Showing papers by "Rengui Li published in 2019"

Copper oxide nanowires for efficient photoelectrochemical water splitting

Abstract: Photoelectrochemical (PEC) splitting of water into hydrogen and oxygen by the direct use of sunlight is an ideal, renewable method for solar-to-chemical conversion. Photocathodes based on p-type copper oxide (CuO) are promising materials for large-scale and widespread PEC water splitting due to the abundance of copper element, suitable band gap, and favorable band alignments. In this work, we fabricated one-dimensional CuO nanowires on Cu foils via a facile thermal-treatment process for PEC water splitting. The well-defined CuO nanowire-based photocathodes exhibit an obvious photocurrent responsive character of a p-type semiconductor with onset potential at ∼700 mV vs. RHE. The CuO photocathode shows a photocurrent of ∼1.4 mA cm−2 at 0 V vs. RHE under AM 1.5 G irradiation, which is one of the highest photocurrents based on bare CuO photocathode. Further depositing Pt nanoparticles as cocatalyst on the surface of CuO nanowires to accelerate surface reaction and inhibit charge accumulating at semiconductor/solution interface, resulting in a significant improvement of the stability for photoelectrodes. Our work reports a promising method for fabricating well-defined metal oxides-based photoelectrodes, which providing a promising candidate for highly efficient no bias PEC devices for solar fuels production.

Homophase Junction for Promoting Spatial Charge Separation in Photocatalytic Water Splitting

Abstract: The widespread heterojunction or p–n junction strategies fabricated between different semiconductors are generally used to promote the spatial charge separation in photocatalysis and solar cells, w...

Boosting photocatalytic water splitting by tuning built-in electric field at phase junction

Abstract: Constructing a built-in electric field at the interface of semiconductors has been demonstrated to provide the driving force for spatial charge separation in photocatalysis. Although phase junctions (interfaces formed between two crystalline phases of the same semiconductor) have been demonstrated to be effective in spatial charge separation, regulation of the photocatalytic activity by precisely tuning the built-in electric fields is not yet well understood. In this work, taking anatase/rutile TiO2 phase junction as an example, the built-in electric field in the phase junction region was modulated via fabricating controllable anatase nanoparticles on rutile TiO2 surface to manipulate the interfacial contact area between anatase and rutile phases. We found that photocatalytic H2 evolution depends strongly on the interfacial contact area between anatase and rutile TiO2. The relation between the anatase/rutile phase junction interfacial contact area and the specific photocatalytic activity shows a typical volcano curve, that is, increasing the interfacial contact area results in enhancement of the driving force for spatial charge separation, allowing more electrons and holes to migrate to the surface and participate in redox reactions, but further increasing the interfacial contact area leads to decline of photocatalytic activity. The optimized interfacial contact is the most favorable balance between the strength of built-in electric field and transfer distance for photogenerated charge carriers for separation and transfer of photo-generated electrons and holes at the phase junction region. Our work provides new insight into the construction of built-in electric fields on the surface of semiconductor-based photocatalysts to boost spatial charge separation for solar energy conversion systems.

Novel conjugated organic polymers as candidates for visible-light-driven photocatalytic hydrogen production

Abstract: Artificial photosynthesis aiming to capture and convert renewable solar energy into solar fuels (eg, hydrogen, chemicals) provides a blueprint for sustainable and carbon-neutral world In artificial photosynthesis, developing novel semiconductors for visible-light-driven photocatalytic water splitting is one of the most demanding challenges Herein, we designed and explored two kinds of novel bipyridine-based covalent organic polymers, Bp-COP (2,2′-bipyridine-5,5′-diamine: Bp-NH2) and BpZn-COP (2,2′-bipyridine-5,5′-diamine Zn complex: Bp-Zn), both of which exhibit excellent light-harvesting properties with absorption edges expanding to larger than 600 nm and have appropriate band structures for water splitting Polymers Bp-COP and BpZn-COP are found to enable efficient photocatalytic hydrogen production under visible light irradiation with Pt as the proton reduction cocatalyst Further assembling conjugated organic polymers with TiO2 as charge transferring mediate can remarkably boost their photocatalytic activities to more than 8 times (1333 vs 162 μmol g−1 h−1), giving an apparent quantum efficiency (AQE) of over 25% at the input wavelength of 420 nm This work not only presents a methodology for designing and synthesizing novel organic-based polymers, but also provides promising candidates for potential applications in solar energy conversion

