Core-shell structured CoxHyPO4/NiCo2S4 composites towards electrocatalytic oxygen evolution
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摘要: 探索具有优异活性和稳定性的非贵金属析氧反应(OER)电催化剂是电解水制氢的关键。本文采用光还原沉积方法将无定形的非晶物质磷酸氢钴(CoxHyPO4,简称Co-Pi)沉积在多孔NiCo2S4 (NCS)蛋黄-蛋壳微球表面,成功制备出具有核壳结构的Co-Pi/NCS复合材料。密度泛函理论(DFT)计算与实验研究相结合,探究Co-Pi的引入对NCS电子结构和电催化性能的影响。异质界面的形成及化学键的重构可以提升Co-Pi/NCS的电导率,调节催化剂与反应中间体之间的电荷转移,从而改变吸附强度和反应的吉布斯自由能,最终优化OER催化活性。因此,Co-Pi/NCS表现出良好的催化活性和耐久性,在10 mA·cm−2电流密度下的过电位仅为335 mV,并且在1 mol/L的KOH溶液中能保持14 h的长时稳定性。这项工作可以促进过渡金属硫化物在电化学制氧过程中的应用。Abstract: Exploring non-precious metal oxygen evolution reaction (OER) electrocatalysts with high activity and stability is pivotal for electrolytic hydrogen production. Herein, we employ a photo-reduction deposition technique to load amorphous cobalt hydrogen phosphate (CoxHyPO4, denoted as Co-Pi) onto the surface of porous NiCo2S4 (NCS) yolk-shell microspheres, successfully fabricating Co-Pi/NCS composite material. Through the integration of density functional theory (DFT) calculations with experimental investigations, the influence of Co-Pi introduction on the electronic structure and electrocatalytic performance of NCS is probed. The formation of heterogeneous interfaces and reconstruction of chemical bonds enhance the conductivity of Co-Pi/NCS, and modulate charge transfer between the catalyst and reaction intermediates, thereby altering adsorption strength and Gibbs free energy of the reaction, ultimately optimizing OER catalytic activity. Consequently, Co-Pi/NCS demonstrates commendable activity and durability, exhibiting low overpotential of 335 mV at current density of 10 mA·cm−2 and maintaining prolonged stability for 14 h in 1 mol/L KOH solution. This work holds promise for advancing the utilization of transition metal sulfides in electrochemical oxygen production processes.
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Key words:
- electrolysis /
- oxygen evolution reaction /
- sulfur compounds /
- core-shell structure /
- reaction kinetics
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图 2 NiCo-MOF (a) 和NCS (b) 的SEM图像;NCS的N2等温吸脱附曲线和孔径分布图 (c);0.7%Co-Pi/NCS (d)、1%Co-Pi/NCS (e)、2%Co-Pi/NCS (f) 的SEM图像;NCS (g) 和1%Co-Pi/NCS (h) 的TEM图像;1%Co-Pi/NCS的HRTEM图像 (i) 和EDS元素分布图(j)
Figure 2. SEM images of NiCo-MOF (a) and NCS (b); N2 isothermal adsorption curves and pore size distribution of NCS (c); SEM images of 0.7%Co-Pi/NCS (d), 1%Co-Pi/NCS (e) and 2%Co-Pi/NCS (f); TEM images of NCS (g) and 1%Co-Pi/NCS (h); HRTEM image (i) and EDS elemental mapping (j) of 1%Co-Pi/NCS
图 4 NCS和Co-Pi/NCS样品的LSV曲线(a)、Tafel斜率(b)、EIS曲线(c)和电化学双层电容 (Cdl) (d);NCS和1%Co-Pi/NCS样品在10 mA·cm−2电流密度下的计时电位曲线(e)及800 min测试前后的LSV曲线(f)
J—Current density; Z'—Real part of impedance; Z''—Imaginary part of impedance; RHE—Reversible hydrogen electrode
Figure 4. LSV curves (a), Tafel slopes (b), EIS plots (c), and electrochemical double layer capacitance (Cdl) (d) of NCS and Co-Pi/NCS samples; Chronopotential curves under current density of 10 mA·cm−2 (e) and LSV curves before and after 800 min testing (f) of NCS and 1%Co-Pi/NCS
图 5 NCS(100) (a)、CoPO4(010) (b)和CoPO4/NCS (c)的晶体结构模型;CoPO4/NCS的差分电荷密度(d);NCS (e)、CoPO4 (f)和CoPO4/NCS (g)的态密度;NCS (h)、CoPO4 (i)和CoPO4/NCS (j)表面吸附中间体的稳定结构和自由能;NCS (k)、CoPO4 (l)和CoPO4/NCS (m)表面吸附O原子的Bader电荷
Efermi—Fermi energy; TDOS—Total density of state
Figure 5. Crystal structures of NCS(100) (a), CoPO4(010) (b) and CoPO4/NCS (c); Differential charge density of CoPO4/NCS (d); Densities of state of NCS (e), CoPO4 (f) and CoPO4/NCS (g); Stable structures and adsorption free energies of intermediates on NCS (h), CoPO4 (i) and CoPO4/NCS (j); Bader charges of NCS (k), CoPO4 (l) and CoPO4/NCS (m) adsorbed O atom
表 1 CoxHyPO4复合NiCo2S4核壳结构(Co-Pi/NCS)样品制备参数
Table 1. Preparation parameter for CoxHyPO4 complex NiCo2S4 core-shell structure (Co-Pi/NCS) sample
Sample mNCS/mg VPBS/mL VCo/μL Co-Pi content/wt% 0.7%Co-Pi/NCS 10 15 26.25 0.7 1%Co-Pi/NCS 10 15 37.5 1 2%Co-Pi/NCS 10 15 75 2 Notes: mNCS—Mass of NCS; VPBS—Volume of phosphate buffer solution (0.1 mol/L); VCo—Volume of Co(NO3)2·6H2O solution (0.5 mmol/L). 表 2 CoxHyPO4/NiCo2S4 (Co-Pi/NCS)与已报道的析氧反应(OER)电催化剂在10 mA·cm−2电流密度下的过电位比较
Table 2. Comparison of the overpotentials to achieve the oxygen evolution reaction (OER) current density of 10 mA·cm−2 for CoxHyPO4/NiCo2S4 (Co-Pi/NCS) with reported electrocatalysts
Electrocatalyst Electrolyte P/mV Ref. CoxHyPO4/NiCo2S4 1 mol/L KOH 335 This work NiCo2S4@double-layered carbon nanospheres 1 mol/L KOH 344 [16] P-doped MnCo2O4 1 mol/L KOH 364 [28] CoO/CoxP 1 mol/L KOH 370 [29] In-doped CoO/CoP 1 mol/L KOH 365 [30] Co6Ni4P/nickel foam 1 mol/L KOH 373 [31] Co9S8/MnS sulfur/nitrogen nitrogen co-doped carbon nanosheets 1 mol/L KOH 360 [32] P-doped (Zn0.33Ni0.33Mn0.33)Co2O4 1 mol/L KOH 349 [33] NiO/NiCo2O4 1 mol/L KOH 350 [34] NiCo2S4/reduced graphene oxide 1 mol/L KOH 366 [35] P-doped manganese-cobalt oxide 1 mol/L KOH 520 [36] NiCo2O4/N-doped carbon nanotubes/NiCo 1 mol/L KOH 350 [37] Note: P—Overpotential at the OER current density of 10 mA·cm−2. -
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