摘要
Solar thermochemical CO_(2)-splitting(STCS)is a promising solution for solar energy harvesting and storage.However,practical solar fuel production by utilizing earth-abundant iron/iron oxides remains a great challenge because of the formation of passivation layers,resulting in slow reaction kinetics and limited CO_(2)conversion.Here,we report a novel material consisting of an iron-nickel alloy embedded in a perovskite substrate for intensified CO production via a two-step STCS process.The novel material achieved an unprecedented CO production rate of 381 mL g^(-1)min^(-1)with 99%CO_(2)conversion at 850℃,outperforming state-of-the-art materials.In situ structural analyses and density functional theory calculations show that the alloy/substrate interface is the main active site for CO_(2)splitting.Preferential oxidation of the FeNi alloy at the interface(as opposed to forming an FeO_(x)passivation shell encapsulating bare metallic iron)and rapid stabilization of the iron oxide species by the robust perovskite matrix significantly promoted the conversion of CO_(2)to CO.Facile regeneration of the alloy/perovskite interfaces was realized by isothermal methane reduction with simultaneous production of syngas(H_(2)/CO=2,syngas yield>96%).Overall,the novel perovskite-mediated dealloying-exsolution redox system facilitates highly efficient solar fuel production,with a theoretical solar-to-fuel efficiency of up to 58%,in the absence of any heat integration.
大气中CO_(2)含量的增加已对气候和环境造成巨大影响,要实现碳中和的目标,目前迫切需要开发CO_(2)高效利用技术.太阳能热化学循环CO_(2)裂解可充分利用太阳全光谱能量将CO_(2)转化为CO,从而实现太阳能到化学能的存储.进一步引入CH_(4)作为氧载体的还原气体,不仅能有效降低反应温度、提高氧载体供氧能力,还能联产高质量合成气,为生产甲醇和乙酸及费托合成提供原料,达到一举多得的效果.铁基材料因其成本低、环境友好等优点受到广泛关注,但普通铁氧化物(如Fe_(3)O_(4),FeO)催化甲烷活化性能差,且受热力学限制,CO_(2)分解转化率较低.本文制备了一种FeNi合金修饰的钙钛矿复合材料为氧载体(FeNi-LFA),其在两步法太阳能热化学CO_(2)裂解反应中展现出较好的反应活性和循环稳定性.在反应温度为850℃时,CO_(2)分解速率达到381 mL g^(-1)min^(-1)(STP),转化率达到99%,氧化后材料可在恒温条件下经甲烷还原再生,合成气收率达96%以上,30次循环性能无明显下降.本文还结合高分辨透射电子显微镜(HRTEM),原位X射线衍射(XRD),原位扫描透射电镜(STEM)和57Fe穆斯堡尔谱等表征深入研究了热化学循环反应中氧载体的结构演变,并借助密度泛函理论(DFT)计算,研究其构效关系.HRTEM及EDS结果表明,FeNi-LFA中FeNi合金颗粒尺寸为20~50 nm,且合金颗粒部分嵌入到钙钛矿基体中,从而显著增强了金属-载体间相互作用.为了研究FeNi-LFA氧载体动态构造演化过程,采用XRD对氧载体反应中衍射峰变化进行研究.当FeNi-LFA暴露于CO_(2)中,FeNi合金的特征衍射峰向高角度偏移,同时,La_(2)O_(3)衍射峰减弱.钙钛矿衍射峰增强,说明氧化气氛中,FeNi合金发生Fe脱合金过程,而氧化后的铁离子能与La_(2)O_(3)快速反应生成钙钛矿氧化物.当反应气氛切换成CH_(4)后,钙钛矿衍射峰强度降低,La_(2)O_(3)信号相应增强,说明钙钛矿中铁离子脱溶析
基金
国家自然科学基金(21706254,21676269,21676266,21878283,21978239,22022814)
中国科学院先导专项(XDB17020100)
大连化学物理研究所基金(DICPI201916)
中国科学院科学研究基金(CXJJ-20S034)
国家重点研发项目(2016YFA0202-801).
