Photoelectrochemical (PEC) cell is a meaningful way to fulfil carbon dioxide (CO 2 ) conversion to value-added chemicals, but the exploration of ideal photocathode materials with high photo-conversion efficiency remains a challenge. Herein, porous ZnO@ZnSe core/shell nanosheet array on fluorine doped-tin oxide (FTO) glass is synthesized via dissolution-recrystallization mechanism by using ZnO nanosheet array as the template, and is used for the first time as the photocathode for PEC reduction of CO 2 . The effect of ZnSe loading amount on PEC responses of composite electrode is investigated in detail. Under the irradiation of visible light, the optimized ZnO@ZnSe photocathode exhibits onset potentials at 0.39 V ( vs. RHE) in CO 2 -purged 0.5 M NaHCO 3 solution and achieves the photocurrent of 1.17 mA cm -2 at −0.11 V ( vs. RHE). Interestingly, the competitive H 2 evolution reaction can be suppressed effectively and thereby the selectivity for CO 2 reduction reactions especially for CO formation is increased when the applied voltage became more negative. The faradic efficiency of CO increases dramatically from 4.2% at 0.2 V to 52.9% at −0.4 V and the electron selectivity for CO 2 reduction increases from 70.1% to 96.6% accordingly. These results demonstrate that ZnO@ZnSe composite electrode can work as promising photocathode for efficient CO 2 reduction.
Realizing multicolored luminescence in two-dimensional (2D) nanomaterials would afford potential for a range of next-generation nanoscale optoelectronic devices. Moreover, combining fine structured spectral line emission and detection may further enrich the studies and applications of functional nanomaterials. Herein, a lanthanide doping strategy has been utilized for the synthesis of 2D ZnSe:Er3+ nanosheets to achieve fine-structured, multicolor luminescence spectra. Simultaneous upconversion and downconversion emission is realized, which can cover an ultrabroadband optical range, from ultraviolet through visible to the near-infrared region. By investigating the low-temperature fine structure of emission spectra at 4 K, we have observed an abundance of sublevel electronic energy transitions, elucidating the electronic structure of Er3+ ions in the 2D ZnSe nanosheet. As the temperature is varied, these nanosheets exhibit tunable multicolored luminescence under 980 and 365 nm excitation. Utilizing the distinct sublevel transitions of Er3+ ions, the developed 2D ZnSe:Er3+ optical temperature sensor shows high absolute (15.23% K–1) and relative sensitivity (8.61% K–1), which is superior to conventional Er3+-activated upconversion luminescent nanothermometers. These findings imply that Er3+-doped ZnSe nanomaterials with direct and wide band gap have the potential for applications in future low-dimensional photonic and sensing devices at the 2D limit.
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