类空气浓度的二氧化碳的高效电还原

近十年来,电化学转化二氧化碳受到越来越多的关注和研究,其最终目标是利用可再生能源得到电能来实现碳中和,以及经济和能源效益.为实现这一目标,电还原二氧化碳不仅需要较高的选择性和转化率,也需要考虑其大规模应用的成本和经济价值.尽管近年空气中二氧化碳的浓度达到了历史最高值(415 ppm),但仍仅占了空气气体中较少的一部分.从空气中捕获和浓缩二氧化碳需要耗费大量的能量(~8.65 GJ/t),这不可避免地增加了工业成本和复杂性.另外在更负电位的二氧化碳还原反应下存在氧气(O_(2))还原竞争反应,也为二氧化碳电还原带来更大的挑战.因此,目前几乎所有研究报道的二氧化碳电还原体系都是使用高浓度(通常是纯的)二氧化碳作为反应物,只有少数几篇近期文献研究了低浓度二氧化碳(如~10%二氧化碳浓度的烟道气)的电还原性能.此外,在二氧化碳电还原中,中性或者碱性溶液常被用来作为电解液,而气体扩散电极通常用来提高二氧化碳的传质,但在这样的条件下,一部分二氧化碳不可避免地会与碱性或中性的电解液反应或者被吸收,大大降低还原效率.本文设计了一种气相电化学电解槽,并使用低成本的铜或纳米铜催化剂,实现电还原浓度为0.03%或0.04%的二氧化碳.在此过程中,气相二氧化碳与水蒸气混合并直接传递到铜催化剂表面,在气-固界面上被还原为一氧化碳,且在反应过程中二氧化碳不会被水溶液或碱性电解质吸收或发生反应.通过对催化剂和实验参数的调整,当反应气体为0.03%的二氧化碳,在气体流速为0.5 mL/min的条件下,二氧化碳的转化效率可高达95%.此外,本文还成功实现了直接电还原空气中的二氧化碳(0.04%的二氧化碳),由于铜催化剂的氧气还原活性极差,空气中较高浓度的氧气并不会对二氧化碳还原产生较大影响.因此,在空气流速为0.5 mL/min的条件下,二氧化碳的最佳转化效率可达~79%.综上,本文为直接电还原转化二氧化碳提供了具有较好发展前景的方法.

通过双活化策略在Ag-CeO_(2)电催化剂上用苯乙酮高效固定CO_(2)

二氧化碳(CO_(2))是一种主要的温室气体,对全球气候变化和生态环境造成了很大影响.同时,CO_(2)也是一种无毒、廉价、丰富的C_(1)资源,可用于合成用作燃料和药物的各种有机化合物.因此,模拟植物光合作用对CO_(2)进行固定成为了众多科研工作者的研究热点.电化学羧化是将CO_(2)固定在有机分子上的一种有效方法,并且已被证明可以通过构建新的C–C键,使CO_(2)与各种底物(包括酮、二烯和类卤化物等)发生电羧化反应,形成羧酸化合物.然而,由于CO_(2)分子本身的热力学和动力学惰性,使得CO_(2)分子的活化颇具挑战性,难以实现高效转化.目前,许多研究致力于开发各种用于CO_(2)转化的反应模型和催化剂.例如,结合单个CO_(2)分子形成不同羧酸的单羧基化反应.酮类化合物与CO_(2)的电羧化反应是实现CO_(2)固定并合成羧酸的一种有效途径,得到的羧酸产物可作为许多生物活性化合物的来源.然而,在CO_(2)和芳香酮的电羧化反应中,由于二者的活化具有较大的过电位差异,会严重阻碍电羧化反应的效率并导致产物收率较低.研究表明可以通过同时激活CO_(2)分子和有机底物以促进目标羧化产物的形成.该策略为改善CO_(2)和芳族酮之间的电羧化反应效率提供了思路.本文合成了一种Ag掺杂的CeO_(2)纳米线(Ag-CeO_(2)NWs)作为催化苯乙酮和CO_(2)进行电羧化反应的催化剂.该催化剂能够起到同时活化CO_(2)和苯乙酮分子的作用,实现双重活化的目的.在双重活化策略下,苯乙酮与CO_(2)的电羧化反应可以通过将CO_(2)活化为CO_(2)^(•−),然后通过自由基的形式加成到苯乙酮的双键上;或者,苯乙酮分子被活化成苯乙酮自由基阴离子,苯乙酮自由基阴离子通过亲核反应与CO_(2)偶联,最终形成羧酸产物.与银箔、银纳米颗粒和CeO_(2)纳米线相比,Ag-CeO_(2)纳米线催化剂可以有效降低CO_(2)和苯乙酮分子活化之间的起始电位差,从而能够有效地电羧化形成2-苯乳酸.在-1.8 V vs.Ag/AgI电位下,生成2-苯乳酸的法拉第效率高达91%,收率为83.2%.综上,本文同时激活CO_(2)和有机底物分子的双重活化策略有利于指导催化剂的设计,从而提高CO_(2)固定效率,进而提高电羧化反应的活性和选择性.

