Physics

ABSTRACT Hydrogen peroxide (H 2 O 2 ) is a prototypical green oxidant with wide applications. In pursuit of sustainable development, H 2 O 2 electrosynthesis via the two‐electron oxygen reduction reaction (2e − ORR) under mild, green, and decentralized conditions has emerged as a promising alternative to the industrial anthraquinone process. H 2 O 2 electrosynthesis is an interfacial electrochemical process in which appropriate surface active sites are critical for achieving high performance. To realize scalable H 2 O 2 production via 2e − ORR, in situ optical characterization is crucial for elucidating interfacial mechanisms and reaction principles, thereby facilitating further technological advances. This review is organized around the progressive enhancement of spatial resolution and accessible reaction information, and systematically summarizes in situ optical characterization methods for H 2 O 2 electrosynthesis via 2e − ORR, spanning one‐dimensional (1D) spectroscopy, two‐dimensional (2D) imaging, three‐dimensional (3D) reaction‐field imaging, and multimodal coupling that correlates optical, electrochemical, and structural information. It highlights the working principles, device configurations, and representative applications of these methods, and provides perspectives on future technological innovation and practical application of in situ optical characterization for advancing sustainable and economically viable H 2 O 2 electrosynthesis in support of green industry and carbon neutrality.

Acquiring and processing full-motion details in machine vision typically consumes a substantial amount of energy. In contrast, a hierarchical processing architecture, combining a low-power standby front end with an on-demand activated back end, provides an optimized energy-performance tradeoff. To achieve this, the complete acquisition and decoupling of static (brightness) and dynamic (amplitude and polarity) output at the sensory level are essential for activating on-demand vision function. Here, we report a differential image sensor (DIS) that leverages differential photodiodes with decoupled differential and tunneling modes. These modes can be read out via conventional ROICs, paving the way for the up-scaled integration (e.g., 640 × 512). With on-demand activated dynamic and static modes, the DIS implements a hierarchical motion-processing pipeline-from sparse motion detection to optical flow and depth analysis. This work provides a power-efficient and scalable strategy for advancing vision-based AIoT applications.

Real-world visual scenes include wide illumination conditions with rapid fluctuations, demanding vision sensors that integrate multiple visual dynamics through diverse modulation strategies. However, most vision sensors suffer from limited tunability, mainly modulated via external physical stimuli (e.g., electric or light) while lacking chemical programmability critical for biorealistic vision. Here, we report a chemically programmable retinomorphic p-n diode that supports spiking response and light adaptation together with chemical tunability in an ultracompact device platform. Governed by the interplay between photoelectric carrier separation at the internal p-n junction and electrochemical carrier consumption at the semiconductor/electrolyte interface, the retinomorphic diode demonstrates switchable response modes with chemical programmability. Specifically, the device generates spikes upon illumination transitions under closed-circuit operation, while varying ion/molecule species enables bidirectional tuning of steady-state current, transforming dynamic-only sensing into static-dynamic fused sensing. Moreover, it spontaneously shifts from scotopic to photopic adaptation with increasing illumination under open-circuit operation, while both processes can be bidirectionally regulated through chemical programming. Leveraging this adaptive behavior, we further construct a proof-of-concept visual-motor pathway that exhibits chemically programmable, illumination-dependent actuation. Together, this work demonstrates a chemically programmable retinomorphic platform combining physical and chemical modulation for bioinspired multimode visual sensing.

