Research progress on carbon-based non-metallic nanomaterials as catalysts for the two-electron oxygen reduction for hydrogen peroxide production
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摘要: 电催化二电子氧还原反应(2e-ORR)制备过氧化氢(H2O2)凭借其高效、安全和绿色特点,逐步发展为一种可能替代工业蒽醌法的新途径。碳基纳米材料具有电子导电性高、结构稳定性好、纳米结构调控容易、成本低等优势,是一类具有良好前景的2e-ORR制备H2O2的催化剂。针对该类碳基电催化材料的发展现状及相应材料上的活性中心和反应机制进行详细论述有助于对本领域的最新进展实现全面、系统的认识。本文首先介绍了氧还原反应的四电子、二电子反应路径及相关机制;其次,综述了提高碳基纳米材料二电子氧还原活性和H2O2生成选择性的结构优化策略及其活性中心的设计思路,包括非金属单原子掺杂、双原子掺杂、结构缺陷和表面修饰等。最后,展望了电催化制备H2O2及相关催化材料的发展前景和面临的挑战。Abstract: The electrocatalytic two-electron oxygen reduction reaction (2e-ORR) is an effective, safe and green method to produce hydrogen peroxide (H2O2) as an alternative to the industrial anthraquinone process. Carbon-based nanomaterials with the advantages of high electrical conductivity, good structural stability, easy control of the nanostructure and low cost, are recognized as promising catalysts for H2O2 production by 2e-ORR. A detailed overview of the research progress on these carbon-based electrocatalysts, their intrinsic active centers and reaction mechanisms is helpful to obtain a comprehensive and systematic understanding of the latest progress in this field. Fundamental aspects and mechanisms of the two-electron and four-electron pathways for the ORR are introduced, followed by a comprehensive review of strategies to modify carbon-based nanomaterials such as single, dual or multiple heteroatom doping, defect design and surface modification, in order to obtain high activity and selectivity for H2O2 synthesis. Finally, the prospects and challenges in obtaining catalysts with high rate and yield are presented, which should shed light on future scientific research and their use for H2O2 synthesis.
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1. 2e− and 4e− pathways in electrocatalytic ORR. 2e-ORR: orange arrow; 4e-ORR: green arrow[19]. Reprinted with permission.
图 1 非金属掺杂碳催化剂用于二电子氧还原制备H2O2的常见策略:O-掺杂碳[31],B-掺杂碳[32],N-掺杂碳[33],F/N-共掺杂碳[34],O/N-共掺杂碳[35],B/N-共掺杂碳[36],碳骨架边缘缺陷设计[37],表面活性剂改性(OCB-PAA)[38]和多孔结构设计[39]
Figure 1. Design strategies of non-metal-doped carbon electrocatalysts for two-electron oxygen reduction to H2O2, including O-doped carbon[31], B-doped carbon [32], N-doped carbon [33], F/N co-doped carbon [34], O/N co-doped carbon [35], B/N co-doped carbon [36], edge site-rich carbon [37], OCB-PAA [38] and porous carbon[39]. Reprinted with permission.
图 2 (a)CNTs和(b)O-CNTs的TEM照片.(c)CNTs和O-CNTs催化剂在0.1 mol L−1 KOH中的2e-ORR性能(LSV曲线)和(d)在相应电位下的H2O2选择性曲线.(e-f)不同氧官能团下ORR活性位点结构模型,以及计算出的二电子(实心黑色)ORR火山图[46].(g)F-mrGO和F-mrGO(600)的活性位点的结构示意图[31]
Figure 2. TEM images of (a) CNTs and (b) O-CNTs. (c) The 2e-ORR performance (LSV curves) of CNTs and O-CNTs catalysts in 0.1 mol L−1 KOH and (d) the calculated H2O2 selectivity at corresponding potentials. (e-f) DFT results of the ORR active sites under different oxygen functional groups, and the calculated two-electron (solid black) ORR-related volcano plot for the electro-reduction of oxygen to H2O2 displayed with the limiting potential plotted as a function of ∆GOOH* [46]. (g) Idealized schemes of proposed low-overpotential active sites on F-mrGO and the F-mrGO (600) [31]. Reprinted with permission.
