Structure-Performance Correlation Inspired Platinum-Assisted Anode with a Homogeneous Ionomer Layer for Proton Exchange Membrane Water Electrolysis

PEMWE is becoming one of the most promising technologies for efficient and green hydrogen production, while the anode OER process is deeply restricted by the now commercially used iridium oxide with sluggish reaction kinetics and super high cost. Deeply exploring the essential relationship between the underlying substrate materials and the performance of PEMWE cells while simultaneously excavating new practical and convenient methods to reduce costs and increase efficiency is full of challenges. Herein, two representative kinds of iridium oxide were studied, and their performance difference in PEMWE was precisely analyzed with electrochemical techniques and physical characterization and further linked to the ionomer/catalyst compound features. A novel anode with a uniform thin ionomer coating was successfully constructed, which simultaneously optimized the ionomer/catalyst aggregates as well as electrical conductivity, resulting in significantly enhanced PEMWE performance. This rigorous qualitative analysis of the structure-performance relationship as well as effective ionomer-affinitive optimization strategies are of great significance to the development of next-generation high-performance PEM water electrolyzers.

Metal ferrites-based nanocomposites and nanohybrids for photocatalytic water treatment and electrocatalytic water splitting

Photocatalytic degradation is one of the most promising technologies available for removing a variety of synthetic and organic pollutants from the environmental matrices because of its high catalytic activity, reduced energy consumption, and low total cost. Due to its acceptable bandgap, broad light-harvesting efficiency, significant renewability, and stability, Fe₂O₃ has emerged as a fascinating material for the degradation of organic contaminants as well as numerous dyes. This study thoroughly reviewed the efficiency of Fe₂O₃-based nanocomposite and nanomaterials for water remediation. Iron oxide structure and various synthetic methods are briefly discussed. Additionally, the electrocatalytic application of Fe₂O₃-based nanocomposites, including oxygen evolution reaction, oxygen reduction reaction, hydrogen evolution reaction, and overall water splitting efficiency, was also highlighted to illustrate the great promise of these composites. Finally, the ongoing issues and future prospects are directed to fully reveal the standards of Fe₂O₃-based catalysts. This review is intended to disseminate knowledge for further research on the possible applications of Fe₂O₃ as a photocatalyst and electrocatalyst.

Part II: NiMoO4 Nanostructures Synthesized by the Solution Combustion Method: A Parametric Study on the Influence of Material Synthesis and Electrode-Fabrication Parameters on the Electrocatalytic Activity in the Hydrogen Evolution Reaction

Earth-abundant NiMo-oxide nanostructures were investigated as efficient electrocatalytic materials for the hydrogen evolution reaction (HER) in acidic media. Synthesis and non-synthesis parameters were thoroughly studied. For the non-synthesis parameters, the variation in Nafion loading resulted in a volcano-like trend, while the change in the electrocatalyst loading showed that the marginal benefit of high loadings attenuates due to mass-transfer limitations. The addition of carbon black to the electrocatalyst layer improved the HER performance at low loadings. Different carbon black grades showed a varying influence on the HER performance. Regarding the synthesis parameters, a calcination temperature of 500 °C, a calcination time between 20 and 720 min, a stoichiometric composition (Ni/Mo = 1), an acidic precursor solution, and a fuel-lean system were conditions that yielded the highest HER activity. The in-house NiMoO4/CB/Nafion electrocatalyst layer was found to offer a better long-term performance than the commercial Pt/C.

Unravelling the Role of Strong Metal-Support Interactions in Boosting the Activity toward Hydrogen Evolution Reaction on Ir Nanoparticle/N-Doped Carbon Nanosheet Catalysts

Pt-based catalysts are commercial electrocatalysts for the hydrogen evolution reaction (HER), but their shortcomings of expensive and imperfect efficiency hinder their large-scale application. Here, we report an Ir-based HER catalyst supported by N-doped carbon nanosheets (Ir-NCNSs). The NCNSs, with a high surface area and unique atomic composition, enable Ir nanoparticles (NPs) to disperse at 2-3 nm and strongly coordinate to the Ir through Ir-N bonds, which exposes many active sites and strengthens their durability. The catalyst displays a low overpotential and a small Tafel slope of 46.3 mV at 10 mA cm^-2 and 52 mV dec^-1 in 0.5 M H₂SO₄, respectively. When used in 1.0 M KOH, Ir-NCNSs also show excellent electrocatalytic activity with a low overpotential of 125 mV at 10 mA cm^-2. The calculated results further suggest that Ir NPs and NCNSs have excellent selectivity for strong metal-support interactions, corresponding to a significant and stable HER characteristic. Our findings provide insight into the design of high-efficiency Ir-based HER catalysts.

