of the active sites through site-selective Mo substitution. The effect of Mo on NiCoMoO4 is elucidated using both in situ X-ray absorption spectroscopy and X-ray diffraction analysis. Also, density functional theory strategies show that NiCoMoO4 has extraordinary catalytic redox activity because of the high adsorption energy of the Mo atom on the active crystal plane. Further, it is demonstrated that hierarchical nanoflower structures of NiCoMoO4 on reduced graphene oxide can be employed as a powerful bifunctional electrocatalyst for oxygen reduction/evolution reactions in alkaline solutions, providing a small overpotential difference of 0.75 V. Also, Zn-air batteries based on the developed bifunctional electrocatalyst exhibit outstanding cycling stability and a high-power density of 125.1 mW cm-2 . This work encourages the use of Zn-air batteries in practical applications and provides an interesting concept for designing a bifunctional electrocatalyst.

Developing Outstanding Bifunctional Electrocatalysts for Rechargeable Zn-Air Batteries Using High-Purity Spinel-Type ZnCo2 Se4 Nanoparticles.

Zinc-air batteries are gaining popularity as viable energy sources for green energy storage technologies. The cost and performance of Zn-air batteries are mostly determined by the air electrodes in combination with an oxygen electrocatalyst. This research aims at the particular innovations and challenges relating to air electrodes and related materials. Here, a nanocomposite of ZnCo2 Se4 @rGO that exhibits excellent electrocatalytic activity for the oxygen reduction reaction, ORR (E1/2  = 0.802 V), and oxygen evolution reaction, OER (η10  = 298 mV@10 mA cm-2 ) is synthesized. In addition, a rechargeable zinc-air battery with ZnCo2 Se4 @rGO as the cathode showed a high open circuit voltage (OCV) of 1.38 V, a peak power density of 210.4 mW cm-2 , and outstanding long-term cycling stability. The electronic structure and oxygen reduction/evolution reaction mechanism of the catalysts ZnCo2 Se4 and Co3 Se4 are further investigated using density functional theory calculations. Finally, a perspective for designing, preparing, and assembling air electrodes is suggested for the future developments of high-performance Zn-air batteries.

Highly Effective Freshwater and Seawater Electrolysis Enabled by Atomic Rh-Modulated Co-CoO Lateral Heterostructures.

Atomic metal-modulated heterostructures have been evidenced as an exciting solution to develop high-performance multifunctional electrocatalyst toward water splitting. In this research, a catalyst of continuous cobalt-cobalt oxide (Co-CoO) lateral heterostructures implanted with well-dispersed rhodium (Rh) atoms and shelled over conductive porous 1D copper (Cu) nano-supports for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in both freshwater and seawater under alkaline condition is proposed. It is found that synergistic effects coming from uniform Rh atoms at doping level and Co-CoO heterostructures afford rich multi-integrated active sites and excellent charge transfer, thereby effectively promoting both HER and OER activities. The material requires overpotentials of 107.3 and 137.7 mV for HER and 277.7 and 260 mV for OER to reach an output of 10 mA cm-1 in freshwater and mimic seawater, respectively, surpassing earlier reported catalysts. Compared to a benchmark a Pt/C//RuO2 -based two-electrode electrolyzer, a device derived from the 1D-Cu@Co-CoO/Rh on copper foam delivers comparable cell voltages of 1.62, 1.60, and 1.70 V at 10 mA cm-2 in freshwater, mimic seawater, and natural seawater, respectively, together with robust stability. These results evidence that 1D-Cu@Co-CoO/Rh is a promising catalyst for green hydrogen generation via freshwater and seawater electrolysis applications.

Bifunctional Catalyst Derived from Sulfur-Doped VMoOx Nanolayer Shelled Co Nanosheets for Efficient Water Splitting.

A novel sulfur-doped vanadium-molybdenum oxide nanolayer shelling over two-dimensional cobalt nanosheets (2D Co@S-VMoOx NSs) was synthesized via a facile approach. The formation of such a unique 2D core@shell structure together with unusual sulfur doping effect increased the electrochemically active surface area and provided excellent electric conductivity, thereby boosting the activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As a result, only low overpotentials of 73 and 274 mV were required to achieve a current response of 10 mA cm-2 toward HER and OER, respectively. Using the 2D Co@S-VMoOx NSs on nickel foam as both cathode and anode electrode, the fabricated electrolyzer showed superior performance with a small cell voltage of 1.55 V at 10 mA cm-2 and excellent stability. These results suggested that the 2D Co@S-VMoOx NSs material might be a potential bifunctional catalyst for green hydrogen production via electrochemical water splitting.

Hierarchical 3D Oxygenated Cobalt Molybdenum Selenide Nanosheets as Robust Trifunctional Catalyst for Water Splitting and Zinc-Air Batteries.

The development of hierarchical nanostructures with highly active and durable multifunctional catalysts has a new significance in the context of new energy technologies of water splitting and metal-air batteries. Herein, a strategy is demonstrated to construct a 3D hierarchical oxygenated cobalt molybdenum selenide (O-Co1- x Mox Se2 ) series with attractive nanoarchitectures, which are fabricated by a simple and cost-effective hydrothermal process followed by an exclusive ion-exchange process. Owing to its highly electroactive sites with numerous nanoporous networks and plentiful oxygen vacancies, the optimal O-Co0.5 Mo0.5 Se2 could catalyze the hydrogen evolution reaction and oxygen evolution reaction effectively with a low overpotential of ≈102 and 189 mV, at a current density of 10 mA cm-2 , respectively, and exceptional durability. Most importantly, the O-Co0.5 Mo0.5 Se2 ||O-Co0.5 Mo0.5 Se2 water splitting device only entails a voltage of ≈1.53 V at a current density of 10 mA cm-2 , which is much better than benchmark Pt/C||RuO2 (≈1.56 V). Furthermore, O-Co0.5 Mo0.5 Se2 air cathode-based zinc-air batteries exhibit an excellent power density of 120.28 mW cm-2 and exceptional cycling stability for 60 h, superior to those of state-of-art Pt/C+RuO2 pair-based zinc-air batteries. The present study provides a strategy to design hierarchical 3D oxygenated bimetallic selenide-based multifunctional catalysts for energy conversion and storage systems.