In the present work, nanoparticles of CdS and ZnO were synthesized using the coprecipitation method, and their respective composites were formed using an ultrasonic technique with varying ZnO concentrations. The effect of ZnO concentration enhancement on the structural, electrical, and optical properties of CdS/ZnO composites has been studied. The X‐ray spectroscopy and Raman spectroscopy confirm the formation of CdS and ZnO nanoparticles and their composites. X‐ray diffraction spectroscopy (XRD) has been used to study the structural properties of CdS, ZnO nanoparticles, and their composites. The coexistence of the planes corresponds to both CdS and ZnO nanoparticles in the XRD diffractogram of nanocomposites, confirming the formation of the composites. Linear absorption properties of the material are studied with the help of UV–Visible (UV–Vis) spectroscopy and photoluminescence spectroscopy (PL). The bandgap of nanoparticles and their respective composites has been studied using Tauc's Plots. The bandgap calculated from the UV–Vis spectra first increases and then decreases with a rise in ZnO concentration in the composites discussed in UV–Vis section. The KEITHLEY 6517A electrometer is used to study the electrical properties of these materials, which show a rise in current with an enhancement in ZnO concentration at a fixed voltage. The results obtained from the current–voltage characteristics are in good agreement with the UV–Vis spectroscopy analysis. In this work, we tuned the optical properties of CdS/ZnO nanocomposites can be tuned by varying the ZnO composition in the nanocomposites. Moreover, the composites have enhanced visible light adsorption capacity, which extends their use in photocatalytic applications. Findings from various characterizations are consistent with each other.

Increasing Fe concentration from 0.1 to 1.0 wt% strongly modifies the magnetic behavior of β1′ martensitic Cu–Al alloys. Enhanced magnetization, coercivity, and remanence indicate increasingly pronounced Fe-related magnetic interactions. Magnetic and EPR measurements reveal the emergence of collective magnetic behavior and low-temperature magnetic freezing.

The magnetic properties of nanocrystalline Cu–Al–Fe alloys with a dilute Fe concentration of 0.1–1.0 wt% were investigated. PXRD shows that the alloys are dominated by the β1ʹ martensitic phase, while the lattice microstrain slightly increases with increasing Fe content. The 0.1 wt% Fe alloy exhibits weak, nearly reversible magnetization characteristic of a magnetically soft system. Increasing the Fe concentration to 1.0 wt% leads to higher magnetization, finite coercivity and remanence, along with the appearance of ZFC‐FC irreversibility with a blocking‐like maximum near 7 K. X‐band EPR spectra reveal contributions from both isolated Fe 3+ ions and exchange‐coupled Fe‐related magnetic centers. The low‐field microwave absorption signal observed in the 0.1 wt% Fe alloy disappears as the Fe concentration increases. An anomaly in EPR parameters for Fe‐related paramagnetic centers near 25 K indicates changes in spin dynamics associated with Fe–Fe interactions. The magnetic behavior is attributed to Fe atoms incorporated into the martensitic lattice.

Copper oxides are promising photocathodes for solar hydrogen production, but the role of the metastable intermediate phase, paramelaconite (Cu 4 O 3 ), remains obscure due to its narrow thermodynamic stability window. Herein, we report the controllable synthesis of pure Cu 2 O, Cu 4 O 3 and CuO thin films via radio-frequency reactive magnetron sputtering by precisely manipulating the oxygen partial pressure. A systematic phase diagram was established to isolate the challenging Cu 4 O 3 phase, facilitating comprehensive comparative studies of the inherent correlations between crystal structure, electronic properties, and photoelectrochemical (PEC) behaviors. Mott-Schottky plots and band alignment analysis reveal that Cu 2 O exhibits the most favorable electronic properties, featuring the highest hole carrier density (∼ 3.1 × 10 19 cm −3 ) and the most negative conduction band potential, providing the strongest thermodynamic driving force for hydrogen evolution. In contrast, although the Cu 4 O 3 also demonstrates a high carrier density (∼ 2.7 × 10 19 cm −3 ), comprehensive PEC evaluations identify its rapid surface recombination and significant photocorrosion. This stems from a high density of deep-level traps acting as recombination centers, which drives severe surface charge recombination and consequently triggers rapid photocorrosion. Conversely, the Cu 2 O phase shows superior kinetic stability with rectangular photoresponses and distinctive self-activation behavior. This work unravels the trade-off between conductivity and stability, affirming that the defect tolerance and phase purity of Cu 2 O render it as the optimal candidate material for durable solar water splitting.