In-situ fabrication of atomic charge transferring path for constructing heterojunction photocatalysts with hierarchical structure

Abstract: The efficiencies of photocatalytic solar energy conversion systems are significantly limited by the challenging charge separation process, which can be improved via some commonly-used interfacial modulating strategies, e.g., introducing heterojunctions at the interfaces of different semiconductors. However, in many cases, the constructed heterojunctions not always work well mainly due to the serious mismatching of surface and energy structures between different components. In this study, inspired by the similarities in crystalline structures and elemental compositions, a novel heterojunction photocatalyst with hierarchical structure was first fabricated between bismuth-based semiconductors (Bi2Ti2O2 and gamma-Bi2O3) possessing identical cubic phase via a simple insitu transformation method. The resulted Bi2Ti2O7/gamma-Bi2O3 heterojunction photocatalyst (denoted as BT/gamma-Bi2O3) shows extremely high photocatalytic activities in photocatalytic removal of various high concentration environmental pollutants, e.g., phenol, dyes and sulfur containing compounds. An enhancement of more than two orders of magnitude in photocatalytic performances can be achieved for the BT/gamma-Bi2O3 photocatalyst than the single composite, which is possibly attributable to the co-sharing of Bi-O tetrahedra units for the composites in heterojunction structures to provide an atomic charge transferring pathway for facilitating the spatial charge separation. This work provides an effective strategy for rationally constructing charge separation and transfer pathway in semiconductor-based photocatalysts for solar energy conversion.

Spatial separation of dual-cocatalysts on one-dimensional semiconductors for photocatalytic hydrogen production

Abstract: Light-driven hydrogen production using semiconductor photocatalysts has gained much interest owing to their ability to store sunlight in the form of portable chemical fuel. The spatial separation of dual-cocatalysts onto different surfaces has been considered as a useful strategy for fabricating dynamic particulate photocatalysts to hinder charge recombination and reverse reactions. Herein, using one-dimensional (1D) semiconductors, CdSe nanorods as an example, we experimentally demonstrated that photogenerated electrons and holes can be effectively separated along different directions of a 1D semiconductor. Following this phenomenon, the reduction cocatalyst Pt and oxidation cocatalyst PdS were spatially deposited on different sites via an in situ photodeposition process, which drastically enhanced the photocatalytic activity for hydrogen production to more than 20 times, thus exhibiting an extremely high apparent quantum efficiency (AQE) of ∼45% at 420 nm. Further studies using photoluminescence spectroscopy indicated that the spatially separated dual-cocatalysts efficiently captured the photogenerated electrons and holes migrating to the surface, which greatly decreased the recombination of charge carriers and consequently led to superior photocatalytic performances. Our work provides an effective strategy for the rational construction of highly efficient photocatalyst systems based on (quasi) 1D semiconductors for artificial solar energy conversion.

Graphene Dispersed Bi2WO6 Nanosheets with Promoted Interfacial Charge Separation for Visible Light Photocatalysis

Abstract: Promoting photogenerated charge separation is the key and bottleneck step in photocatalysis, which mainly determines the efficiency of solar energy conversion. Reduced graphene oxide (rGO) has been emerging in the fields of physics, catalysis and material sciences due to its unique structures, high catalytic activity and tunability. In this work, we introduced rGO nanosheets as support to fabricate uniformly‐dispersed Bi2WO6 nanostructures onto the rGO surface under hydrothermal condition. The resulted rGO/Bi2WO6 composite exhibited superior performances in degradation of various kinds of environmental pollutants including dyes and phenol. Further electrochemical characterizations including open circuit potential, electrochemical impedance spectroscopy and electrochemical specific area indicated that incorporation of rGO evidently accelerated the interfacial charge separation and transfer. These improvements consequently contributed to largely exposed active sites and superior photocatalytic performance. Our work presented a facile strategy to tune the interfacial charge separation in semiconductor‐based photocatalysts using layered materials like graphene and its derivatives.