ABSTRACT
Various electrocatalysts are extensively examined for their ability to selectively produce desired products by electrochemical CO2 reduction reaction (CO2RR). However, an efficient CO2RR electrocatalyst doesn't ensure an effective co-catalyst on the semiconductor surface for photoelectrochemical CO2RR. Herein, Bi2S3 nanorods are synthesized and electrochemically reduced to Bi nanoplates that adhere to the substrates for application in the electrochemical and photoelectrochemical CO2RR. Compared with commercial-Bi, the Bi2S3-derived Bi (S-Bi) nanoplates on carbon paper exhibit superior electrocatalytic activity and selectivity for formate (HCOO-) in the electrochemical CO2RR, achieving a Faradaic efficiency exceeding 93%, with minimal H2 production over a wide potential range. This highly selective S-Bi catalyst is being employed on the Si photocathode to investigate the behavior of electrocatalysts during photoelectrochemical CO2RR. The strong adhesion of the S-Bi nanoplates to the Si nanowire substrate and their unique catalytic properties afford exceptional activity and selectivity for HCOO- under simulated solar irradiation. The selectivity observed in electrochemical CO2RR using the S-Bi catalyst correlates with that seen in the photoelectrochemical CO2RR system. Combined pulsed potential methods and theoretical analyses reveal stabilization of the OCHO* intermediate on the S-Bi catalyst under specific conditions, which is critical for developing efficient catalysts for CO2-to-HCOO- conversion.
ABSTRACT
Electrochemical carbon dioxide reduction is a mild and eco-friendly approach for CO2 mitigation and producing value-added products. For selective electrochemical CO2 reduction, single-crystalline Au particles (octahedron, truncated-octahedron, and sphere) are synthesized by consecutive growth and chemical etching using a polydiallyldimethylammonium chloride (polyDDA) surfactant, and are surface-functionalized. Monodisperse, single-crystalline Au nanoparticles provide an ideal platform for evaluating the Au surface as a CO2 reduction catalyst. The polyDDA-Au cathode affords high catalytic activity for CO production, with >90% Faradaic efficiency over a wide potential range between -0.4 and -1.0 V versus RHE, along with high durability owing to the consecutive interaction between dimethylammonium and chloride on the Au surface. The influence of polyDDA on the Au particles, and the origins of the enhanced selectivity and stability are fully investigated using theoretical studies. Chemically adsorbed polyDDA is consecutively affected the initial adsorption of CO2 and the stability of the *CO2 , *COOH, and *CO intermediates during continuous CO2 reduction reaction. The polyDDA functionalization is extended to improving the CO Faradaic efficiency of other metal catalysts such as Ag and Zn, indicating its broad applicability for CO2 reduction.
ABSTRACT
A BiVO4/Bi2S3 composite comprising Bi2S3 nanowires on top of a BiVO4 film was prepared via hydrothermal reaction. Because additional Bi3+ ions were not delivered during the reaction, BiVO4 served as the Bi3+ ion source for the development of Bi2S3. A detailed growth mechanism of the nanowire was elucidated by an analysis of the concentration gradient of Bi3+ and S2- ions during the reaction. The in situ growth was followed by the etching of BiVO4 to Bi3+ and VO43- ions and regrowth to Bi2S3, which resulted in the rapid evolution of nanowires on the BiVO4 substrate. The fabricated BiVO4/Bi2S3NW composite exhibited an improved photoelectrochemical activity compared to other Bi2S3 samples. The improved efficiency was mainly attributed to both improved charge separation and effective adhesion obtained by the in situ growth.
ABSTRACT
In this study, the reaction mechanisms of metal-semiconductor composites used as photocatalysts were demonstrated by first preparing bismuth vanadate (BiVO4) and then performing photodeposition of metal nanoparticles. The photocatalytic activity of metal-BiVO4 (M-BiVO4, where M = Pt, Au, Ag) composites were evaluated through dye decomposition under UV-vis irradiation. The photocatalytic efficiency was significantly enhanced after Pt deposition as compared to other M-BiVO4 composites. The size or shape of BiVO4 was not the main factor for the efficiency of Pt-BiVO4. However, a deposited Pt co-catalyst was essential for the photocatalytic decomposition of dye on the BiVO4 surface. Radical scavengers were employed to elucidate the reaction mechanism during the photocatalytic reaction with the Pt-BiVO4 composite. This study provides details on the reaction mechanism of the photocatalytic reaction on Pt at the BiVO4 surface under solar irradiation.
ABSTRACT
A single-crystalline Bi2S3 nanowire array (Bi2S3NWA) is synthesized by an in situ hydrothermal reaction on the surface of a Bi2MoO6 film. As no additional source of Bi3+ is provided during the process, the Bi2MoO6 layer acts as the Bi3+ source for the synthesis of Bi2S3 nanowires. The fabricated Bi2MoO6/Bi2S3NWA electrode exhibited an increased photoelectrochemical (PEC) sulfite oxidation activity, which is attributed mainly to the effective interface obtained by the in situ hydrothermal growth, compared to other Bi2S3 electrodes. The generated electron from the Bi2S3 conduction band rapidly transfers to that of Bi2MoO6, yielding an enhanced electron separation of Bi2S3. Furthermore, the single-crystalline Bi2S3 nanowire can provide a fast electron pathway to Bi2MoO6 through its single domain, which also contributes to the improved PEC activity.
ABSTRACT
A pinhole-free BiVO4 electrode was successfully synthesized using an ultrasonic-assisted synthetic method on a conductive substrate. The pinhole-free BiVO4 electrode showed highly improved photoelectrochemical activity for both sulfite oxidation and water oxidation. The blocking recombination processes were examined to clarify the enhanced photoelectrochemical performances.
