【摘要】：氫能是一種清潔的無碳能源,具有儲量廣、熱值高和綠色環(huán)保等優(yōu)點,是一種理想的可再生非化石能源,然而目前氫能大規(guī)模應(yīng)用面臨廉價制氫、安全儲氫和高效用氫三個問題。在制氫方面,電解水制氫因氫氣純度高、綠色環(huán)保和工藝簡單等優(yōu)點而倍受關(guān)注,但是其能耗過大嚴重制約著其規(guī)模化應(yīng)用。能耗高的主要原因是電解池陽極催化劑的析氧超電勢過高。雖然Ru和Ir基貴金屬催化劑能有效降低超電勢,但其探明儲量少且價格高昂,難以實現(xiàn)大規(guī)模應(yīng)用,因此,開發(fā)一類活性高且穩(wěn)定性好的廉價非貴金屬析氧電催化劑具有重要的科學(xué)意義和實際應(yīng)用價值。層狀復(fù)合金屬氫氧化物(LDHs)是一種層板組成可調(diào)變、層間客體可交換的二維層狀結(jié)構(gòu)材料,而且已有文獻報道含Co、Ni、Fe或Mn等過渡金屬元素的LDHs材料或其焙燒產(chǎn)物MMO具有突出的析氧電催化性能(活性和穩(wěn)定性)。但是,LDHs類材料容易發(fā)生團聚,導(dǎo)致有效比表面減小和穩(wěn)定性下降,不利于其活性組分析氧性能的充分發(fā)揮,因此,如何可控制備不易團聚的中空微球多級結(jié)構(gòu)的高析氧性能的LDHs材料或其焙燒產(chǎn)物是件亟待解決的關(guān)鍵問題。本文基于無模板法一步水熱合成了Ni2Fe-LDH與CoxNi2-xFe-LDH中空微球材料,并對LDHs前驅(qū)體進行熱處理得到混合金屬氧化物中空微球,通過ICP-AES、XRD、SEM以及TEM等手段對樣品組成、結(jié)構(gòu)、形貌等進行詳細表征與分析,采用旋轉(zhuǎn)盤電極、循環(huán)伏安和線性掃描等電化學(xué)技術(shù)對樣品在堿性電解質(zhì)電催化性能進行表征與分析。本文的主要研究結(jié)果如下:(1)以 Ni(N03)2·6H20、Fe(N03)3·9H20 為原料,NH4F 為形貌調(diào)控劑,CO(NH2)2為沉淀劑,通過一步水熱合成法可控制得了 Ni2Fe-LDH中空微球。所制得的微球直徑尺寸在7～9 μm范圍內(nèi),組成微球的LDH片的大小約為1 μm。研究結(jié)果表明,NH4F在微球形成的過程中同時起到形貌調(diào)控與化學(xué)誘導(dǎo)自轉(zhuǎn)變作用,基于反應(yīng)時間的實驗證實微球的形成原理是Ostwald熟化。盡管在形成中空微球的過程中比表面是減少的,但是獨特的多級結(jié)構(gòu)導(dǎo)致電化學(xué)活性面積增大,當(dāng)NH4F濃度為0.4 M時,Ni2Fe-LDH中空微球的OER活性最佳,其在1 mol.L-1的KOH溶液中的η10超電勢僅為290 mV, Tafel斜率為51 mV·dec-1,優(yōu)于貴金屬Ru02的性能。此外,經(jīng)過2000次CV循環(huán)后其η10超電勢僅增加12.9%,表現(xiàn)出了優(yōu)異的電催化穩(wěn)定性。(2)以 Co(N03)2·6H2O、Ni(N03)2.6H2O、Fe(N03)3·9H20 為原料,NH4F為形貌調(diào)控劑,CO(NH2)2為沉淀劑,通過一步水熱合成法制得不同Co、Ni比例的CoxNi2-xFe-LDH中空微球材料。研究結(jié)果表明,引入的Co2+導(dǎo)致高導(dǎo)電性的NiⅢOOH在低電位更容易生成,其中Co1Ni1Fe-LDH中空微球樣品的OER活性達到最高,η10超電勢為290 mV。以CoxNi2-xFe-LDH為前驅(qū)體,通過不同溫度焙燒得到系列不同組成的ComNi2-mFeOx-MMO中空微球材料,前驅(qū)體的形貌得到完全保留。當(dāng)焙燒溫度的升高至700℃時開始逐漸出現(xiàn)燒結(jié)現(xiàn)象,在一定程度上降低樣品的電化學(xué)活性面積從而使OER與ORR活性下降。經(jīng)600℃焙燒得到的Co0.75Ni1.25FeOx-MMO材料具備最低的ΔE(EOER-EoRR)為0.95 V,優(yōu)于貴金屬氧化物IrO2材料(1.32 V),非常接近商業(yè)Pt/C (0.94V)的ΔE值。
[Abstract]:Hydrogen energy is a kind of clean carbon-free energy, has the advantages of wide storage, high heat value and green and environmental protection, is an ideal renewable non-fossil energy source, but at present, the hydrogen energy large-scale application is faced with the three problems of cheap hydrogen production, safe hydrogen storage and high-efficiency hydrogen production. In the aspect of hydrogen production, the hydrogen production of the electrolyzed water is of great concern due to the high purity of the hydrogen, the green environment protection and the simple process, but the energy consumption of the water is too large to restrict the large-scale application. The main reason for high energy consumption is that the oxygen evolution of the anode catalyst of the electrolytic cell is too high. Although the Ru and Ir-based noble metal catalysts can effectively reduce the overpotential, it is difficult to realize large-scale application, and therefore, it is of great scientific significance and practical application value to develop