The oxygen reduction reaction (ORR) is the rate-limiting reaction in the cathode side of fuel cells. In the quest for alternatives to Pt-electrodes as cathodes in ORR, appropriate transition metal oxide-based electrocatalysts are needed. In the present work, we have synthesized Co₃O₄ and CoO/Co₃O₄ nanostructures using flame spray pyrolysis (FSP), as electrocatalysts for ORR in acidic and alkaline media. A detailed study of the effect of (Co-oxide)/Pt ratio on ORR efficiency shows that the present FSP-made Co-oxides are able to perform ORR at very low-Pt loading, 0.4% of total metal content. In acid medium, an electrode with (5.2% Pt + 4.8% Co₃O₄), achieved the highest ORR performance (J_max = 8.31 mA/cm², E_1/2 = 0.66 V). In alkaline medium, superior performance and stability have been achieved by an electrode with (0.4%Pt + 9.6% (CoO/Co₃O₄)) with ORR activity (J_max = 3.5 mA/cm², E_1/2 = 0.08 V). Using XRD, XPS, Raman and TEM data, we discuss the structural and electronic aspects of the FSP-made Co-oxide catalysts in relation to the ORR performance. Cyclic voltammetry data indicate that the ORR process involves active sites associated with Co³⁺ cations at the cobalt oxide surface. Technology-wise, the present work demonstrates that the developed FSP-protocols, constitutes a novel scalable process for production of co-oxides appropriate for oxygen reduction reaction electrodes.

Cu-oxide nanophases (CuO, Cu₂O, Cu⁰) constitute highly potent nanoplatforms for the development of efficient Artificial Photosynthesis catalysts. The highly reducing conduction band edge of the d-electrons in Cu₂O dictates its efficiency towards CO₂ reduction under sunlight excitation. In the present review, we discuss aspects interlinking the stability under photocorrosion of the (CuO/Cu₂O/Cu⁰) nanophase equilibria, and performance in H₂-production/CO₂-reduction. Converging literature evidence shows that, because of photocorrosion, single-phase Cu-oxides would not be favorable to be used as a standalone cathodic catalyst/electrode; however, their heterojunctions and the coupling with proper partner materials is an encouraging approach. Distinction between the role of various factors is required to protect the material from photocorrosion, e.g., use of hole scavengers/electron acceptors, band-gap engineering, nano-facet engineering, and selectivity of CO₂-reduction pathways, to name a few possible solutions. In this context, herein we discuss examples and synthesis efforts that aim to clarify the role of interfaces, faces, and phase stability under photocatalytic conditions.

Palladium is among the most versatile noble-metal atoms that, when dispersed on solid supports, can be stabilized in 0, +1, +2, +3 redox states. Moreover, despite its noble-metal character, Pd shows a considerable degree of chemical reactivity. In Pd Nanoparticles (NPs), atomic {Pdⁿ⁺-X} states, where n = 0, 1, 2, 3, and X = atom or hydride, can play key roles in catalytic processes. Pd-oxygen moieties can be stabilized at nanointerfaces of Pd in contact with metal-oxides. These {Pdⁿ⁺-X}s can be either isolated Pd atoms dispersed on the support, or, more interestingly, atomic states of Pd occurring on the Pd NPs. The present review focuses on the role of such {Pdⁿ⁺-X} states in catalytic processes related to energy storage or energy conversion, with specific focus on photocatalysis, H₂ production reaction (HRR), oxygen reduction reaction (ORR), and water-splitting. Synthesis of atomic {Pdⁿ⁺-X} states and their detection methodology is among the current challenges. Herein, the chemistry of {Pdⁿ⁺-X} states on Pd- [metal oxide] interfaces, methods of detection, and identification are discussed. The implication of {Pdⁿ⁺-X} in transient catalytic intermediates is reviewed. Finally, the role of {Pdⁿ⁺-X} in photo electrocatalytic processes is critically discussed.

The provenance of marbles can be probed, based on correlation between the EPR parameter ( D ) of Mn ²⁺ -ions in marbles, and lattice-macrostrain ( ε ₀ ) of marble crystal, obtained by high-resolution XRD.

The development of durable heterogenized molecular catalysts based on earth-abundant metals remains a key challenge for sustainable Η2- production via Formic Acid Dehydrogenation (FADH), due to catalyst deactivation during prolonged operation. Herein, robust {SiO2–triazine}@[PNP-Fe] heterogeneous catalysts were developed via covalent immobilization of molecular [Fe– Pincer PNP], catalyst on a {SiO2–triazine} support. The catalytic performance was fine-tuned by incorporation of a PP₃-phosphine as co-ligand, therefore the {SiO2–triazine}@[PNP-Fe]/ PP₃} hybrid system combined the activity of homogeneous catalysts with the robustness and recyclability of heterogeneous systems. Two PNP-immobilization strategies, and two Pincer-PNP ligands, iProPNP and tBuPNP with different steric properties, were systematically investigated to establish structure–performance relationships. Among the prepared materials, the directly-immobilized {SiO2–triazine}@[iProPNP-Fe]/PP₃} catalyst exhibited the highest FADH activity, producing 86.4 L of H₂/CO₂, achieving a total turnover number of 235,535. This hybrid shows significant robustness maintaining FADH-catalytic activity for 61 h over two consecutive cycles. Mechanistic studies revealed that catalyst deactivation is governed primarily by gradual depletion and protonation of the mobile PP₃ co-ligand, rather than degradation of the {SiO2–triazine}@[PNP-Fe] catalyst. Guided by this finding, periodic PP₃ replenishment was implemented as an operational strategy that continuously regenerated catalytically active Fe-species and significantly prolonged catalyst lifetime for >60h. These findings establish {SiO2–triazine} hybrid materials as robust platform for heterogenized molecular Fe catalysts and demonstrate that dynamic co-ligand management provides a general strategy for extending the lifetime of immobilized molecular catalysts.