Nature:真假石墨烯!-正极材料
氢离子互通式立体交叉膜燃料电池(PEMFC)是最具特有的或特别的的胞衣能源资源方法通道,它将氢和氧的化学能通道电化学答复转变成电能,具有无污染、高转变率等优点,符合的多种申请命运,是亲电动车辆的抱负能源资源形成。在PEMFCs中,负极的氧复原答复(ORR)是速率把持测量,必要触媒剂催促答复,眼前依赖于贵金属触媒剂Pt/C。为了降价,助长燃料电池大规模商品化,男子汉功劳多种非铂触媒剂,首要包罗非贵金属触媒剂(以Fe-N-C塞满为代表)及非金属触媒剂(以十亿分之一公尺碳塞满为代表)。非贵金属触媒剂在现实酸性PEMFC结帐中积极的较高,但其稳固性较差,功劳稳固的非铂触媒剂具有被判为永久罪的重要意义。
从前考虑显示氮掺杂碳十亿分之一公尺塞满(石墨烯、碳十亿分之一公尺管)具有优良的燃料电池稳固性,理由了男子汉对非金属触媒剂的极大关怀(N-DopedCarbon Nanomaterials Are Durable Catalysts for Oxygen Reduction Reaction inAcidic Fuel Fells,Science Advances, 2015, 1, e1400129)。而且杂原子掺杂的碳塞满,缺陷碳也可以无效催化氧复原答复,但从前表征多是在碱性电解质中停止,在更亲PEMFC酸性命运下的功能报道略微;更,碳缺陷的方法较多,习俗碳十亿分之一公尺塞满经常同时具有多种缺陷位点,这障碍了认清详细方法碳缺陷的功能表示特性的。
迩来,现时称Beijing航天大学水江澜灌输课题组和凯斯西储大学戴黎明灌输协作,报道了zigzag碳在氢离子互通式立体交叉膜燃料电池打中高效、稳固的氧复原催化功能,论文宣布于《自然的事情传达》(DOI:),该论文作为Featurearticle被《自然的事情传达》包住于新近的Editor’ Highlights的能源资源塞满相称()。JacilynnBrant编纂评论道:“本钱和稳固性障碍了氢离子互通式立体交叉膜燃料电池的大规模申请。作者分解了具有zigzag边的石墨烯十亿分之一公尺带,将其用于电催化氧复原答复,这种非金属触媒剂在燃料电池中收购了优良的比功率和稳固性。” ( “Cost and stability of catalysts hinder widespread use of protonexchange membrane fuel cells. Here the authors synthesize zigzag-edged graphenenanoribbons for electrocatalysis of oxygen reduction. Employment of such ametal-free catalyst in a fuel cell yields remarkable power density anddurability.” )
触媒剂准备工作:率先必要寻觅具有较比单一缺陷方法的碳十亿分之一公尺塞满。石墨烯十亿分之一公尺带(GNRs)具有边的缺陷占比多的表示特性的,而且可以通道更改分解方法,调控边的的缺陷方法,比如,Tour因此其他人用浓硫酸盐和紫色盐翻开多壁碳十亿分之一公尺管,可准备工作出具有单一zigzag边的缺陷的石墨烯十亿分之一公尺带(Nature 2009,458,872-876)。到这地步,石墨烯十亿分之一公尺带是一种抱负的缺陷碳选择。只因为,石墨烯十亿分之一公尺带轻易地蜂拥,实现绝大相称边的缺陷点不克不及揭露于答复物,形成十亿分之一公尺带的催化功能不克不及使充分活动。应用相称翻开方法保存一相称碳十亿分之一公尺管作为使适合,起到戗、切割GNRs的功能;同时在催化层内累积而成气黑颗粒而且疏散GNRs,扶助向上移动催化层传质生产能力。这种催化层体系结构设计可以较大平均的地戒GNR蜂拥形成的传质成绩,将zigzag碳极大值化地揭露暴露。考虑者同时准备工作了什么价钱比例样,包罗全翻开的GNR、因此通道掺氮处置的对照组战利品N-GNR@CNT和N-GNR。
Fig. 1 Schematic illustration. The synthetic route of zigzag-type graphene nanoribbons on carbon nanotubes (GNR@CNT) from a MWCNT to b partially unzipped oxidized CNT and to c GNR@CNT. d The application as oxygen reduction reaction catalyst in a proton exchange membrane fuel cell (PEMFC). Carbon black XC-72 is used as spacer to prevent the stacking of active materials
Fig. 2 Transmission electron microscopy images and schematic diagrams. a, b Partially unzipping multiwall carbon nanotube (MWCNT) to graphene nanoribbons on carbon nanotube (GNR@CNT), c, d nitrogen-doped GNR@CNT (N-GNR@CNT), e, f totally unzipped MWCNT to graphene nanoribbons (GNR), and g, h nitrogen-doped GNR (N-GNR). Scale bar: 100 nm, and 10 nm for inset micrograph in g