a kind of cheap non-noble metal oxygen-removing electrocatalyst with high activity and good stability. the layered composite metal hydroxide (LDHs) is a two-dimensional layered structure material which is composed of a laminate, an adjustable variable layer and a layer-to-layer object, and has been reported to contain Co, Ni, The LDHs material of a transition metal element such as Fe or Mn or the roasting product MMO thereof has a prominent oxygen evolution electrocatalytic performance (activity and stability). however, that LDHs material is easily agglomerated, resulting in a decrease in the effective specific surface and a decrease in stability, which is not conducive to the full play of the activity group in the analysis of the oxygen performance, and therefore, How to control the high-oxygen-performance LDHs material of a hollow micro-sphere multi-stage structure which is not easy to be agglomerated or the roasting product of the LDHs material is a key problem to be solved urgently. The hollow micro-spheres of Ni2Fe-LDH and CoxNi2-xFe-LDH were synthesized by heat treatment of LDHs precursor, and the composition, structure and morphology of the samples were characterized and analyzed by ICP-AES, XRD, SEM and TEM. The electrocatalytic properties of the samples were characterized and analyzed by electrochemical techniques such as rotating disk electrode, cyclic voltammetry and linear scanning. The main results of this paper are as follows: (1) Ni (N03) 2 路 6H20, Fe (N03) 3 路 9H20 as raw material, NH4F as the profile control agent and CO (NH2) 2 as precipitant, Ni2Fe-LDH hollow microspheres can be controlled by one-step hydrothermal synthesis. The size of the prepared micro-ball is in the range of 7-9. m u.m, and the size of the LDH sheet making up the micro-ball is about 1. m Based on the reaction time, the formation principle of microball is confirmed by Ostwald ripening. Although the specific surface is reduced during the formation of the hollow microspheres, the unique multi-stage structure results in an increase in the area of the electrochemically active area, and when the concentration of the NH4F is 0.4 M, the OER activity of the Ni2Fe-LDH hollow microspheres is best, and the OER potential in the KOH solution of 1 mol. L-1 is only 290 mV, The Tafel slope is 51 mV. dec-1, which is superior to the properties of the noble metal Ru02. In addition, after the 2000 CV cycle, the over-potential of the capacitor 10 increased by only 12. 9%, showing excellent electrocatalytic stability. (2) Co (N03) 2.6H2O, Ni (N03) 2.6H2O, Fe (N03) 3.9H20 as the raw material, the NH4F as the profile control agent, CO (NH2) 2 as a precipitating agent, and the CoxNi2-xFe-LDH hollow microsphere material with different Co and Ni ratio is prepared by one-step hydrothermal synthesis method. The results show that the introduced Co2 + results in the high conductivity of Ni-鈪，

本文編號：2430884