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9. Formation Mechanism of Mesoporous CrN. The mechanism of formation of mesoporous CrN is similar to the case of mesoporous VN. 35 Under ammonia ﬂ ow at 700 °C, the formation of KOH or KNH2 from potassium oxide is thermodynamically possible. Other compounds such as mixed hydroxides and amides or imides may also be produced during the heating and cooling processes. In any case, these byproducts are either solids or liquids at the synthesis temperature and apparently sublime slowly during the reaction or wash out using DI water after the reaction. The observed mesoporosity in CrN results from phase separation of the nitride from the other byproducts. We hypothesize that the surface energies and diffusion constants of the relevant phases allow such separation to proceed at the mesoscale. In addition, the sintering rate of the nitride is slow enough that the porosity is not eliminated during the heating period, because the diffusion rates in nitrides are so low. This mechanism is similar to that seen in the formation of porous Vycor, where spinodal decomposition of aborosilicate glass forms two phases that are separated on the nanoscale. 42 An ordered mesoporous CrN, made using a hard silica template, with comparable high surface area (78 m 2 /g) was previously reported by Shi et al. 33 In their work, a wide range of pore-size distribution was observed (from 5 to 25 nm), which is also comparable to our CrN product. However, the present method does not require the use of a template and its subsequent removal. 10. Mesoporous CrN as Catalyst Support. Pt particles are deposited on mesoporous CrN and carbon black through a polyol process. Figure 1a shows the XRD patterns of the Pt/ CrN and Pt/C electrocatalysts in addition to the XRD patterns of the mesoporous CrN that was synthesized and used as the catalyst support. All of the di ﬀ raction peaks of mesoporous CrN are also observed in the Pt/CrN catalyst. The Pt particles crystallize in the space group Fm3̅m with re ﬁ ned lattice parameter a = 3.9311(4) Å. The di ﬀ raction peaks of Pt in the Pt/C system are almost identical to those of Pt on CrN. The weak diffraction peak observed at 2Θ ≈ 24° for Pt/C is attributed to the carbon black. The size and morphology of the Pt/CrN catalyst can be observed in Figure 2c and d. The average size of the Pt particles in the Pt/CrN catalyst is 4.5 nm, and the average size of the Pt particles in the Pt/C catalyst that was used for comparison was 4.2 nm. The difference in average Pt particle size between the two catalysts was not very large, indicating that average Pt particle size was relatively unaffected by which catalyst support was used. Pt particles are uniformly dispersed on mesoporous CrN with little obvious aggregation and have a narrow size distribution. The cyclic voltammograms of the mesoporous CrN seen in Figure 4 show that no redox peaks associated with CrN are observed when cycling between −0.8 and 1.2 V (20 mV/s vs SCE) for 10 cycles, indicating that the CrN is electrochemically stable, at least on the minutes time scale.

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9。介孔氮化鉻的形成機(jī)理。介孔氮化鉻的形成機(jī)理是類似介孔氮化釩。 35 于700℃的氨流量，從氧化鉀形成KOH或KNH 2熱力學(xué)上可能的。其它化合物如混合氫氧化物、酰胺或酰亞胺也可在過程中加熱和冷卻產(chǎn)生。任何情況下副產(chǎn)品在合成溫度是固體或液體，顯然在反應(yīng)過程中慢慢生成，反應(yīng)后使用去離子水將其洗去。氮化物與其它副產(chǎn)物相分離產(chǎn)生的孔隙可在氮化鉻中觀察到。我們假設(shè)，表面能與有關(guān)相的擴(kuò)散常數(shù)允許這種分離在中尺度繼續(xù)進(jìn)行。我們著重假設(shè)，因?yàn)榈飻U(kuò)散速率太低，氮化物燒結(jié)速率慢到孔隙不能在加熱期間消除。這一機(jī)制與硼硅酸鹽玻璃的亞穩(wěn)分解在納米尺度上形成兩相分離形成多孔質(zhì)玻璃類似。42先前施（Shi ）等人報(bào)道了使用硬硅膠模板產(chǎn)出的同比更高表面積（78米2 /克）的有序介孔氮化鉻。 33他們的工作中可見到寬范圍的孔隙尺寸分布（從5到25納米），相當(dāng)于我們的CrN產(chǎn)品。然而，現(xiàn)在的方法不需要使用模板，而后去除。 10。介孔氮化鉻作為催化劑載體。鉑顆粒和炭黑通過多元過程沉積在CrN的介孔。圖1a示出了合成并用作催化劑載體的介孔CrN的X射線衍射圖譜和Pt/氮化鉻和Pt/ C電催化劑的X射線衍射圖譜。所有的介孔CrN的衍射峰在Pt/氮化鉻催化劑也觀察到。Pt粒子結(jié)晶空間群Fm3m精確晶格參數(shù)為a =3.9311（4）唉。Pt在Pt/ C系統(tǒng)中的衍射峰幾乎與Pt在CrN上相同。因?yàn)樘亢�，�?duì)Pt / C在2Θ≈24°觀察到的衍射峰弱。Pt/氮化鉻催化劑的大小和形態(tài)如圖2c和d。Pt粒子在Pt/氮化鉻催化劑的平均大小為4.5 nm，相比較而言，Pt粒子在Pt / C催化劑平均大小為4.2nm。兩種催化劑之間平均Pt粒子大小差異不大，表明平均Pt粒大小受催化劑載體使用影響較小。Pt粒子均勻分布于介孔CrN，無明顯聚集，并具有較窄的粒徑分布。圖4的介孔CrN的循環(huán)伏安曲線，-0.8和1.2伏特（20毫伏/秒相對(duì)于SCE）進(jìn)行10周期循環(huán)觀察時(shí)，氮化鉻沒有相關(guān)的氧化還原峰出現(xiàn)。表明CrN，至少在幾分鐘的時(shí)間尺度，是電化學(xué)穩(wěn)定的。

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