0428同步年報-2021-全

Chemical Science 023 In summary, the design of the atomically precise photocatalyst represents a prospective strategy to regulate the capability of catalyst dehydrogenation and to control the path of CH 4 conversion. The ability to resolve fine structures of atomically dispersed metal sites makes synchrotron-based XAFS spectroscopy an important technique to unravel the relations between catalyst structure and performance. (Reported by Chih-Wen Pao) This report features the work of Yujie Xiong and his collaborators published in J. Am. Chem. Soc. 143 , 269 (2021). TPS 44A Quick-scanning X-ray Absorption Spectroscopy • XAS, Time-resolved XAS, XAFS, μXFM • Physics, Chemistry, Catalysis and Surface Science, Materials Science, Biology, Environmental Science Reference 1. W. Jiang, J. Low, K. Mao, D. Duan, S. Chen, W. Liu, C.-W. Pao, J. Ma, S. Sang, C. Shu, X. Zhan, Z. Qi, H. Zhang, Z. Liu, X. Wu, R. Long, L. Song, Y. Xiong, J. Am. Chem. Soc. 143 , 269 (2021). Unraveling the Cathode Chemistry of the Li-Battery Using Ambient-Pressure X-ray Photoelectron Spectra Ambient-pressure X-ray photoelectron spectra showed that H 2 O in a reaction mixture activated Li-CO 2 in the battery discharge, producing unrecyclable carbonate. Conversely, O 2 jumpstarted battery discharging while building recyclable amorphous carbon along with Li 2 O 2 and Li 2 O. R echargeable Li-CO 2 batteries have attracted intense research attention for their potential as energy storage and CO 2 fixation. Since the first demonstration of the prototypical design in 2013, cycle performance has been improved substantially, but further progress became sluggish due to a shortage of fundamental understanding. Several studies showed that Li-CO 2 obtains a moderate capacity during discharging in pure CO 2 . Based thereon, it was suggested that the cathode undergoes a CO 2 -to-C transformation, denoted as a CO 2 reduction reaction (CRR). Other studies showed, however, that the discharge capacity is negligible in pure CO 2 and requires O 2 at a particular proportion to accelerate the reaction. This discrepancy in the CRR kinetic and reaction mechanism remains elusive. Yi-Chun Lu (Chinese University of Hong Kong, China) collaborated with Chia-Hsin Wang and Yaw-Wen Yang (NSRRC), to study Li-CO 2 batteries using ambient-pressure X-ray photoelectron spectra (APXPS), a technique that has become a standard means for studies in situ over the past two decades. The APXPS system in the NSRRC is currently setup at the beamline TLS 24A1 for user operation. Thanks to the turbo pumping to the experimental vacuum vessel, this technique operates at a baseline pressure less than 10 -7 mbar. This condition allows a well controlled operating environment to be created for the battery system. Taking advantage thereof, the authors studied the composition of the cathode surface during charging and discharging of an ionic-liquid-based Li-CO 2 battery; its structure is illustrated in Fig. 1 . Under 5 mbar of pure CO 2 , the authors found that the discharge current consisted solely of a non-faradaic double-layer charging, a conclusion based on the evolution of the ionic liquid electrolyte XPS. In parallel, no sign of carbonate or other new species was observed in the C 1s spectra of all discharging potential, indicating that Li-CRR is electrochemically inactive in pure CO 2 . Fig. 2 : Schematic illustration of photocatalytic conversion of CH 4 to C 2 H 4 through surface alkoxy intermediates over a ZnO-AuPd hybrid. [Reproduced from Ref. 1]