Developing silicon-based photocathodes for CO_(2)conversion

Photoelectrochemical(PEC)conversion of CO_(2)presents a promising avenue for solar-driven chemical fuel production,with silicon emerging as a cost-effective and high-light-absorbing material pivotal to this technology.Aiming at exploring opportunities for industrializing PEC CO_(2)reduction(PEC-CO_(2)R)by minimizing reaction energy consumption,enhancing reaction efficiency and selectivity,this review summarizes recent advancements in developing Si-based photocathodes for PEC-CO_(2)R.It outlines the fundamental principles,advantages,and limitations of Si photocathodes with key performance metrics.Based on this understanding,the strategies to enhance the performance of the PEC-CO_(2)R system,including light absorption,charge separation,and catalytic reactions are categorized as the interfacial modification,active site decoration,and protective layer design.The design ideas of this advantageous three-layer structure in promoting the efficiency,stability,and selectivity have been clarified.Then,this review scrutinizes the influence of the photocathodic chemical environment.This review consolidates the mechanism insights and notable breakthroughs of various fuel generation processes within Si-based PEC-CO_(2)R systems.Providing this wealth of information offers an up-to-date perspective on the dynamic developments in silicon-based PEC-CO_(2)conversion and underscores the promising pathways toward the sustainable fuel synthesis from pollutant CO_(2).

Solution chemistry quasi-epitaxial growth of atomic CaTiO_(3)perovskite layers to stabilize and passivate TiO_(2)photoelectrodes for efficient water splitting

Perovskite oxides with unique crystal structures and high defect tolerance are promising as atomic surface passivation layers for photoelectrodes for efficient and stable water splitting.However,controllably depositing and crystalizing perovskite-type metal oxides at the atomic level remains challenging,as they usually crystalize at higher temperatures than regular metal oxides.Here,we report a mild solution chemistry approach for the quasi-epitaxial growth of an atomic CaTiO_(3)perovskite layer on rutile TiO_(2)nanorod arrays.The high-temperature crystallization of CaTiO_(3)perovskite is overcome by a sequential hydrothermal conversion of the atomic amorphous TiOx layer to CaTiO_(3)perovskite.The atomic quasi-epitaxial CaTiO_(3)layer passivated TiO_(2)nanorod arrays exhibit more efficient interface charge transfer and high photoelectrochemical performance for water splitting.Such a mild solution-based approach for the quasi-epitaxial growth of atomic metal oxide perovskite layers could be a promising strategy for both fabricating atomic perovskite layers and improving their photoelectrochemical properties.

