α-MnO2 as an advanced bifunctional ORR/IOR electrocatalyst for Zn-air battery
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摘要: 析氧反应(oxygen evolution reaction, OER)和氧还原反应(oxygen reduction reaction, ORR)是可充电锌空电池(rechargeable Zn-air batteries, RZABs)重要的两个反应。其中,析氧反应具有较高的热力学平衡电位和复杂的反应路径,实际应用中需要高的充电电压驱动其发生,这将带来一系列问题并且限制了RZABs的商业化应用。基于此,本研究成功构造α-MnO2并作为ORR/IOR双功能催化剂。在碱性体系中引入反应改性剂KI,α-MnO2对碘离子氧化反应(iodide oxidation reaction, IOR)具有更低的阳极氧化电位和更快的催化动力学。当1.0 mol/L KOH电解液中添加0.5 mol/L KI时,相比于OER(1.709 V @10 mA/cm2),α-MnO2在IOR过程中电流密度达到10 mA/cm2时阳极电位减小了398 mV(1.311 V vs. RHE),且表现出低至57.5 mV/dec塔菲尔斜率。相对于与Pt/C,在含有KI的KOH电解液中,α-MnO2表现出与Pt/C相媲美的ORR活性。此外,以α-MnO2为空气电极组装成RZAB后,该电池也表现出了优异的充电活性和良好的循环寿命,在5 mA/cm2电流密度下,充放电电压间隙由0.97 V缩减为0.61 V,能量转换效率由54.9%提升至66.2%。Abstract: Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are important reactions for rechargeable Zinc-air batteries (RZABs). Unfortunatly, OER holds a high thermodynamic equilibrium potential and complex reaction path, which require an large votage to derive this reaction and greatly hinder its commercial application. Herein, α-MnO2 was successfully achieved and as the bifunctional ORR/iodide oxidation reaction (IOR) electrocatalyst. In alkline media, α-MnO2 exhibits fast kinetics and low oxidation potential for IOR. Expectedly, α-MnO2 exhibits remarkable IOR activity in 1.0 mol/L KOH with 0.5 mol/L KI. Compared with potential at 10 mA/cm2 for OER (1.709 V vs. RHE), the potential at 10 mA/cm2 reduce 398 mV (1.311 V vs. RHE) for α-MnO2 during IOR process. α-MnO2 also provides small Tafel slope of 57.5 mV/dec. Additionly, α-MnO2 represents outsanding ORR performances with respect to Pt/C. As an air electrode for RZAB, the fabricated RZAB delivers excellent performances. To be specific, at 5 mA/cm2, the voltage gap between charging and discharging reduces from 0.97 V to 0.61 V, energy efficiency increses from 54.9% to 66.2%. This work provide an unique strategy to construct bifunction ORR/IOR electrocatalysts and promote the commercialization of RZABs.
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图 3 (a)α-MnO2、RuO2和Pt/C在1.0 mol/L KOH中的OER曲线;(b)α-MnO2在不同浓度KI的电解液中的LSV曲线;(c)α-MnO2、RuO2和Pt/C在1.0 mol/L KOH + 0.5 mol/L KI中的LSV曲线和(d)相应的塔菲尔斜率
Figure 3 (a) The LSV curves of α-MnO2, RuO2 and Pt/C in 1.0 mol/L KOH; (b) the LSV curves of α-MnO2 in KOH containing different concentration of KI; (c) the LSV curves of α-MnO2, RuO2 and Pt/C in 1.0 mol/L KOH containing 0.5 mol/L KI and (d) corresponding Tafel slope
图 4 (a)Pt/C在含有不同浓度的KI的1.0 mol/L KOH电解液中的LSV曲线;(b)α-MnO2和Pt/C在含有不同浓度的KI的1.0 mol/L KOH电解液中达到10 mA/cm2电流密度时的电位柱状图和(c)α-MnO2的V-t曲线
