Partially surface exposed CoFe2O4 anchored on N-doped carbon endows its high performance for oxygen evolution reaction
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摘要: 开发价格低廉、储量丰富、高效的析氧反应(OER)电催化剂对于可持续能源的转换具有重要意义。目前，虽然尖晶石型二元过渡金属氧化物表现出了很有潜力的OER活性，但其固有的低电导率一定程度上降低了其电化学性能。本文提出了一种通过金属有机框架(MOF)辅助合成表面部分暴露的CoFe2O4纳米颗粒负载在氮掺杂碳基底上(CoFe2O4@NC)的方法，且CoFe2O4@NC具有优良的催化活性。在碱性介质中，CoFe2O4@NC表现出了优异的OER活性，在10 mA·cm−2电流密度的过电势仅为1.517 V，Tafel斜率为87 mV·dec−1，这是由于CoFe2O4@NC具有足够暴露的活性位点和较高的电子转移能力。此外，CoFe2O4@NC能稳定运行15 h，具有出色的稳定性。该工作将为探索经济高效的OER电催化剂开辟一条新途径，替代贵金属在可再生能源转换中应用。Abstract: The exploration of earth-abundant and high-efficiency electrocatalysts for the oxygen evolution reaction (OER) is of great significant for sustainable energy conversion applications. Although spinel-type binary transition metal oxides represent a class of promising candidates for water oxidation catalysis, their intrinsically inferior electrical conductivity could decrease their electrochemical performances to some extent. Here, we present an metal-organic frame (MOF)-assisted synthesis of partially surface exposed CoFe2O4 nanoparticles anchored on nitrogen doped carbon substrate (NC), which can act as the superior catalyst for OER. With enough exposure of active sites and high electron transfer capability and durability, CoFe2O4@NC show a low overpotential of 1.517 V at 10 mA · cm−2 with a Tafel slope of 87 mV · dec−1 in alkaline medium. Moreover, it delivers an outstanding stability with small degradation after 15 h operation. The present work would open a new avenue for the exploration of cost-effective and efficient OER electrocatalysts to substitute noble metals for various renewable energy conversion applications.
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图 1 CoFe2O4@氮掺杂碳衬底(NC)催化剂制备过程示意图
Figure 1. Schematic diagram of the preparation process of the CoFe2O4@nitrogen doped carbon substrate (NC) catalyst
图 2 CoFe2O4@NC的XRD图谱(a)和SEM图像(b)
Figure 2. XRD pattern (a) and SEM image (b) of CoFe2O4@NC
图 3 ((a)~(b)) CoFe2O4@NC的TEM图像；(c) CoFe2O4@NC中纳米颗粒的HRTEM图像；(d) CoFe2O4@NC的Raman图谱
Figure 3. ((a)-(b)) TEM images of CoFe2O4/NC; (c) HRTEM images of nanoparticles in CoFe2O4/NC; (d) Raman spectra of CoFe2O4/NC
图 5 CoFe2O4@NC结构中Co2p (a)、Fe2p (b)、O1s (c)、Cl2p (d)、C1s (e) 和N1s (f) 的高分辨率XPS光谱
Figure 5. High-resolution XPS spectra of Co2p (a), Fe2p (b), O1s (c), Cl2p (d), C1s (e) and N1s (f) of CoFe2O4@NC
图 6 (a) CoFe2O4@NC-X(X=350、450、550℃)催化剂在1 mol/L KOH中的极化曲线；(b) 根据图6(a)中的极化曲线得出的CoFe2O4@NC-X(X=350、450、550℃)的塔菲尔斜率；((c)~(e)) CoFe2O4@NC-X(X=350、450、550℃)在不同扫描速率(20~120 mV·s−1)下的CV曲线；(f) 双层电容(Cdl)和相对电化学活性表面积
Figure 6. (a) Polarization curves of CoFe2O4@NC-X (X=350, 450, 550℃) catalyst in 1 mol/L KOH; (b) Tafel slopes of CoFe2O4@NC-X (X=350, 450, 550℃) derived from Polarization curves in Fig. 6(a); ((c)-(e)) Voltammograms of the CoFe2O4@NC-X (X=350, 450, 550℃) at various scan rates (20-120 mV·s−1) ; (f) Double layer capacitance (Cdl) and relative electrochemically active surface area
RHE—Reversible hydrogen electrode; j—Electric current density; janodic—Anodic current density; jcathodic—Cathodic current density
图 7 (a) CoFe2O4@NC-X(X=350、450、550℃)的EIS图；不同摩尔比催化剂的极化曲线 (b) 和相应的塔菲尔曲线 (c)；(d) CoFe2O4@NC-450℃在1 mol/L KOH中的计时电位测试
Figure 7. (a) Nyquist plots of CoFe2O4/NC-X (X=350, 450, 550℃); Polarization curves obtained with different proportions of catalysts (b) and corresponding Tafel plots (c); (d) Chronoamperometric measurement of CoFe2O4/NC-450℃ in 1 mol/L KOH
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