Photoelectrochemical photocurrent switching effect on a pristine anodized Ti/TiO2 system as a platform for chemical logic devices

Self-Powered FTO/CdSe/Bi2Se3 Photodetector with Bipolar Photoresponse Characteristics

Self-powered photodetectors with bipolar photoresponse characteristics are expected to play a critical role in the field of secure optical communication, artificial neuromorphic systems, and intelligent color sensors. In this work, asymmetric heterojunction devices exhibiting wavelength-dependent bipolar photoresponse with a structure of Glass/FTO/CdSe/Bi2Se3/Au were fabricated. Under a short wavelength light irradiation, the top CdSe absorber generates a high carrier concentration; the excited carriers are quickly separated by the built-in electric field induced by the FTO/CdSe diode, resulting in a negative photocurrent. For light with wavelengths beyond the CdSe absorption edge, it is absorbed by the bottom Bi2Se3 absorber, and a positive photocurrent can be observed. Therefore, based on the bandgap difference between the top CdSe absorber and the bottom Bi2Se3 absorber, combined with the photogenerated carriers separated by asymmetric back-to-back diode, a wavelength-dependent bipolar response is realized. In this work, by employing this structure, the responsivities of -33.3 and 0.3 mA/W were achieved under the illumination of 405 and 830 nm, respectively. This work provides important indications in the preparation and performance optimization for wavelength-dependent bipolar photodetectors.

Actively Driven Light-Addressable Sensor/Actuator System for Automated pH Control for the Integration in Lab-On-A-Chip (LoC) Platforms

The miniaturization of microfluidic systems usually comes at the cost of more difficult integration of sensors and actuators inside the channel. As an alternative, this work demonstrates the embedding of semiconductor-based sensor and actuator technologies that can be spatially and temporally controlled from outside the channel using light. The first element is a light-addressable potentiometric sensor, consisting of an Al/Si/SiO2/Si3N4 structure, that can measure pH changes at the Si3N4/electrolyte interface. The pH value is a crucial factor in biological and chemical systems, and besides measuring, it is often important to bring the system out of equilibrium or to adjust and control precisely the surrounding medium. This can be done photoelectrocatalytically by utilizing light-addressable electrodes. These consist of a glass/SnO2:F/TiO2 structure, whereby direct charge transfer between the TiO2 and the electrolyte leads to a pH change upon irradiation. To complement the advantages of both, we integrated a light-addressable sensor with a pH sensitivity of 41.5 mV·pH-1 and a light-addressable electrode into a microfluidic setup. Here, we demonstrated a simultaneous operation with the ability to generate and record pH gradients inside a channel under static and dynamic flow conditions. The results show that dependent on the light-addressable electrode (LAE)-illumination conditions, pH changes up to ΔpH of 2.75 and of 3.52 under static and dynamic conditions, respectively, were spatially monitored by the light-addressable potentiometric sensor. After flushing with fresh buffer solution, the pH returned to its initial value. Depending on the LAE illumination, pH gradients with a maximum pH change of ΔpH of 1.42 were tailored perpendicular to the flow direction. In a final experiment, synchronous LAE illumination led to a stepwise increase in the pH inside the channel.

Electrolyte-Controlled Photoelectrochemical Photocurrent Switching Effect in High-Performance Self-Powered Broadband Photoelectrochemical-Type Photodetectors Based on MnPS3 Nanosheets

Photoelectric devices are extensively applied in optical logic systems, light communication, optical imaging, and so on. However, traditional photoelectric devices can only generate unidirectional photocurrent, which hinders the simplification and multifunctionality of devices. Recently, it has become a new research focus to achieve controllable reversal of the output photocurrent direction (bipolar current) in a photoelectric system. Considering that the device with bipolar current adds a reverse current operating state compared to traditional devices, the former is more suitable for developing new multifunctional photoelectric devices. Due to the existence of electrolytes, photoelectrochemical (PEC) systems contain chemical processes such as ion diffusion and migration and electrochemical reactions, which are unable to occur in solid-state transistor devices, and the effect of electrolyte pH on the performance of PEC systems is usually ignored. We prepared a MnPS3-based PEC-type photodetector and reversed photocurrents by adjusting the pH of electrolytes, i.e., the electrolyte-controlled photoelectrochemical photocurrent switching (PEPS) effect. We clarified the effect of pH values on the direction of photocurrent from the perspectives of electrolyte energy level rearrangement splitting and the kinetic theory of the semiconductor electrode. This work not only contributes to a deeper understanding of carrier transport in PEC processes but also inspires the development of advanced multifunctional photoelectric devices.