图 3 不同氧化炭材料的X射线吸收近边结构(XANES):(a)C K-edge和(b)O K-edge.(c)0.1 mol L−1 KOH 溶液中的2e-ORR性能,以及(d)相应的H2O2产率.(e)H2O2 (JK, H2O2) 电流与材料中羰基含量的关系.(f)含有羰基、羧基或醚基的不同有机分子的2e-ORR性能.(g-h)碳骨架中含氧基团的结构示意图及其对*OOH中间体的吸附能力计算结果,其中碳:灰色;氧,红色;氢:白色[6]
Figure 3. The soft X-ray absorption near-edge structure (XANES) of different oxidated carbon materials: (a) C K-edge and (b) O K-edge. (c) Their 2e-ORR performance in 0.1 mol L−1 KOH solution, and (d) the corresponding H2O2 yield ratio. (e) The relationship of the current of H2O2 (
$J_{{\rm{K}},{{\rm{H}}_2}{{\rm{O}}_2}} $ ) and the quinone content in the materials. (f) The polarization curves of different standalone molecules with quinone, carboxylic acid, and etheric ring groups. (g-h) Theoretical analysis of different oxygenated groups, the atomic structures of the examined oxygen functional groups. Color code: carbon, gray; oxygen, red; hydrogen, white [6]. Reprinted with permission.图 4 (a)0.1 V vs. RHE下,不同N-掺杂炭材料内N含量与H2O2选择性之间的关系[54],(b)基本氮缺陷类型(吡啶-N或石墨-N)和不同吡啶-N构型(SV+1N、SV+2N和SV+3N)的示意图,及(c,d)具有不同氮缺陷结构和吡啶-N构型的多种N-掺杂CNTs材料的2e-ORR性能[55].(e-f)不同热解温度得到的三种(N-FLG-8、N-FLG-12和N-FLG-16)碳纳米片的XANES光谱,及其在0.10 mol L−1 KOH条件下H2O2选择性,(g)该材料的氧还原位点揭示[33]
Figure 4. (a) The relationship between the total content of doped N and the H2O2 selectivity at 0.1 V for different N-doped carbons[54], (b) the basic nitrogen defects (pyridinic-N or graphitic-N) and different pyridinic N configurations (SV + 1N, SV + 2N, and SV + 3N), (c, d) different N-doped CNT consists of tunable basic nitrogen defects and pyridinic N configurations and their 2e-ORR performance [55]. (e-f) XANES spectra of N-FLG-8, N-FLG-12 and N-FLG-16 and the 2e-ORR performance of N-FLG in 0.10 mol L−1 KOH and (g) the proposed two-electron and four-electron ORR pathways on N-FLG with different nitrogen configurations [33]. Reprinted with permission.
图 5 (a)F-掺杂多孔炭催化剂的2e-ORR性能曲线[57],(b)S-掺杂空心炭球H2O2合成选择性 [58].(c)B-掺杂炭材料(B-C)的背散射电子(BSE)图像及其相应的(d)碳和(e)硼元素的波长色散光谱(WDS)映射.(f)B-、P-、N-和S-掺杂的炭材料内最优的*OOH吸附构型及其(g)氧还原路径的能量变化图。绿色、橙色、蓝色、黄色、灰色、红色和白色球体分别代表B、P、N、S、C、O和H.(h-i)B-C材料在碱性条件下的2e-ORR性能图[32]
Figure 5. (a) The corresponding H2O2 selectivity of F-doped porous carbon catalysts [57] and (b) S-doped hollow carbon spheres [58]. (c) Back-scattered electron (BSE) image of B-C sample and corresponding wavelength-dispersive spectroscopy (WDS) elemental mappings for (d) carbon and (e) boron. (f) Preferred *OOH adsorption configurations on B-, P-, N-, and S- doped graphene, respectively. Green, orange, blue, yellow, gray, red, and white spheres represent B, P, N, S, C, O and H, respectively. (g) Free-energy profile of O2 reduction paths. (h-i) 2e-ORR performance of B-C in 0.1 mol L−1 KOH[32]. Reprinted with permission.
图 6 (a)具有不同氧化基团的N-掺杂炭材料的理论分析[35],(b)N/O-共掺杂多孔炭和(c-d)在0.10 mol L−1 KOH中的2e-ORR性能[62]
Figure 6. (a) Theoretical analysis of N-doped carbon materials with different oxygenated groups[35], (b) N/O co-doped porous carbon and the (c-d) 2e-ORR performance in 0.10 mol L−1 KOH[62]. Reprinted with permission.
