Improved nitrogen reduction electroactivity by unique MoS_(2)‐SnS_(2) heterogeneous nanoplates supported on poly(zwitterionic liquids)functionalized polypyrrole/graphene oxide

基于聚(两性离子液体)功能化聚吡咯/氧化石墨烯的独特MoS_(2)-SnS_(2)异质纳米片及其改善的氮还原电活性

Unique MoS_(2)‐SnS_(2)heterogeneous nanoplates have successfully in‐situ grown on poly(3‐(1‐vinylimidazolium‐3‐yl)propane‐1‐sulfonate)functionalized polypyrrole/graphene oxide(PVIPS/PPy/GO).PVIPS can attract heptamolybdate ion(Mo7O246−)and Sn^(4+)as the precursors by the ion‐exchange,resulting in the simultaneous growth of 1T’‐MoS2 and the berndtite‐2T‐type hexagonal SnS_(2)by the interfacial induced effect of PVIPS.The obtained MoS_(2)‐SnS_(2)/PVIPS/PPy/GO can serve as electrocatalysts,exhibiting good NRR performance by the synergistic effect.The semi‐conducting SnS_(2)would limit the surface electron accessibility for suppressing HER process of 1T’‐MoS_(2),while metallic 1T’‐MoS_(2)might efficiently improve the NRR electroactivity of SnS_(2)by the creation of Mo‐Sn‐Sn trimer catalytic sites.Otherwise,the irreversible crystal phase transition has taken place during the NRR process.Partial 1T’‐MoS_(2)and SnS_(2)have electrochemically reacted with N_(2),and irreversibly converted into Mo^(2)N and SnxNz due to the formation of Mo−N and Sn−N bonding,meanwhile,partial SnS_(2) has been irreversibly evolved into SnS due to the reduction by the power source in the electrochemical system.It would put forward a new design idea for optimizing the preparation method and electrocatalytic activity of transition metal dichalcogenides.

NH_(3)是一种重要的化工原料,广泛应用于合成各种化工产品.然而,传统还原N_(2)制备NH_(3)的Haber-Bosch工艺执行条件苛刻,在消耗大量化石能源的同时产生严重环境污染.在环境条件下的电化学氮还原反应(NRR)是一种最具前景的可持续、清洁生产NH_(3)的能源技术,其实际应用的核心是开发高效、价格低廉和易制备的NRR电催化剂.过渡金属二硫族化合物(TMDCs)储量丰富并且价格低廉,具有多变的晶体结构和相组成、可控的形貌、缺陷设计可调节等特点,呈现出优异的电催化活性,是用来替代贵金属的理想选择.MoS_(2)和SnS_(2)都可作为电催化剂应用于NRR.由于金属1T-MoS_(2)和1T’-MoS_(2)对与NRR竞争的析氢反应(HER)具有极好的电化学活性,其NRR法拉第效率较低;尽管具有半导体特性的SnS_(2)能够通过限制表面电子可及性来抑制HER,但是高过电位和较低氨产率仍不能令人满意.据报道,在碳布上原位生长Mo掺杂SnS_(2)具有丰富的S空位,由于杂原子掺杂和空位工程形成了Mo-Sn-Sn三元催化位点,其NRR活性显著增强.因此,为了抑制竞争反应以提高NRR的法拉第效率,本文设计并制备了一种独特的无机/有机分级纳米结构用于电催化NRR.选用一种独特的聚两性离子液体,即侧链同时含有咪唑盐和磺酸基团的聚1-乙烯基-3-丙烷磺酸基咪唑盐(PVIPS),作为界面诱导剂,利用离子交换作用吸附作为前驱体的Mo7O246‒和Sn^(4+),诱导1T’-MoS_(2)和2T型六方SnS_(2)同时生长,形成独特的MoS_(2)-SnS_(2)异质纳米片负载于PVIPS功能化的聚吡咯/氧化石墨烯(PVIPS/PPy/GO)表面.由于各组分的协同效应,得到的MoS_(2)-SnS_(2)/PVIPS/PPy/GO纳米片表现出较好的NRR活性,其在‒0.5 V(vs.RHE)时氨产率最佳,为16.74μg h^(‒1)mg^(‒1)act.,其相应的法拉第效率为4.07%.具有半导体特性的SnS_(2)能够限制表面电子的可及性,进而抑制1T’-MoS_(2)的HER过程,而具有金属性的1T’-MoS_(2)可与SnS_(2)形成Mo-Sn-Sn三元催化活性位点,提高SnS2的NRR电催化活性.此外,高分辨透射电镜,X射线衍射和X射线光电子能谱结果表明,MoS_(2)-SnS_(2)/PVIPS/PPy/GO在NRR使用前后存在显著差异,这主要归因于在NRR过程中MoS_(2)-SnS2异质纳米片发生了不可逆的晶体相变.部分1T’-MoS_(2)和SnS_(2)与N_(2)发生电化学反应形成Mo‒N和Sn‒N键,不可逆地相转变为Mo_(2)N和SnxNz;部分SnS_(2)由于电化学体系中电源的还原作用而不可逆地演化为SnS.本文为优化TMDCs的制备方法及其电催化活性提供了新的设计思路.