Figure 4 (a)The LSV curves of Pt/C in KOH with different concentration of KI; (b) The potential of α-MnO2 and Pt/C at 10 mA/cm2 in KOH with different concentration of KI and (c)V-t curves of α-MnO2
图 5 α-MnO2在(a)不同含量KI的0.1 mol/L KOH中CV曲线(实线为O2饱和溶液,虚线为N2饱和溶液)和(b)LSV曲线(1600 r/min),Pt/C催化剂在(c)不同含量KI的0.1 mol/L KOH中CV曲线(实线为O2饱和溶液,虚线为N2饱和溶液)和(d)LSV曲线(1600 r/min)
Figure 5 (a) CV curves (solid line is O2 saturated solution, dotted line is N2 saturated solution) and (b) LSV curves of α-MnO2 (1600 r/min) in 0.1 mol/L KOH solution containing different concentration of KI; (a) CV curves (solid line is O2 saturated solution, dotted line is N2 saturated solution) and (d) LSV curves of Pt/C (1600 r/min) in 0.1 mol/L KOH solution containing different concentration of KI
图 6 α-MnO2在0.1 mol/L KOH + 0.05 mol/L KI中(a)不同扫速下的LSV曲线和(b)相应的K-L图;α-MnO2与商业Pt/C在不同电解液中(c)α-MnO2和Pt/C的LSV曲线(实线为KOH + 1/2 KI,虚线为纯KOH)和(d)相应的ΔE(ΔE = Ej=10 – E1/2)对比
Figure 6 (a) LSV curves of α-MnO2 in 0.1 mol/L KOH with 0.05 mol/L KI under different scan rate and (b) corresponding K-L plots; (c) LSV curves of α-MnO2 and Pt/C (the solid line is KOH + 1/2 KI, dasded line is KOH); (d) the ΔE (ΔE = Ej=10 – E1/2) value of α-MnO2 and Pt/C
图 7 α-MnO2在1.0 mol/L KOH + 0.5 mol/L KI溶液中IOR测试后的(a)XRD谱图;(b)TEM;(c)高分辨TEM图片和(d)Mn 2p的高分辨XPS光谱谱图;α-MnO2在0.1 mol/L KOH + 0.05 mol/L KI溶液中ORR测试后的(e)XRD谱图;(f)TEM;(g)高分辨TEM图片和(h)Mn 2p的高分辨XPS光谱谱图
Figure 7 (a) XRD pattern; (b) TEM; (c) high resolution TEM image and (d) high-resolution XPS spectrum of Mn 2p of α-MnO2 after IOR testing in 1.0 mol/L KOH + 0.5 mol/L KI solution; (e) XRD pattern; (f) TEM; (g) high resolution TEM image and (h) high-resolution XPS spectrum of Mn 2p of α-MnO2 after ORR testing in 0.1 mol/L KOH + 0.05 mol/L KI solution
表 1 不同催化剂的IOR比较
Table 1 Comparison of IOR of different catalysts
Catalyst Electrolyte IOR potential EOER - EIOR
(@10 mA/cm2)Ref. 20% Pt/C 1.0 mol/L KOH + 0.5 mol/L KI 1.24 V @10 mA/cm2 450 mV [5] RuTiO-550 0.1 mol/L KOH + 0.1 mol/L NaI 1.29 V @10 mA/cm2 —— [30] Ni-Co(OH)2 NSAs 1.0 mol/L KOH + 0.33 mol/L KI 1.32 V @50 mA/cm2
1.33 V @100 mA/cm2320 mV [31] Pt/RuO2/CC 0.1 mol/L KOH + 0.033 mol/L KI 1.42 V @10 mA/cm2 310 mV [45] α-MnO2 1.0 mol/L KOH + 0.5 mol/L KI 1.311 V @10 mA/cm2 398 mV this work 表 2 不同催化剂的ORR和ΔE比较
Table 2 Comparison of ORR and ΔE of different catalysts
Catalyst E1/2/V Ej=10/V ΔE (Ej=10 – E1/2)/V Reference MnO2-IL0.5 0.83 1.624 0.794 [8] 24Co-MnO2 0.787 1.66 0.872 [44] MnO2/NRGO-Urea 0.80 1.69 0.89 [47] MnO2/C 0.67 1.75 1.08 [47] CoO:MnO2@C-CC 0.78 1.45 0.67 [48] MnO-FeCo 0.88 1.501 0.621 [49] α-MnO2/Co3O4 0.76 1.784 1.024 [50] MC@NC-0.3 0.82 1.59 0.77 [51] CoFe@CNT/MnO 0.85 1.423 0.573 [52] α-MnO2 0.746 1.311 V(IOR) 0.565 this work -
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