Size-Independent Reconfigurable Logic Gate with Bismuth Oxide Based Photoelectrochemical Device

XOR gate, an important building block in computational circuits, is often constructed by combining other basic logic gates, and the hybridity inevitably leads to its complexity. A photoelectrochemical device could realize XOR function based on the current change of the photoelectrode; however, such signal is highly sensitive to photoelectrode size and therefore requires precise manufacturing at a high cost. Herein we developed a novel XOR gate based on the light-induced open-circuit potential (OCP) of the Bi₂O₃ photoelectrode. Surprisingly, the OCP of Bi₂O₃ does not increase with light intensity according to the traditional logarithmic relationship. Instead, an unusual decrease in OCP is observed at high light intensity, which is attributed to the dramatic light-induced increase in surface states that can be easily regulated by varying the oxygen partial pressure during reactive magnetron sputtering. Based on such a nonmonotonic variation of OCP, a facile Bi₂O₃-based gate is designed to realize the XOR function. Unlike the commonly used current signal, OCP is size independent, and therefore, the Bi₂O₃-based gate does not require high manufacturing accuracy. Moreover, in addition to XOR, the Bi₂O₃-based PEC gate also demonstrates great versatility in realizing other logic functions including AND, OR, NOT, NIH, NAND, and NOR. The strategy of modulating and applying nonmonotonic OCP signal opens a new avenue for designing size-independent reconfigurable logic gates at low manufacturing cost.

Construction of unique heterojunction photoanodes through in situ quasi-epitaxial growth of FeVO4 on Fe2O3 nanorod arrays for enhanced photoelectrochemical performance

By enhancing the separation of photogenerated electron–hole pairs, reducing carrier recombination and the impedance of the interface electrolyte, the FeVO4–Fe2O3 photoanode exhibits obviously enhanced photoelectrochemical performance.

Infochemistry and the Future of Chemical Information Processing

Nowadays, information processing is based on semiconductor (e.g., silicon) devices. Unfortunately, the performance of such devices has natural limitations owing to the physics of semiconductors. Therefore, the problem of finding new strategies for storing and processing an ever-increasing amount of diverse data is very urgent. To solve this problem, scientists have found inspiration in nature, because living organisms have developed uniquely productive and efficient mechanisms for processing and storing information. We address several biological aspects of information and artificial models mimicking corresponding bioprocesses. For instance, we review the formation of synchronization patterns and the emergence of order out of chaos in model chemical systems. We also consider molecular logic and ion fluxes as information carriers. Finally, we consider recent progress in infochemistry, a new direction at the interface of chemistry, biology, and computer science, considering unconventional methods of information processing.

Enhanced performance and degradation of wastewater in microbial fuel cells using titanium dioxide nanowire photocathodes

This paper explores the decolorization of dye wastewaters and electricity generation using dual-chamber microbial fuel cells (MFCs) with titanium dioxide nanowire (TiO2 NW) photocathodes. TiO2 NW cathodes under ultraviolet light are observed to enhance the reduction of azo dye Active Red 30 (AR 30) and electricity generation. The analysis of electrochemical impedance spectra (EIS) indicates acceleration of the electron transfer processes of photoelectrode reduction by the photocatalysis of TiO2 NWs, with polarization resistance of the photocathode being 10.45 Ω under light irradiation from 294 Ω in the dark. Ultraviolet-visible light spectroscopy shows that the maximum degradation of the MFCs is 78.1%; the azo bond of AR 30 may be cleaved by photoelectrons generated by light irradiation of the illuminated TiO2 NW photocathode. The electricity produced by microbial fuel cells (MFCs) is expected to enhance the reductive decolorization of the azo dye AR 30 solution.

Nanoparticles in Polyelectrolyte Multilayer Layer-by-Layer (LbL) Films and Capsules—Key Enabling Components of Hybrid Coatings

Originally regarded as auxiliary additives, nanoparticles have become important constituents of polyelectrolyte multilayers. They represent the key components to enhance mechanical properties, enable activation by laser light or ultrasound, construct anisotropic and multicompartment structures, and facilitate the development of novel sensors and movable particles. Here, we discuss an increasingly important role of inorganic nanoparticles in the layer-by-layer assembly—effectively leading to the construction of the so-called hybrid coatings. The principles of assembly are discussed together with the properties of nanoparticles and layer-by-layer polymeric assembly essential in building hybrid coatings. Applications and emerging trends in development of such novel materials are also identified.