摘要
Pyridinic N is widely regarded as the active center while pyrrolic N has low‐activity in metal‐free N‐doped carbon for electrocatalytic CO_(2) reduction reaction(CO_(2)RR)to CO,but this viewpoint remains open to question.In this study,through density functional theoretical calculations,we first illustrate that the intrinsic activity of pyrrolic N is high enough for effectively catalyzing CO_(2)RR,however,due to the interplay with the neighboring pyridinic N sites,the activity of pyrrolic N is dramatically suppressed.Then,experimentally,metal‐free N‐doped carbon spheres(NCS)electrocatalysts without significant pyridinic N content are prepared for CO_(2)RR.The pyrrolic N in NCS shows a direct‐positive correlation with the performance for CO_(2)RR,representing the active center with high activity.The optimum NCS could produce syngas with a wide range of CO/H_(2) ratio(0.09 to 12)in CO_(2)RR depending on the applied potential,meanwhile,the best selectivity of 71%for CO can be obtained.Intentionally adding a small amount of pyridinic N to the optimum NCS dramatically decreases the activity for CO_(2)RR,further verifying the suppressed activity of pyrrolic N sites by the neighboring pyridinic N sites.This work reveals the interaction between a variety of N species in N‐doped carbon,and the potential of pyrrolic N as the new type of active site for electrocatalysts,which can improve our understanding of the electrocatalysis mechanism and be helpful for the rational design of high‐efficient electrocatalysts.
随着化石燃料的过度燃烧以及污染的持续加剧,诸如海水酸化和气候变暖等问题逐渐显现,因此人们开始日益关注大气中CO_(2)的浓度.近些年,由于碳基材料具有成本低、化学和机械稳定性良好、电导率高和有效抑制析氢反应等优点而被广泛用于CO_(2)还原反应(CO_(2)RR).杂原子(B, P和N)掺杂可以有效地改变碳基材料电子结构并提高CO_(2)RR的选择性和活性.其中,由于氮原子具有独特的优势而被作为碳基材料的掺杂元素.在无金属氮掺杂碳材料中,吡啶氮被广泛地认为是催化活性中心,而吡咯氮则被认为不具催化活性,该观点仍存在争议.本文首先通过密度泛函理论计算证明了吡咯氮的本征活性足以有效催化CO_(2)RR,但由于与相邻吡啶氮位点的相互作用,吡咯氮的活性被显著抑制.此外,进一步通过实验制备了不含吡啶氮的无金属氮掺杂碳球(NCS)作为CO_(2)RR电催化剂.NCS中的吡咯氮与CO_(2)RR的性能呈直接正相关,表明其可以成为活性中心.性能最佳的NCS可在CO_(2)RR中产生范围较宽的合成气(CO/H_(2)(0.09-12)), CO选择性最高可达71%.在最优NCS中加入少量吡啶氮显著降低了CO_(2)RR的活性,进一步验证了相邻吡啶氮位点对吡咯氮活性的抑制作用.综上,本工作揭示了各种氮物种之间的交互作用,以及吡咯氮可以作CO_(2)RR活性位点的潜力;进一步提高了我们对电催化作用机制的理解,有助于高效电催化剂的设计和合成.
基金
国家自然科学基金(51772234,22088102)
大连理工大学中央高校基本科研业务费专项资金资助(DUT19RC(3)063)
中国辽宁省自然科学基金(2021-MS-126)
中国辽宁省生物基化学品重点实验室.
