Fabrication of self-supported Cu3N electrode for electrocatalytic nitrogen reduction reaction
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摘要: 利用可再生能源衍生电力电催化氮气(N2)还原制氨(NH3)为实现绿色可持续发展提供了新思路,但该过程需要高效率、高选择性和高稳定性的廉价电催化剂。过渡金属氮化物(TMNs)由于其独特的电子结构和催化机理近年来被广泛研究应用于电催化氮气还原反应(NRR),但是目前关于氮化铜材料的电催化NRR研究报道较少。本研究采用简单一步氮化法将泡沫铜(CF)高温氮化制备了三维自支撑型氮化铜电极(Cu3N/CF),通过各种表征手段对该电极进行了系统的结构分析和形貌表征,并研究了其在中性条件下的电催化NRR性能和稳定性。结果表明,在0.1 mol/L Na2SO4溶液中,Cu3N/CF电极在−0.2 V的电位下具有最佳的电催化NRR性能,其NH3速率为1.12 × 10−10 mol/(s·cm2),法拉第效率为1.5%,并且表现出优异的电催化循环稳定性和结构稳定性。Abstract: Electrocatalytic reduction of nitrogen (N2) to ammonia (NH3) by renewable energy-derived electricity provides a new route for sustainable development. But this process requires high-efficiency, high-selectivity and high-stability, inexpensive electrocatalysts. Owing to the unique electronic structure and catalytic mechanism, transition metal nitrides (TMNs) have been widely investigated as electrocatalysts for nitrogen reduction reaction (NRR) in recent years. However, to date, copper nitride-based materials are rarely reported for NRR. In this study, a three-dimensional self-supported copper nitride electrode (Cu3N/CF) was prepared by a simple one-step high-temperature nitridation of copper foam (CF). The structure and morphology of Cu3N/CF were systematically characterized and its NRR catalytic performance and stability were evaluated in neutral media. The results show that Cu3N/CF electrode achieves high ammonia generation rate (1.12 × 10−10 mol/(s·cm2) and faradaic efficiency (1.5%) at −0.2 V vs RHE in 0.1 mol/L Na2SO4. In addition, it also exhibits excellent electrocatalytic cycle stability and structural stability.
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Key words:
- N2 reduction reaction /
- transition metal nitride /
- electrocatalysis /
- copper nitride
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图 2 一系列标准质量浓度的
${\rm{NH}}_4^+ $ 溶液的(a)UV-vis谱图和(b)在655 nm处的浓度-吸光度线性拟合曲线;一系列标准质量浓度的N2H4溶液的(c)UV-vis谱图和(d)在455 nm处的浓度-吸光度线性拟合曲线Figure 2 (a) UV-vis absorption spectra and (b) the corresponding calibration curve of various
${\rm{NH}}_4^+ $ concentrations; (c) UV-vis absorption spectra and (d) the corresponding calibration curve of various N2H4 concentrations图 3 (a)Cu3N/CF电极分别在饱和Ar和N2的0.1 mol/L Na2SO4溶液中的LSV曲线;(b)Cu3N/CF电极在饱和N2电解液中开路电位下电解2 h后电解液的UV-vis光谱;不同方法检测获得的UV-vis谱图与对应产物的生成速率和FE:(c)靛酚蓝比色法;(d)Watt-Chrisp法;(e)NH3速率与FE;(f)N2H4速率
Figure 3 (a) LSV curves of Cu3N/CF in Ar- and N2-saturated 0.1 mol/L Na2SO4, (b) UV-vis absorption spectra of the electrolyte after electrolysis of Cu3N/CF at open circuit potential in N2-saturated electrolyte for 2 h, UV-vis absorption spectra of the electrolyte by different detection methods and the corresponding product formation rate and FE, (c) Indophenol blue method;,(d) Watt-Chrisp method; (e) NH3 generation rate and FE, (f) N2H4 generation rate
图 4 (a)CF与Cu3N/CF电极在−0.2 V电位下的电催化产NH3速率对比;(b)CF与(c)Cu3N/CF电极在0.1 mol/L Na2SO4溶液中不同扫描速率下的CV曲线;(d)CF与Cu3N/CF电极的电容电流-扫描速率关系曲线
Figure 4 (a) NH3 generation rates for CF and Cu3N/CF at −0.2 V vs. RHE in 0.1 mol/L Na2SO4, CV curves for (b) CF and (c) Cu3N/CF with various scan rates in 0.1 mol/L Na2SO4, (d) capacitive current as a function of scan rate for CF and Cu3N/CF
图 5 (a)Cu3N/CF电极在−0.2 V电位下的电解曲线;(b)Cu3N/CF电极在电解前后的XRD谱图;(c)Cu3N/CF电极电解后的SEM照片;(d)Cu3N/CF电极循环电解五次的产NH3速率与FE
Figure 5 (a) Long-term electrolysis curve of Cu3N/CF at −0.2 V,(b) XRD patterns of Cu3N/CF before and after electrolysis,(c) SEM image of Cu3N/CF after electrolysis,(d) recycling test of Cu3N/CF at −0.2 V
图 6 (a)Mars-van Krevelen催化机理(蓝色、绿色和黄色球分别代表H、N和Cu原子);(b)Cu3N/CF电极在Ar气氛下电解2 h电解液的UV-vis光谱;Cu3N/CF电极在Ar气氛下电解前后的(c)XRD谱图和(d)EDX谱图
Figure 6 (a) Proposed Mars-van Krevelen mechanism (blue, green, and yellow balls represent H, N, and Cu atoms, respectively), (b) UV-vis absorption spectrum of the Ar-saturated electrolyte after electrolysis of Cu3N/CF, (c) XRD patterns and (d) EDX spectra of Cu3N/CF before and after electrocatalysis of Cu3N/CF in Ar-saturated electrolyte
表 1 Cu3N/CF与其它电催化剂产NH3速率和FE的比较
Table 1 Comparison of NH3 generation rate and FE for Cu3N/CF with other reported electrocatalysts
Catalyst Electrolyte Potential/V NH3 generation rate/(mol·s–1·cm–2) FE/% Ref. Cu3N/CF 0.1 mol/L Na2SO4 −0.2 1.12 × 10−10 1.5 this work W2N3 nanosheet 0.10 mol/L KOH −0.2 3.8 × 10–11 11.67 [21] Mo2N nanorod 0.1 mol/L HCl −0.3 78.4 (μg·h−1·mgcat. −1) 4.5 [22] VN nanoparticles 1 mol/L H2SO4 −0.1 3.3 × 10–10 6 [14] Mo nanofilm 0.01 mol/L H2SO4 −0.49 3.09 × 10–11 0.72 [29] CP2TiCl 1.0 mol/L LiCl −1 9.5 × 10–10 0.23 [30] VN nanosheet 0.1 mol/L HCl −0.5 8.40 × 10–11 2.25 [31] Fe2O3/CNT KHCO3 −2 3.58 × 10−12 0.15 [32] Fe3O4/Ti 0.1 mol/L Na2SO4 −0.4 5.6 × 10−11 2.6 [33] MoS2 0.1 mol/L HCl −0.5 8.48 × 10−11 0.096 [34] Ru/C 2 mol/L KOH −1.02 3.43 × 10−12 0.28 [35] -
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