Preparation of high-efficiency iron-cobalt bimetallic site oxygen reduction electrocatalysts by step-by-step metal loading method

doi:10.11949/0438-1157.20240073

Abstract

Abstract:

Transition metals and nitrogen-doped carbon (M-N-C) have risen to prominence as alternatives to platinum-based catalysts, acclaimed for their superior electrocatalytic activity and comparatively lower production costs. However, current M-N-C catalysts usually involve a combination of metal salts, nitrogen-containing substances and carbon supports. The resulting catalysts after heat treatment and acid washing processes lack sufficient performance in terms of active site density and mass transfer capacity. In this paper, Fe, Co bimetallic doped M-N-C catalysts were prepared by step-by-step metal loading method. Taking advantage of the competitive effect of Zn²⁺ and Co²⁺, a small-sized and uniform Zn-Co-ZIFs bimetallic zeolite imidazole framework was successfully synthesized. Subsequently, the maximum number of Fe atoms is embedded into the C-Zn-Co-ZIFs-H⁺ precursor structure without forming metal clusters, so that it can generate a large number of FeCo—N _x active sites after pyrolysis. This refinement engenders a substantial augmentation in the Fe active site content of the FeCo-N-C-2 catalyst (1.9%, mass fraction), and a profound optimization of its microporous and mesoporous architecture (860 m²·g^-1), culminating in enhanced electrochemical activity and stability. The catalyst exhibited half-wave potentials (E_1/2) for oxygen reduction reaction (ORR) of 0.806 V in 0.1 mol·L^-1 HClO₄ and 0.921 V in 0.1 mol·L^-1 KOH, maintaining 91.21% and 95.32% of its activity respectively after 50000, 45000 s of a constant voltage test. Moreover, this catalyst has achieved peak power densities of 746 mW·cm^-2 in proton exchange membrane fuel cells (PEMFCs) and 164 mW·cm^-2 in alkaline zinc-air flow batteries (ZAFBs), demonstrating its superior performance.

Key words: catalyst, step-by-step metal loading method, iron and cobalt-based dual-metalsite, electrochemistry, oxygen reduction reaction, fuel cells, zinc-air flow batteries

摘要：

过渡金属和氮掺杂的碳（M-N-C）由于优异的电催化活性以及较低的生产成本，成为铂基催化剂的替代。然而，目前的M-N-C催化剂通常涉及金属盐、含氮物质和碳载体的结合，在经过热处理和酸洗过程后得到的催化剂在活性位点密度和传质能力上性能不足。采用分步负载金属法制备了Fe、Co双金属掺杂的M-N-C催化剂。利用Zn²⁺和Co²⁺的竞争效应，成功合成了小尺寸且均匀的Zn-Co-ZIFs双金属沸石咪唑骨架。随后，在不形成金属团簇的前提下将最大量的Fe原子嵌入C-Zn-Co-ZIFs-H⁺前体结构中，使其在热解后能产生大量的FeCo—N _x 活性位点。这种改进显著增加了FeCo-N-C-2催化剂中Fe活性位点的含量（1.9%，质量分数），并深度优化了其微孔和介孔结构（860 m²·g^-1）。该催化剂在0.1 mol·L^-1 HClO₄和0.1 mol·L^-1 KOH溶液中，氧还原反应（ORR）活性展现出了0.806 V和0.921 V的半波电位，并分别在50000、45000 s恒定电位测试后保持了91.21%和95.32%的活性。将其组装于质子交换膜燃料电池（PEMFCs）和碱性锌-空气液流电池（ZAFBs）中，峰值功率密度分别达到了746、164 mW·cm^-2，显示出优越的性能。

关键词: 催化剂, 分步负载金属法, 铁钴双金属位点, 电化学, 氧还原反应, 燃料电池, 锌-空气液流电池

CLC Number:

TQ 152

Xudong JIA, Bolong YANG, Qian CHENG, Xueli LI, Zhonghua XIANG. Preparation of high-efficiency iron-cobalt bimetallic site oxygen reduction electrocatalysts by step-by-step metal loading method[J]. CIESC Journal, 2024, 75(4): 1578-1593.

贾旭东, 杨博龙, 程前, 李雪丽, 向中华. 分步负载金属法制备铁钴双金属位点高效氧还原电催化剂[J]. 化工学报, 2024, 75(4): 1578-1593.

Figures/Tables 16

Fig.1 Synthesis and morphological characterisation of FeCo-N-C-2 catalyst

Fig.2 Structural characterisation of catalysts

Fig.3 ORR electrocatalytic activity of catalysts in acidic environment

Fig.4 ORR, OER electrocatalytic activity of catalysts in alkaline environment

Fig.5 Device performance of catalysts

Fig.A6 K-L equation curve corresponding to acidic LSV curve of FeCo-N-C-2 catalyst

Fig.A7 Acid CV curve of Fe-N-C (a), Co-N-C (b), FeCo-N-C-1 (c), FeCo-N-C-2 (d) and 20% Pt/C (e) catalysts at 1.103—1.203 V, and acid Cdl curve (f)

Fig.A8 Alkaline CV curve of FeCo-N-C-2 (a), 20% Pt/C (b) catalysts at 1.111—1.211 V; alkaline Cdl curve (c); ECSA (d)

Table A2 Alkaline ORR properties of FeCo-N-C-2 catalyst compared with other catalysts

催化剂	E_1/2/V	文献
FeCo-N-C-2	0.921	本文
f-FeCoNC900	0.890	[43]
FeCo₂-NPC-900	0.870	[44]
Fe-Zn-SA/NC	0.850	[46]
FeCo-ISAs/CN	0.920	[47]

Table A3 Alkaline OER properties of FeCo-N-C-2 catalyst compared with other catalysts

催化剂	过电位/V	Tafel斜率/（mV·dec^-1）	文献
FeCo-N-C-2	0.339	65.59	本文
Co-Fe-N-C	0.309	37.00	[48]
Fe₂/Co₁-GNCL	0.350	70.00	[49]
CoDNi-N/C	0.360	72.00	[50]
Fe-NiNC-50	0.340	54.00	[51]

Fig.A1 Preparation of Fe-N-C (a), Co-N-C (b) and FeCo-N-C-1 (c) catalysts

Fig.A2 TEM image of ZIF-8 precursor

Fig.A3 XRD pattern of Zn-Co-ZIFs precursor

Fig.A4 TEM images of Fe-N-C (a), Co-N-C (b) and FeCo-N-C-1 (c) catalysts

Fig.A5 Parameters optimization of reactant concentration (a), reactant ratio (b), reaction temperature (c) and reaction time (d)

Table A1 Acid ORR properties of FeCo-N-C-2 catalyst compared with other catalysts

催化剂	E_onset/ V	E_1/2/V	文献
FeCo-N-C-2	0.999	0.806	本文
f-FeCoNC900	0.870	0.810	[43]
FeCo₂-NPC-900	0.850	0.740	[44]
FeNi-N₆	0.900	0.790	[45]
Fe-Zn-SA/NC	0.870	0.780	[46]

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