Chun-Hu Chen

Synthesis of multinary perovskite oxides is often limited by unstable phase formation and uncontrolled metal incorporation. Acidic redox‐assisted precipitation (ARP) offers stoichiometric redox control but has historically produced spinel or amorphous oxides rather than ABO ₃ phases. Here we show that introducing citric acid redirects ARP into a phase‐selective, perovskite‐forming pathway, enabling the synthesis of phase‐pure La–Co–Mn oxides. Phase selection arises from competition between Co ²⁺ –MnO ₄ ⁻ oxidation and citric‐acid‐to‐MnO ₄ ⁻ reduction, establishing a redox stoichiometric window and enabling reaction‐selective metal incorporation that yields an A:B ratio approaching 1:1. The final composition reflects composition selection rather than precursor replication, revealing a previously unrecognized dimension of redox‐governed phase selection in multimetal oxide synthesis.

Nitrogen-doped graphene holds immense promise for electrocatalysis, where surpassing the traditional 2–5 at% nitrogenation ceiling requires strategic control of thermodynamic and kinetic factors. Here, we systematically investigate the dominant thermodynamic and kinetic parameters to reach higher nitrogenation. It is demonstrated that, within the investigated 140–200 °C hydrothermal regime, neither kinetic nor mass-transport limitations matter, in sharp contrast to the prevailing literature. Instead, nitrogenation levels are fundamentally governed by the population of basal-plane epoxide groups, meaning that the starting graphene oxide oxidation degree alone limits ultimate doping efficiency. Optimizing precursor oxidation successfully drives the final nitrogen content to 17.3 at% (N/C = 0.24). Subsequent thermal treatment efficiently converts this grafted nitrogen into lattice-doped configurations dominated by pyridinic N (57%). This work establishes a framework showing that maximizing reactive oxygen sites is the definitive pathway to advanced nitrogen-doped frameworks.

Controlling phase selectivity for especially metastable multimetal oxides remains a central challenge, even though they are attractive for catalysis and energy conversion applications. The conventional synthesis method, like aqueous redox-precipitation, typically uses dilute reactant solutions, in which thermodynamic equilibrium favors stable products, limiting the selective synthesis of metastable phases. Here, we demonstrate a water-assisted reaction that plays a dual and decisive role in liquid-assisted redox synthesis (LRS) to obtain a metastable tetragonal cobalt–manganese spinel (CMO), rather than the readily formed cubic spinel. Limited initial hydration (0.5–1.5 mL) creates a highly concentrated microenvironment that enhances local acidity and shifts redox toward Mn3+ formation rather than Mn4+. Dehydration at 160 °C enables the incorporation of unstable Mn3+ into the solid lattice, resulting in high selectivity and phase purity toward the metastable tetragonal spinel. A low liquid-to-solid ratio (η = 0.27–0.81 μL mg–1) coupled with elevated dehydration temperatures (up to 200 °C) enabled the selective formation of metastable tetragonal spinel. Increasing the initial water content (≥3.0 mL) without complete water dehydration further restores bulk-solution-like behavior, promotes Mn3+/Mn4+ equilibration, and yields the thermodynamic cubic spinel. The optimized condition delivers 88% yield (∼27× higher than conventional aqueous ARP, 3.2%), and the tetragonal phase exhibits enhanced alkaline (oxygen evolution reaction) OER activity relative to the cubic analog.

Interfacial engineering of photoanodes is essential for efficient solar water splitting; however, many existing strategies rely on complex, multistep processes or hydrothermal growth, limiting scalability and reproducibility. Here, we present a universal interfacial engineering platform based on a sub-2 min acidic redox-assisted deposition (ARD) of an amorphous inorganic binder, cobalt-manganese oxyhydroxide (CMOH). Using two-step-fabricated BiVO₄ as a literature-standard benchmark, we demonstrate that an ultrathin CMOH overlayer markedly enhances photoelectrochemical (PEC) water oxidation performance. The conformal CMOH coating (∼3.5 nm) is deposited under ambient conditions via a simple dip-coating process and is broadly applicable to metal oxide photoanodes, including BiVO₄, WO₃, and ZnO. The CMOH-modified BiVO₄ photoanode delivers a high photocurrent density of ∼6.0 mA cm^-2 and a hole-transfer efficiency of ∼82% at 1.23 V_RHE, together with a remarkable applied bias photon-to-current efficiency (ABPE) of 1.68% at 0.66 V_RHE. These enhancements originate from effective surface-state passivation by the CMOH overlayer, leading to over a 4-fold reduction in the surface recombination rate constant, as revealed by intensity-modulated photocurrent spectroscopy (IMPS). In addition, the reduced Tafel slope (78.5 mV dec^-1) suggests that the CMOH layer promotes interfacial charge transfer and enhances the water oxidation kinetics of the BiVO₄ photoanode. This work elucidates the critical role of amorphous CMOH oxygen evolution catalysts in mediating photoinduced charge-carrier dynamics and establishes a facile and scalable strategy to broadly enhance the PEC performance of metal oxide photoanodes for large-scale solar fuel production.

Surface reconstruction, although often associated with enhanced activity through the lattice oxygen mechanism (LOM), can expose vulnerable sites that accelerate chloride‐induced corrosion. It is demonstrated that a silver and cerium co‐doped iron manganese oxide catalyst achieves high oxygen evolution reaction (OER) activity while maintaining a stable, reconstruction‐free surface under alkaline seawater conditions. Operando X‐ray absorption spectroscopy (XAS), complemented by the previous operando Raman analysis, reveals no detectable rearrangement of chemical environment or electronic structures across the OER‐relevant potential window. The catalyst achieves a low overpotential of 210 mV to reach 10 mA cm ⁻² in alkaline seawater, while maintaining 99.5% faradaic efficiency for oxygen evolution. By adopting the electrocatalyst into an anion exchange membrane (AEM) electrolyzer (5×5 cm ² of active area) for direct seawater electrolysis, the durability tests show a stable electrolysis current of 5000 mA for at least 250 h, while the blank electrolyzer fails in 1 h with significant corrosion. These findings strongly support the hypothesis that inhibiting surface reconstruction can effectively enhance seawater corrosion resistance without sacrificing catalytic performance.

The acidic redox-assisted deposition (ARD) of cobalt manganese oxyhydroxides (CMOH) as a solid-state inorganic binder has been demonstrated. CMOH is stable and highly adhesive under high oxidative currents during OER tests.

Traditional screen printing is an easy approach commonly used for conductive pattern fabrication of electronics but lacks high resolution. Photolithography offers better resolution but is complex. Photosensitive silver pastes (PSP) combine the benefits of both but suffer from undercut issues, causing uneven etching, decreased interfacial adhesion, and thus poor resolutions. In this study, we explore the use of molecular precursors (i.e., silver oxalate) to replace metallic silver particles and enhance the depth of light penetration. Our findings demonstrate a successful solution to the undercut issue, achieving an undercut index of 1.0, indicating an undercut-free scenario and enabling higher resolutions in line and pattern formation. Additionally, our research confirms the feasibility of multilayer stacking of photosensitive pastes, achieving unprecedented aspect ratios in line patterns. By replacing 25% of micrometer silver powder with silver oxalate (PSP-25), we achieved optimal line widths as fine as 10 μm. The three-layer stack of PSP-25 reached a substantial aspect ratio with a height of 29.4 μm and an optimal fringe pattern resolution of 10 μm line width with a 15 μm aisle width. Utilization of silver oxalate was observed to slightly expand the line width, likely due to light scattering by the fine silver nanoparticles (∼40 nm) formed during the photodecomposition of silver oxalate.