Organic xerogels combined with iron and nitrogen as PGM-free catalysts for the oxygen reduction reaction

Álvarez-Manuel, Laura; Alegre, Cinthia; Sebastián, David; Lázaro, M.J.

doi:10.1016/j.ijhydene.2023.06.184

Cited by 4 publications

(12 citation statements)

References 70 publications

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“…While macro- and mesoporosity are modified in the polymerization step by varying the synthesis pH, microporosity can be tuned in the pyrolysis step [ 82 , 83 ]. In the single-stage process following the procedure outlined in our previous work [ 44 ], OXG undergoes carbonization simultaneously with Fe and N doping. This results in a fast carbonization, with a short time to form micropores, also entailing the collapse of the structure because of the fast evaporation of volatile species.…”

Section: Resultsmentioning

confidence: 99%

“…In a previous work [ 44 ], we synthesized Fe-N-C catalysts through a one-step template-free approach using CXG as a matrix, proving the feasibility of this carbonaceous structure as a matrix for iron- and nitrogen-based catalysts. To achieve this, iron and nitrogen precursors were mixed with an organic xerogel (prior to carbonization) and treated at 1050 °C for 1 h, leading to N and Fe doping and formation of a porous structure simultaneously.…”

Section: Introductionmentioning

confidence: 86%

“…In the second, the previously prepared CXG- n (2 g) was dispersed via sonication in 30 mL of deionized water. The solution containing the urea and FeAc and the carbon-containing solution were then mixed and magnetically stirred for 1 h. The powder was ground in a planetary ball mill for three hours, following the procedure described in previous works [ 44 , 50 ]. The ball to powder ratio was 40:1 [ 51 , 52 ].…”

Section: Methodsmentioning

confidence: 99%

“…To determine the quantity of electrons transferred, the polarization curves were recorded at different electrode rotation speeds (400, 600, 900, 1600, and 2500 rpm) by applying the Koutecky–Levich method, as in previous works [ 44 , 50 ].…”

Section: Methodsmentioning

confidence: 99%

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Tailored Porous Carbon Xerogels for Fe-N-C Catalysts in Proton Exchange Membrane Fuel Cells

Álvarez-Manuel,

Alegre,

Sebastián

et al. 2023

Nanomaterials

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Atomically dispersed Fe-N-C catalysts for the oxygen reduction reaction (ORR) have been synthesized with a template-free method using carbon xerogels (CXG) as a porous matrix. The porosity of the CXGs is easily tunable through slight variations in the synthesis procedure. In this work, CXGs are prepared by formaldehyde and resorcinol polymerization, modifying the pH during the process. Materials with a broad range of porous structures are obtained: from non-porous to micro-/meso-/macroporous materials. The porous properties of CXG have a direct effect on Fe-N-CXG activity against ORR in an acidic medium (0.5 M H2SO4). Macropores and wide mesopores are vital to favor the mass transport of reagents to the active sites available in the micropores, while narrower mesopores can generate additional tortuosity. The role of microporosity is investigated by comparing two Fe-N-C catalysts using the same CXG as the matrix but following a different Fe and N doping procedure. In one case, the carbonization of CXG occurs rapidly and simultaneously with Fe and N doping, whereas in the other case it proceeds slowly, under controlled conditions and before the doping process, resulting in the formation of more micropores and active sites and achieving higher activity in a three-electrode cell and a better durability during fuel cell measurements. This work proves the feasibility of the template-free method using CXG as a carbon matrix for Fe-N-C catalysts, with the novelty of the controlled porous properties of the carbon material and its effect on the catalytic activity of the Fe-N-C catalyst. Moreover, the results obtained highlight the importance of the carbon matrix’s porous structure in influencing the activity of Fe-N-C catalysts against ORR.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 86%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Tailored Porous Carbon Xerogels for Fe-N-C Catalysts in Proton Exchange Membrane Fuel Cells

Álvarez-Manuel,

Alegre,

Sebastián

et al. 2023

Nanomaterials

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“…However, after a certain number of cycles, activity decreases due to an excessive removal of iron and the loss of conductivity, as previously reported. [70,71] Therefore, there is an optimal number of AL/TT cycles for each catalyst to maximize its catalytic activity. The number of cycles needed to maximize the activity is not the same for all the catalysts presented in this work, since it depends on the porosity and the surface chemistry of the catalyst.…”

Section: Activity Of Feà Nà Cxg Towards the Oxygen Reduction Reaction...mentioning

confidence: 99%

Effect of Carbon Xerogel Activation on Fe−N−C Catalyst Activity in Fuel Cells

Álvarez‐Manuel,

Alegre,

Sebastián

et al. 2023

ChemElectroChem

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Fe−N−C catalysts are an interesting option for polymer electrolyte fuel cells due to their low cost and high activity towards the oxygen reduction reaction (ORR). Since Fe−N−C active sites are preferentially formed in the micropores of the carbon matrix, increasing the microporosity is highly appealing. In this work, carbon xerogels (CXG) were activated by physical and chemical methods to favor the formation of micropores, used as carbon matrices for Fe−N−C catalysts, and investigated for the ORR. The catalysts were characterized by solid‐state techniques to determine chemical composition and pore structure. Physical activation increased microporosity up to 2‐fold leading to catalysts with a larger density of active sites (more than twice iron and nitrogen uptake, pyridinic N and Nx−Fe). This entailed a higher ORR intrinsic activity determined in a 3‐electrode cell (80 mV better half‐wave potential). At the cathode of a fuel cell, the catalysts based on activated carbon materials showed 26 % lower power density ascribed to a more hydrophilic surface, causing a larger extent of flooding of the electrode that counterbalances the higher intrinsic activity. Interestingly, a more stable behavior was observed for the activated catalysts, with up to 2‐fold better relative power density retention after 20‐hour operation.

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Highly dispersed Zn-N, S co-doped carbon for highly efficient electrocatalytic oxygen reduction

Chang,

Zuo,

et al. 2024

International Journal of Hydrogen Energy

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Organic xerogels combined with iron and nitrogen as PGM-free catalysts for the oxygen reduction reaction

Cited by 4 publications

References 70 publications

Tailored Porous Carbon Xerogels for Fe-N-C Catalysts in Proton Exchange Membrane Fuel Cells

Tailored Porous Carbon Xerogels for Fe-N-C Catalysts in Proton Exchange Membrane Fuel Cells

Effect of Carbon Xerogel Activation on Fe−N−C Catalyst Activity in Fuel Cells

Highly dispersed Zn-N, S co-doped carbon for highly efficient electrocatalytic oxygen reduction

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