The role of relative rate constants in determining surface state phenomena at semiconductor–liquid interfaces

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.

Contact Electrification at the Liquid-Solid Interface

Interfaces between a liquid and a solid (L-S) are the most important surface science in chemistry, catalysis, energy, and even biology. Formation of an electric double layer (EDL) at the L-S interface has been attributed due to the adsorption of a layer of ions at the solid surface, which causes the ions in the liquid to redistribute. Although the existence of a layer of charges on a solid surface is always assumed, the origin of the charges is not extensively explored. Recent studies of contact electrification (CE) between a liquid and a solid suggest that electron transfer plays a dominant role at the initial stage for forming the charge layer at the L-S interface. Here, we review the recent works about electron transfer in liquid-solid CE, including scenerios such as liquid-insulator, liquid-semiconductor, and liquid-metal. Formation of the EDL is revisited considering the existence of electron transfer at the L-S interface. Furthermore, the triboelectric nanogenerator (TENG) technique based on the liquid-solid CE is introduced, which can be used not only for harvesting mechanical energy from a liquid but also as a probe for probing the charge transfer at liquid-solid interfaces.

Qualitative Approaches Towards Useful Photocatalytic Materials

The long-standing crusade searching for efficient photocatalytic materials has resulted in a vast landscape of promising photocatalysts, as reflected by the number of reviews reported in the last decade. Virtually all of these reviews have focused on quantitative approaches aiming at developing an understanding of the underlying mechanisms behind photocatalytic behavior and the parameters that influence structure–function correlation. Less attention has been paid, however, to qualitative measures around the development and assessment of photocatalysts. These measures will contribute toward narrowing the range of potential photocatalytic materials for widespread applications. The current report provides a critical perspective over some of the main factors affecting the assessment of photocatalytic materials as a code of good practice. A case of study is also provided, where this qualitative analysis is applied to one of the most prolific materials of the last-decade, disorder-engineered, black titanium dioxide (TiO₂).

Interpreting interfacial semiconductor-liquid capacitive characteristics impacted by surface states: a theoretical and experimental study of CuGaS2

Semiconductor-liquid interfaces are essential to the operation of many energy devices. Crucially, the operational characteristics of such devices are dependent upon both the flat band potential and doping concentration present in their solid-state semiconducting region. Traditionally, capacitive "linear" Mott-Schottky plots have often been utilized to extract these two parameters. However, significant concentrations of surface states within semiconductor-liquid junctions can give rise to strong non-linearities that prevent an effective linearity-based analysis. In this work, we detail a theoretical approach for estimating both the doping concentration and flat band potential from the capacitive characteristics of semiconductor-liquid junctions heavily impacted upon by surface states. Our theoretical approach is applied to CuGaS2 immersed in an aqueous electrolyte, for which excellent convergent values of the doping concentration and flat band potential are obtained across a wide range of impedance measurement frequencies. The results suggest a marked improvement over a linearity-based approach that could assist the analysis of many types of semiconductor-liquid junctions subject to high concentrations of surface states.

Understanding the enhanced photoelectrochemical water oxidation over Ti-doped α-Fe2O3 electrodes by electrochemical reduction pretreatment

Water splitting using semiconductor photoelectrodes is a promising approach to solar hydrogen production. Previous studies have well-demonstrated that electrochemical reduction (ER) pretreatment of bare and Ti-doped α-Fe2O3 electrodes enhances water photooxidation efficiencies, however, the mechanism underlying this improvement remains poorly understood. In this study, this was quantitatively investigated by multiple photoelectrochemical techniques and transient absorption spectroscopy, using the doped electrodes as examples. The results reveal that the kinetics of photoholes after moving to the electrode surface can be well described by a model of surface-state mediated charge transfer and recombination. The reason for the photocurrent enhancement is attributed to a significantly increased charge transfer rate constant (kct) and a decreased surface recombination rate constant (ksr) by ER. The reason for the accelerated kct is that a new type of surface state, with a favorable energy position for water oxidation, is produced. The decreased ksr is due to the reduced electron density at the surface of the semiconductor, resulted predominately from the negatively shifted flat band potential. These findings provide new insights into the mechanism of water photooxidation and enlighten a simple way to develop more efficient electrodes.

An electrochemical quartz crystal microbalance study of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin electropolymerization process

The process of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin electropolymerization has been studied by the quartz crystal microbalance method in different electrodeposition conditions. The films were deposited in two modes: in potentiostatic conditions (at the potential of [Formula: see text]2 V) and in potentiodynamic conditions (CV with the potential scan rate of 20 mV/s). The effect of electrolysis parameters on 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin electropolymerization has been studied by obtaining films in two modes and using two supporting electrolytes: tetrabutylammonium perchlorate or tetrabutylammonium hexafluorophosphate. The biggest film mass gain was observed on a clean electrode surface. At further film deposition on the polyporphyrin-coated electrode, the film mass growth stopped. The electrodeposition effectiveness was somewhat higher in the potentiodynamic conditions, with the formation of a looser film. The nature of the supporting electrolyte did not have a significant effect on the electrodeposition process. A significant contribution to the deposition was made by the electrode material. The film thickness was 25–80 nm. The films possessed [Formula: see text]-type conductivity; and the flat-band potential for poly-H[Formula: see text]T(4-OHPh)P obtained in potentiodynamic conditions was 0.33 V, for poly-H[Formula: see text]T(4-OHPh)P obtained in potentiostatic conditions it was 0.16 V.