利用可再生电力将二氧化碳转化为高附加值产品的电催化二氧化碳还原反应(CO2RR)是一项具有革命性潜力的技术,因而备受关注.其中,一氧化碳被视为CO2RR中最具经济效益的产物之一,可直接利用费托合成工艺将其用于合成醛、酮、烃类等产品.酞菁钴(CoPc)作为单位点催化剂,因其高原子利用率和高催化选择性能,在二氧化碳转化为一氧化碳过程中具有很大优势.然而,CoPc无法为CO2RR中的质子化过程提供足够质子,导致其在工业大电流密度下的效率较低.因此,探索一种能够解决CO2RR中质子供给不足问题的高效电催化剂对于提升CO2RR的性能至关重要.本文设计了具有增强质子供给作用的缺陷碳纳米管(d-CNT),将其作为导电载体分散CoPc,用于制备CoPc/d-CNT电催化剂.通过引入富缺陷的碳纳米管(d-CNT),加速水解离进而增加CO2RR的质子供给量.X射线光电子能谱、X射线吸收近边光谱和扩展X射线吸收精细结构谱结果表明,CoPc/d-CNT成功合成,同时保留了CoPc完整的Co-N4配位结构.透射电镜、粉末X射线衍射谱和拉曼光谱共同表明,d-CNT表面缺陷相对于商用CNT明显增加.动力学实验和原位衰减全反射表面增强红外吸收光谱研究表明,含大量缺陷的d-CNT具有加速水解离的能力,显著提高了二氧化碳还原反应过程中的质子供给,从而促进了CoPc上CO2活化生成*COOH.同时,密度泛函理论计算结果表明,d-CNT表面缺陷位点上从吸附水(*H2O)到质子水(H3O+)的吉布斯自由能为0.74 eV,远低于CNT(超过2 eV),表明d-CNT促进了水解过程和质子传递,再次证实了d-CNT降低了水分子解离的势垒.通过实验和理论的共同验证,阐明了d-CNT中的缺陷能够促进水解离,改善CO2RR反应过程中质子供给,增强CoPc高效催化CO2RR的能力.因此,CoPc/d-CNT混合材料表现出较好的催化性能.在电流密度为500 mA cm-2的流动电池中,CoPc/d-CNT的CO法拉第效率(FECO)高达96％.相对而言,CoPc/CNT在200 mA cm-2时FECO已经下降到90％以下.此外,在150 mA cm-2的电流密度下,CoPc/d-CNT能够在20 h内维持FECO超过90％.综上,本文通过引入具有水解离能力的缺陷碳位点,解决了单位点催化剂CoPc在CO2RR中质子供给不足的问题,为设计高性能催化剂提供了新见解.
Proton feeding from defect-rich carbon support to cobalt phthalocyanine for efficient CO2 electroreduction
Electrocatalytic CO2 reduction reaction (CO2RR) holds significant promise for sustainable energy conversion,with cobalt phthalocyanine (CoPc) emerging as a notable catalyst due to its high CO selectivity.However,CoPc's efficacy is hindered by its limited ability to provide sufficient proton for the protonation process,particularly at industrial current densities.Herein,we introduce de-fect-engineered carbon nanotubes (d-CNT) to augment proton feeding for CO2RR over CoPc,achieved by expediting water dissociation.Our kinetic measurements and in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy reveal d-CNT significantly enhances proton feeding,thereby facilitating CO2 activation to *COOH in CoPc.Density functional theory cal-culations corroborate these findings,illustrating that d-CNT decreases the barrier to water dissocia-tion.Consequently,the CoPc/d-CNT mixture demonstrates robust performance,achieving 500 mA cm-2 for CO2RR with CO selectivity exceeding 96％.Notably,CoPc/d-CNT remains stability for a duration of 20 h under a substantial current density of 150 mA cm-2.The study broadens the scope of practical applications for molecular catalysts in CO2RR,marking a significant step towards sus-tainable energy conversion.
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