— 图文快解 —
通常认为钙钛矿型氧化物的ORR动力学衰减，与表面Sr的富集有关。另外，也有可能与反应气体中的污染物引起的沉积有关。但是，不论是Sr的富集，还是污染物的沉积，其详细的机理都不清楚。比如，以Sr富集为例，可能形成 致密绝缘的SrO (or Sr(OH)2/SrCO3) ，也有可能堵塞ORR的活性位点。
本文的创新点：（1）通过沉积组成成分的量，可以精细调控LSC表面（2）原位阻抗谱表征沉积SrO, Co3O4and La2O3过程的变化和电化学行为。
Figure 1: Sketch of an LSCelectrode with an inhomogeneously active surface for the oxygen reductionreaction (ORR).The LSC surface is largely but notcompletely SrO-terminated10; a few highly active sites, either Co itself or inthe vicinity of Co, catalytically enhance the ORR.
Figure 2 a, Setupduring the ablation of target material with the sample positioned below thetarget and plasma plume. b,Sample with the macroscopic 5 × 5mm2 denseLSC working electrode contacted by a Pt tip from above and the porous LSCcounter electrode connected to a Pt sheet. c,Sketch of the entire setup (WE, working electrode; CE, counter electrode).
Figure 3 RepresentativeNyquist plots normalized to the surface area of the LSC working electrode ofas-prepared thin films decorated with deposits from ‘Sr’ (a) and ‘Co’ (b)target measured in situ at 450°Cand 5 × 10−1 mbar p(O2). The legends specify the total number of laser pulsesafter which the impedance spectra were recorded.
图4 用不同材料对LSC表面修饰后，Rsurf exch的变化
Figure 4 a, Dependence of the surface exchange resistance and surfaceexchange coefficient kq on the number of laser pulses used to decorate the LSC working electrodesurface of 16 samples at 450°C in 5 × 10−1 mbar p(O2). b, Surface exchange resistanceplotted versus the amounts of cations deposited on the LSC working electrodesurface (log–log plot, lines are guides to the eye); the surface exchangecoefficientkqplotted on the rightordinate is not an independent quantity but can be simply calculated from themeasuredRsurfexch bykq = RT/(4F2Rsurf exchcO) with R being the gas constant, T the absolute temperature, F Faraday’s constant, and cO the oxygen lattice site concentration in LSC. The nominal amount ofcations needed to form a (100) perovskite monolayer is indicated as well. c, Increase of the surfaceexchange resistance relative to its initial value with ongoing deposition of‘Sr’ and ‘Sr (sc)’. Effects of ‘Sr’ and ‘Sr (sc)’ decoration are the samewithin the error bars(coloured area). Error bars show the standard deviation of the mean from threesamples including two to three measurements for each sample.
Figure 5 Decrease of the surface exchange resistance ofsamples already decorated with 88 laser pulses of the ‘Sr’, ‘Sr (sc)’ and ‘La’target after applying 10, 30 and 80 laser pulses to the ‘Co’ target at 450°C in 5 × 10−1 mbarp(O2).
Figure 6 a, Sites ofas-prepared thin films with Co termination (violet) show a higher exchange ratethan regions with Sr termination (black). b,SrO causes an activity decrease (resistance increase). c, Co-oxide decoration leads toan increase of the ORR activity. d,The surface of a SrO decorated LSC electrode can be reactivated to its initialvalue by adding Co-oxides, provided the SrO layer is not too thick yet.返回搜狐，查看更多