半电池结帐:在碱性电解质里GNR@CNT目前的行动较高积极的,但稍弱于N-GNR@CNT,可感激氮掺杂积极的位点具有高等的的碱性积极的和氨水衰败的十亿分之一公尺孔洞失效了传质阻碍。酸性下ORR结帐弄清GNR@CNT的zigzag碳积极的位点比N掺杂的碳积极的位点具有高等的的起点电位和限定电流,这是鉴于N掺杂战利品的中二氮陆圜氮在酸性电解质中轻易被氢离子化而失效积极的,弄清对立杂原子掺杂的碳触媒剂,缺陷碳积极的点对酸性电解质命运有更的柔软性。而且的用过氧化氢漂白氢氧化物试验(PRR)显示GNR@CNT上氧复原到水的转换以目前的4电子转换认为优先。还瞥见碳缺陷的积极的对体温敏感,随命运体温增加而积极的扶助向上移动。
Fig. 3 Half-cell characterization of the catalysts. Linear sweep voltammetry curves of graphene nanoribbons on carbon nanotubes (GNR@CNT), N-doped GNR@CNT (N-GNR@CNT), and N-doped graphene nanoribbons (N-GNR) for a oxygen reduction reaction (ORR) activity, b peroxide reduction reaction (PRR) activity with 1.3 or 10 mM H2O2, and c ORR activity at 5, 25, and 35 °C in 0.1 M KOH; d ORR activity, e PRR activity with 1.3 or 10 mM H2O2, and f ORR activity at 5, 25, and 35 °C in 0.5 M H2SO4. Electrolyte was O2-saturated, except for PRR experiments with Ar-saturated electrolyte. Rotating speed: 1600 rpm. Scan rate: 10 mV s-1
PEMFC全电池结帐:GNR@CNT达到最大弥撒曲比功率520W/g-,超过了将近全部的非金属触媒剂和变得越来越大非贵金属触媒剂。触媒剂的载量、催化层厚度感情催化层传质,于是明显感情电池功能,大于正常的触媒剂载量会造成塞满应用率下斜。更为重要的瞥见是GNR@CNT的zigzag碳积极的位点目前的行动相当稳固的电池功能,在恒压、80℃、饱和度湿度氢/氧PEMFC中与氮掺对照组稳固性相当,远高于Fe-N-C触媒剂。
Fig. 4 Proton exchange membrane fuel cell evaluation. Polarization and power density curves of graphene nanoribbons on carbon nanotubes (GNR@CNT), N-dope GNR@CNT (N-GNR@CNT), and N-doped graphene nanoribbons (N-GNR) as a function of the areal current density with cathode catalyst loading of a mg cm-2 and b 0.50 mg cm-2 in a proton exchange membrane fuel cell (PEMFC); c stability of the indicated catalysts in PEMFC measured at 0.5 V. The absolute current densities before durability tests (at 100%) were 136, 80 and 1216 mA cm-2 for graphene nanoribbons on carbon nanotube (GNR@CNT), nitrogen-doped catalyst (N-GNR@CNT), and reference catalyst iron-nitrogen-carbon (Fe/N/C), respectively. Weight ratio of Nafion/ catalyst/carbon black (XC-72) = 5/1/4. Cell: 80 °C; H2/O2: 80 °C, 100% relative humidity, 2 bar back pressure
催化机械作用辨析:密度泛函观点(DFT)辨析了差额缺陷碳积极的位点的ORR转换。如图5所示,通道计算GNR中能够具有积极的的五种碳原子的ORR转换,瞥见在pH=的健康状况,zigzag碳原子具有黄金时代的氧复原积极的,它的速控步为O2àOOH步,呼应的自由能改变值ΔGOOH为,跟纯石墨烯在0.1M KOH打中人值很亲。作为比例,计算获得利益或财富的GNR打中碳原子、几乎氧的碳原子,在拐角处转弯型碳原子因此孔洞缺陷边的碳原子中在O2àOOH的答复步中均具有较大的自由能改变,这些较大的自由能改变值障碍了OOH*及水的行进,例如失效了这些碳原子位点作为催化ORR首要积极的位点的能够性。
Fig. 5 Theoretical calculations. Models (top) and the corresponding free energy diagrams (bottom) for cycled carbon atoms at electrode potential UNHE = 0 and 0.745 V in 0.5 M H2SO4 (NHE normal hydrogen electrode, RHE reversible hydrogen electrode, UNHE = URHE – 0.0591 × pH, pH = ). a Carbon atom at zigzag edge, b carbon atom in basal plane, c carbon atom at O-doped zigzag edge, d carbon atom at armchair edge, and e carbon atom near a void