Photodeposited FeOOH vs electrodeposited Co-Pi to enhance nanoporous BiVO4 for photoelectrochemical water splitting

Co-Pi and FeOOH cocatalysts were in-situ deposited on the surface of nanoporous BiVO4 photoelectrodes.The FeOOH cocatalyst has little effect on the BiVO4 samples＇ morphologies,while the electrodeposited CoPi cocatalyst seems to affect the surface of BiVO4 The impedance intensity modulated photocurrent spectroscopy（IMPS）,Mott-Schottky（M-S） techniques characterize BiVO4 samples photoelectrochemical performance with the deposition of Co-Pi and FeOOH.The Co-Pi/BiVO4 shows better photoelectrochemical performance than the FeOOH/BiVO4,but the FeOOH/BiVO4 exhibited the better stabilities.The flat band potential and slope of M-S plotof FeOOH/BiVO4 have little variations compared with BiVO4.In contrast,Co-Pi/BiVO4 exhibited the down shifted flat band potential,which is beneficial for the photoelectrochemical water oxidation.The electron transfer measurements revealed that the deposition of FeOOH and Co-Pi onto BiVO4 significantly enhanced the photoelectrochemical performance via reducing the interface resistance and promoting the electron transport.Furthermore,Co-Pi cocatalysts can further pin the transport-limiting traps and significantly facilitate the electron transport.

MA Cation-Induced Diffusional Growth of Low-Bandgap FA-Cs Perovskites Driven by Natural Gradient Annealing

Low-bandgap formamidinium-cesium(FA-Cs)perovskites of FA_(1-x)CsxPbI_(3)(x<0:1)are promising candidates for efficient and robust perovskite solar cells,but their black-phase crystallization is very sensitive to annealing temperature.Unfortunately,the low heat conductivity of the glass substrate builds up a temperature gradient within from bottom to top and makes the initial annealing temperature of the perovskite film lower than the black-phase crystallization point(~150℃).Herein,we take advantage of such temperature gradient for the diffusional growth of high-quality FA-Cs perovskites by introducing a thermally unstable MA^(+)cation,which would firstly formα-phase FA-MA-Cs mixed perovskites with low formation energy at the hot bottom of the perovskite films in the early annealing stage.The natural gradient annealing temperature and the thermally unstable MA^(+)cation then lead to the bottom-to-top diffusional growth of highly orientatedα-phase FA-Cs perovskite,which exhibits 10-fold of enhanced crystallinity and reduced trap density(~3:85×10^(15) cm^(−3)).Eventually,such FA-Cs perovskite films were fabricated into stable solar cell devices with champion efficiency up to 23.11%,among the highest efficiency of MA-free perovskite solar cells.

揭示和调控二氧化碳电还原中甲烷与二碳产物的线性关系

尽管许多催化剂已经被报道用于电化学转换二氧化碳(CO_(2))到甲烷(CH_(4))或者二碳(C_(2))产物,然而目前对各种产物之间的关联的研究仍然不够深入,这阻碍着催化剂设计的进一步发展.本文通过研究商品化铜粉(Cu)作为CO_(2)电还原的阴极催化剂,发现一氧化碳中间体(*CO)在催化剂表面的覆盖度在较大的电位区间内会保持基本不变,且在这个电位区间内,CH_(4)与C_(2)产物的分电流密度呈线性关系,这一结论得到了理论动力学分析的支持.由于*CHO中间体分子是产生CH_(4)(*CHO→CH_(4))与C_(2)产物(*CHO+*CO→C_(2))的共同中间体,我们进一步猜想该线性关系是普遍存在的,且可以通过调节催化剂表面的吸附氢(*H)或者一氧化碳(*CO)的覆盖度,以分别促进CH_(4)或者C_(2)产物的生成,并改变线性关系的斜率.为了验证该猜想,本文合成了碳包覆的铜(Cu@C)催化剂,其中碳层可增加催化剂表面的*H覆盖度从而提高CH_(4)的产生,最高的CH_(4)法拉第效率(FE_(CH_(4)))达到52%,相应的分电流密度为±337 m A cm±2.另一方面,合成了银掺杂的铜催化剂,其中掺杂的银用以产生CO,以进一步提高催化剂表面的*CO覆盖度.该催化剂二氧化碳电还原的选择性变成了C_(2)产物为主,最高C_(2)产物的法拉第效率(FE_(CH_(4)))达到79%,相应的分电流密度为±421 m A cm±2.不仅如此,在这两种催化剂上,CH_(4)与C_(2)产物的分电流密度仍然保持良好的线性关系.本文工作揭示了CH_(4)与C_(2)产物产率的线性关系,以及反应中间分子的调控策略,为电催化二氧化碳还原为不同的产物提供了参考.