Enhanced Oxygen Evolution Electrocatalysis in Strained A-Site Cation Deficient LaNiO3 Perovskite Thin Films

As the BO₆ octahedral structure in perovskite oxide is strongly linked with electronic behavior, it is actively studied for various fields such as metal-insulator transition, superconductivity, and so on. However, the research about the relationship between water-splitting activity and BO₆ structure is largely lacking. Here, we report the oxygen evolution reaction (OER) of LaNiO₃ (LNO) by changing the NiO₆ structure using compositional change and strain. The 5 atom % La deficiency in LNO resulted in an increase of the Ni-O-Ni bond angle and an expansion of bandwidth, enhancing the charge transfer ability. In-plane compressive strain derives the higher d_z² orbital occupancy, leading to suitable metal-oxygen bond strength for OER. Because of the synergistic effect of A-site deficiency and compressive strain, the overpotential (η) of compressively strained L_0.95NO film is reduced to 130 mV at j = 30 μA/cm² compared with nonstrained LNO (η = 280 mV), indicating a significant enhancement in OER.

Design-controlled synthesis of IrO2 sub-monolayers on Au nanoflowers: marrying plasmonic and electrocatalytic properties

We develop herein plasmonic-catalytic Au-IrO₂ nanostructures with a morphology optimized for efficient light harvesting and catalytic surface area; the nanoparticles have a nanoflower morphology, with closely spaced Au branches all partially covered by an ultrathin (1 nm) IrO₂ shell. This nanoparticle architecture optimizes optical features due to the interactions of closely spaced plasmonic branches forming electromagnetic hot spots, and the ultra-thin IrO₂ layer maximizes efficient use of this expensive catalyst. This concept was evaluated towards the enhancement of the electrocatalytic performances towards the oxygen evolution reaction (OER) as a model transformation. The OER can play a central role in meeting future energy demands but the performance of conventional electrocatalysts in this reaction is limited by the sluggish OER kinetics. We demonstrate an improvement of the OER performance for one of the most active OER catalysts, IrO₂, by harvesting plasmonic effects from visible light illumination in multimetallic nanoparticles. We find that the OER activity for the Au-IrO₂ nanoflowers can be improved under LSPR excitation, matching best properties reported in the literature. Our simulations and electrocatalytic data demonstrate that the enhancement in OER activities can be attributed to an electronic interaction between Au and IrO₂ and to the activation of Ir-O bonds by LSPR excited hot holes, leading to a change in the reaction mechanism (rate-determinant step) under visible light illumination.

Bimetallic Doped RuO2 with Manganese and Iron as Electrocatalysts for Favorable Oxygen Evolution Reaction Performance

Synthesizing oxygen evolution reaction (OER) catalysts with enhanced activity by codoping has been proven to be a feasible approach for the efficient use of noble metals via renewing their basic intrinsic properties. In continuation of the research in codoping, we prepare a ruthenium-based bimetallic doped catalyst Mn _x Fe _y Ru_1-x-y O₂ with an outstanding OER activity as compared to pure RuO₂, one of the state-of-the-art OER catalysts. The synthesized codoped RuO₂ with a Mn/Fe molar ratio of 1 reflected a Tafel slope of only 41 mV dec^-1, which is appreciably lower than 64 mV dec^-1 for pure RuO₂. The X-ray photoelectron spectroscopy (XPS) performed reveals that oxygen vacancy and manganese valency are the key factors of the OER activity for codoped catalysts.

Fabrication of γ-Fe2O3 Nanowires from Abundant and Low-cost Fe Plate for Highly Effective Electrocatalytic Water Splitting

Water splitting is thermodynamically uphill reaction, hence it cannot occur easily, and also highly complicated and challenging reaction in chemistry. In electrocatalytic water splitting, the combination of oxygen and hydrogen evolution reactions produces highly clean and sustainable hydrogen energy and which attracts research communities. Also, fabrication of highly active and low cost materials for water splitting is a major challenge. Therefore, in the present study, γ-Fe₂O₃ nanowires were fabricated from highly available and cost-effective iron plate without any chemical modifications/doping onto the surface of the working electrode with high current density. The fabricated nanowires achieved the current density of 10 mA/cm² at 1.88 V vs. RHE with the scan rate of 50 mV/sec. Stability measurements of the fabricated Fe₂O₃ nanowires were monitored up to 3275 sec with the current density of 9.6 mA/cm² at a constant potential of 1.7 V vs. RHE and scan rate of 50 mV/sec.

Transition metal mixed oxide-embedded graphene oxide bilayers as an efficient electrocatalyst for optimizing hydrogen evolution reaction in alkaline media

A novel electrocatalyst containing different percentages of iron-titanium mixed oxide onto graphene oxide (GO) support was prepared by embedding via the thermal decomposition method (TD) and was coated on a Cu substrate through facile electroless Ni–Co–P plating.