Non-Stoichiometry Induced Exsolution of Metal Oxide Nanoparticles via Formation of Wavy Surfaces and their Enhanced Electrocatalytic Activity: Case of Misfit Calcium Cobalt Oxide

Interplay of Size and Magnetic Effects in Electrocatalytic Water Oxidation Activity of Sub-10 nm NiOx Supported Porous Hard-Carbons

This report describes a systematic approach for precise engineering of a catalyst-metal oxide interface through combining complementary approaches of chemical vapor deposition and atomic layer deposition. Specifically, Chemical Vapor Deposition (CVD) fabricated nanostructured hard-carbon framework (NCF) is employed as synergistic support for precise deposition of NiOx particles through Atomic Layer Deposition (ALD). The three variants of NCF-NiOx system (dimensions ranging from 3-12 nm, surface coverage ranging from 0.14 %-2 %) achieved exhibit unique electrocatalytic water oxidation activities, that are further strongly influenced by an external magnetic field (Hext). This confluence of size engineering and associated magnetic field effects interplay to produce the largest lowering in Rct at Hext=200 mT. A comprehensive analysis of electrocatalytic parameters including the Tafel slope and double layer capacitance establishes further insights on co-relation of size effect and magnetic properties to understand the role of nanocarbon supported transition metal oxides in water electrolysis.

In situ investigation of ruthenium doped lanthanum nickel titanium double perovskite and its exsolution behaviour

Exsolution, an innovative method for fabricating perovskite-based oxides decorated with metal nanoparticles, has garnered significant interest in the fields of catalyst fabrication and electrochemical devices. Although dopant exsolution from single perovskite structures has been extensively studied, the exsolution behaviour of double perovskite structures remains insufficiently understood. In this study, we synthesized B-site double perovskite Ru-doped lanthanum nickel titanates with a 7.5 at% A-site deficiency, and systematically investigated the exsolution process that formed nickel metal nanoparticles on the material surface, across a broad reduction temperature range of 350-1000 °C. Both Ex situ and in situ characterization revealed that small, uniform Ni nanoparticles exsolved at low temperatures, whereas the exsolution of ruthenium required higher reduction temperatures beyond 1000 °C. Within the reduction temperature range of 350-500 °C, a notable finding is the reconstruction of exsolved nanoparticles, implying that Ni particles exist in a thermodynamically metastable state. Electrochemical impedance spectroscopy (EIS) showed a decreased area specific resistance (ASR) during the progress of exsolution. The increase in current density of a full solid oxide cell (SOC) in electrolysis mode and the doubling of peak power density in fuel cell mode attributed to the exsolution of Ni nanoparticles highlight the potential application of metal exsolution in electrode materials for SOCs.

Exfoliation of Ca3Co4O9 to Two-Dimensional Single-Crystalline Misfit Calcium Cobaltates for Energy Storage Applications

Layered materials have become indispensable in the development of two-dimensional (2D) systems, offering extensive specific surface area and exceptional electrical, electrochemical, and optical properties critical for diverse applications in energy storage, catalysis, sensing, and optoelectronics. While mono- and biatomic layered materials have demonstrated remarkable characteristics in lower dimensions, the quest for complexity in materials has opened new avenues for tailoring properties to specific requirements. Within this context, misfit-layered compounds (MLCs) stand out as promising candidates. In this study, we present a successful synthesis of few-layered misfit CaCoO2-CoO2 2D nanosheets in bulk quantities from bulk calcium cobalt oxide (CCO-B or CCO). These newly synthesized 2D exfoliated misfit nanosheets demonstrate remarkable 7-fold electrochemical energy storage properties, surpassing their parent bulk CCO, as cathode materials in aqueous Zn-ion batteries. This work addresses the longstanding challenge of exfoliating bulk MLCs to nanostructured, lower dimensional MLCs, opening doors for utilization in advanced energy storage systems and beyond.

Cobalt-doped copper vanadate: a dual active electrocatalyst propelling efficient H2 evolution and glycerol oxidation in alkaline water

Strategically doped metal oxide nanomaterials signify a rapidly growing genre of functional materials with a wide range of practical applications. Copper vanadate (CuV) represents one such highly active system, which has been rarely explored following its doping with an abundant first-row transition metal. Here, we have developed a series of CuV samples with varying cobalt(ii) doping concentrations deploying a relatively simple solid state synthetic procedure. Among the samples, the 10% Co(ii)-doped CuV (Co_10%-CuV) exhibited excellent reactivity for both the H₂ evolution reaction (HER) and glycerol oxidation reaction (GOR) in an alkaline aqueous medium (pH 14.0) during cathodic and anodic scans, respectively. During this dual-active catalysis, surface-immobilized Co_10%-CuV operates at exceptionally low overpotentials of 176 mV and 160 mV for the HER and GOR, respectively, while achieving 10 mA cm² current density. The detailed spectroscopic analysis revealed the formation of formate as the major product during the GOR with a faradaic efficiency of >90%. Therefore, this Co_10%-CuV can be included on either side of a two-electrode electrolyzer assembly to trigger a complete biomass-driven H₂ production, establishing an ideal carbon-neutral energy harvest process.

Exsolution-Driven Surface Transformation in the Host Oxide

Exsolution synthesizes self-assembled metal nanoparticle catalysts via phase precipitation. An overlooked aspect in this method thus far is how exsolution affects the host oxide surface chemistry and structure. Such information is critical as the oxide itself can also contribute to the overall catalytic activity. Combining X-ray and electron probes, we investigated the surface transformation of thin-film SrTi_0.65Fe_0.35O₃ during Fe⁰ exsolution. We found that exsolution generates a highly Fe-deficient near-surface layer of about 2 nm thick. Moreover, the originally single-crystalline oxide near-surface region became partially polycrystalline after exsolution. Such drastic transformations at the surface of the oxide are important because the exsolution-induced nonstoichiometry and grain boundaries can alter the oxide ion transport and oxygen exchange kinetics and, hence, the catalytic activity toward water splitting or hydrogen oxidation reactions. These findings highlight the need to consider the exsolved oxide surface, in addition to the metal nanoparticles, in designing the exsolved nanocatalysts.

Analysis of Performance Losses and Degradation Mechanism in Porous La2-X NiTiO6-δ:YSZ Electrodes

The electrode performance and degradation of 1:1 La_2−xNiTiO_6−δ:YSZ composites (x = 0, 0.2) has been investigated to evaluate their potential use as SOFC cathode materials by combining electrochemical impedance spectroscopy in symmetrical cell configuration under ambient air at 1173 K, XRD, electron microscopy and image processing studies. The polarisation resistance values increase notably, i.e., 0.035 and 0.058 Ωcm² h⁻¹ for x = 0 and 0.2 samples, respectively, after 300 h under these demanding conditions. Comparing the XRD patterns of the initial samples and after long-term exposure to high temperature, the perovskite structure is retained, although La₂Zr₂O₇ and NiO appear as secondary phases accompanied by peak broadening, suggesting amorphization or reduction of the crystalline domains. SEM and TEM studies confirm the ex-solution of NiO with time in both phases and also prove these phases are prone to disorder. From these results, degradation in La_2−xNiTiO_6−δ:YSZ electrodes is due to the formation of La₂Zr₂O₇ at the electrode–electrolyte interface and the ex-solution of NiO, which in turn results in the progressive structural amorphization of La₁₈NiTiO_6−δ phases. Both secondary phases constitute a non-conductive physical barrier that would hinder the ionic diffusion at the La_2−xNiTiO_6−δ:YSZ interface and oxygen access to surface active area.