The Effect of Mo Doping on The Charge Separation Dynamics and Photocurrent Performance of BiVO\u3csub\u3e4\u3c/sub\u3e Photoanodes

Doping with electron-rich elements in BiVO4 photoanodes has been demonstrated as a desirable approach for improving their carrier mobility and charge separation efficiency. However, the effect of doping and dopant concentration on the carrier dynamics and photoelectrochemical performance remains unclear. In this work, we examined the effects of Mo doping on the charge separation dynamics and photocurrent performance in BiVO4photoanodes. We show that the photocurrent of BiVO4 photoanodes increases with increasing concentration of the Mo dopant, which can be attributed to both the improved carrier mobility resulting from increased electron density and charge separation efficiency due to the diminishing of trap states upon Mo doping. The effect of doping on the electronic structure, carrier dynamics and photocurrent performance of BiVO4 photoanodes resulting from W and Mo dopants was also compared and discussed in this study. The knowledge gained from this work will provide important insights into the optimization of the carrier mobility and charge separation efficiency of BiVO4 photoanodes by controlling the dopants and their concentrations

Photoinduced interfacial charge separation dynamics in zeolitic imidazolate framework

Owing to their porous structure and tunable framework, zeolitic imidazolate frameworks (ZIFs) have garnered considerable attention as promising photocatalytic materials. However, little is known regarding their photophysical properties. In this work, we report the photoinduced charge separation dynamics in a ZIF-67 thin film through interfacial electron transfer (ET) to methylene blue (MB+) via ultrafast transient absorption spectroscopy. We show that the ET process occurs through two distinct pathways, including an ultrafast (\u3c200 fs) process from the [CoII(mim)2] units located on the surface of ZIF-67 film that are directly in contact with MB+ and a relatively slower ET process with a 101.4 ps time constant from the units in the bulk of the film that were isolated from MB+ by the surface units. This first direct evidence of the ET process from ZIF-67 to electron acceptor strongly suggests that ZIF materials may be used as intrinsic photocatalytic materials rather than inert hosts

Implicating the Contributions of Surface and Bulk States on Carrier Trapping and Photocurrent Performance of BiVO\u3csub\u3e4\u3c/sub\u3e Photoanodes

Monoclinic-scheelite BiVO4 has been widely studied as a promising oxygen evolution reaction (OER) catalyst in artificial photosynthesis. Though significant progress to improve or augment its catalysis performance has been made, fundamental understanding of its relatively poor performance as a bare material is lacking. In this paper, we report the correlation of the surface structure and trap states with charge separation efficiency and OER performance of bare BiVO4 photoanodes viavarying the sample thickness. Using X-ray absorption spectroscopy (XAS), we observed a more compacted, symmetric Bi center in the surface state. Using transient absorption (TA) spectroscopy, we show that the structural properties of the surface lead to shallow and deep hole trap states and electron trapping that occurs at the surface of the material. Despite more severe carrier trapping on the surface, our OER measurements demonstrate that a significant bulk structure is required for light absorption but is only beneficial until the carrier mobility becomes the limiting factor in photoelectrochemical cell studies

Exceptionally Long-Lived Charge Separated State in Zeolitic Imidazolate Framework: Implication for Photocatalytic Applications

Zeolitic imidazolate frameworks (ZIFs) have emerged as a novel class of porous metal–organic frameworks (MOFs) for catalysis application because of their exceptional thermal and chemical stability. Inspired by the broad absorption of ZIF-67 in UV–vis-near IR region, we explored its excited state and charge separation dynamics, properties essential for photocatalytic applications, using optical (OTA) and X-ray transient absorption (XTA) spectroscopy. OTA results show that an exceptionally long-lived excited state is formed after photoexcitation. This long-lived excited state was confirmed to be the charge-separated (CS) state with ligand-to-metal charge-transfer character using XTA. The surprisingly long-lived CS state, together with its intrinsic hybrid nature, all point to its potential application in heterogeneous photocatalysis and energy conversion