图 7 (a)BN-C1样品的SEM和(b)不同B-C样品的元素组成,(c)B/N共掺炭材料中可能的B/N位点结构及其对OH*的结合能,(d-e)不同B/N共掺炭材料在0.1 mol L−1 KOH溶液中的2e-ORR性能[36].(f)N/P共掺炭材料的H2O2选择性[63].(g-i)N/F-共掺杂碳原子的TEM和元素分布及其 2e-ORR性能[34]
Figure 7. (a) The SEM of BN-C1 sample and (b) the composition of different B-C samples. (c) The theoretical analysis about H2O2 synthesis of B/N co-doped carbon materials with different B/N sites. (d) The 2e-ORR performance (LSV curves) of different B/N co-doped carbon materials in 0.1 mol L−1 KOH and (e) the calculated H2O2 selectivity at corresponding potentials[36], (f) the H2O2 selectivity of N/P co-doped carbons [63], and (g-i) the TEM and corresponding elements mappings of N/F co-doped carbons, and their 2e-ORR performance[34]. Reprinted with permission.
图 8 碳基材料的二电子氧还原为H2O2的其它策略:(a-b)具有蜂窝状多孔炭纤维材料及其2e-ORR性能[39];(c-e)具有优良O2扩散能力的介孔炭及其2e-ORR性能[30];(f-g)富含边缘缺陷结构的氧掺杂碳纳米片材料及其2e-ORR性能[37]
Figure 8. Other strategies to two-electron oxygen reduction to H2O2 for carbon-based materials: (a-b) Honeycomb carbon nanofibers with superhydrophilic O2-Entrapping features and the 2e-ORR performance[39]. (c-e) The mesoporous carbon spheres with effcient oxygen diffusion and their 2e-ORR performance[30]. (f-g) The active edge site-rich nanocarbon catalyst and the 2e-ORR performance[37]. Reprinted with permission.
图 9 碳基材料的二电子氧还原为H2O2的其它策略:(a-c)表面活性剂的原位界面工程,用于无金属碳和2e-ORR性能[38]. (d-f)具有超疏水空气扩散层的碳纤维基电极材料及2e-ORR性能[64]
Figure 9. Other strategies to two-electron oxygen reduction to H2O2 for carbon-based materials: (a-c) In situ interface engineering with surfactants for metal-free carbon and the 2e-ORR performance[38]. (d-f) The carbon cloth based electrode with a superhydrophobic three-phase interface by natural air diffusion and its 2e-ORR performance[64]. Reprinted with permission.
表 1 最近文献报道的碳基催化剂的2e-ORR性能
Table 1. Performances of recently reported catalysts for ORR to afford H2O2.
Electrocatalysts Electrolyte Selectivity (H2O2%) Onset potential
(vs. RHE)Ref./Year O-CNTs 0.1 mol L−1 KOH 90 % ~0.75 V 2018[46] 0.1 mol L−1 PBS ~85 % ~0.50 V Few-layer rGO 0.1 mol L−1 KOH ~100 % 0.78 V 2018[31] GNPC=O 0.1 mol L−1 KOH >90 % ~0.82 V 2020[6] OCNS 0.1 mol L−1 KOH >90 % ~0.82 V 2021[47] O-GOMC 0.1 mol L−1 KOH >90 % ~0.82 V 2021[48] NCMK-3 0.1 mol L−1 KOH ~80 % ~0.75 V 2018[54] 0.1 mol L−1 K2SO4 ~75 % ~0.45 V 0.1 mol L−1 H2SO4 ~95 % ~0.35 V N-FLG 0.1 mol L−1 KOH >95 % ~0.76 V 2020[33] FPC 0.05 mol L−1 H2SO4 ~80 % ~0.30 V 2018[57] HPCS-S 0.1 mol L−1 KOH ~70 % ~0.75 V 2019[58] B-C 0.1 mol L−1 KOH ~90 % ~0.76 V 2021[32] 0.1 mol L−1 Na2SO4 ~75 % ~0.40 V N/O co-doped 0.1 mol L−1 KOH >90 % ~0.78 V 2021[62] N+COOH 0.1 mol L−1 KOH >90 % 0.80 V 2019[35] B/N co-doped 0.1 mol L−1 KOH ~80 % 0.80 V 2018[36] P/N co-doped 0.1 mol L−1 KOH ~85 % 0.70 V 2021[63] F/N co-doped 0.1 mol L−1 KOH ~80 % ~0.77 V 2020[34] 0.05 mol L−1 H2SO4 >80 % ~0.72 V CB+CTAB 0.1 mol L−1 KOH >90 % ~0.75 V 2020[38] Edge-rich Carbon 0.1 mol L−1 KOH >90% ~0.78 V 2019[37] Home-like porous carbon fiber 0.1 mol L−1 KOH >90 % ~0.85 V 2021[39] -
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