Tantalum-based electrocatalysts prepared by a microemulsion method for the oxygen reduction and evolution reactions

Sebastián

Advanced Energy Materials

et al. 2020

and storage devices, such as fuel cells and metal-air batteries. [1][2][3][4][5][6][7][8] Especially, the polymer electrolyte membrane fuel cells, used in automotive applications, have already achieved the level of commercialization. [5] Although the Pt group metal (PGM) catalysts can efficiently address the kinetics-related challenges, the high cost and the limited resource of PGM greatly hinder the widespread commercialization of these energy conversion and storage devices. Therefore, the development of low-cost, highly active, and stable PGM-free catalysts, to replace the PGM ones, toward ORR, is highly desired. Over the past decades, extensive research was devoted to the development of alternative and low-cost catalysts, including i) non-precious Fe and Co-based metal catalysts, [3,4,[9][10][11] ii) metal oxides, nitrides, and oxynitrides, [12][13][14] and iii) metal-free catalysts such as carbon-based materials. [15] Oxides from metals belonging to groups 4 and 5 (Ti, V, Zr, Nb, Hf, Ta) have attracted interest in these fields, mainly due to their low cost compared to PGM catalysts, environmental compatibility, and excellent stability in acid medium. [12,[16][17][18][19] It has been demonstrated that these oxides can have some activity toward ORR, if their stoichiometry is conveniently tailored to generate a high concentration The oxygen reduction reaction (ORR) is one of the most important reactions in renewable energy conversion and storage devices. The full deployment of these devices depends on the development of highly active, stable, and low-cost catalysts. Herein, a new hybrid material consisting of Na 2 Ta 8 O 21−x / Ta 2 O 5 /Ta 3 N 5 nanocrystals grown on N-doped reduced graphene oxide is reported. This catalyst shows a significantly enhanced ORR activity by ≈4 orders of magnitude in acidic media and by ≈2 orders of magnitude in alkaline media compared to individual Na 2 Ta 8 O 21−x on graphene. Moreover, it has excellent stability in both acid and alkaline media. It also has much better methanol tolerance than the commercial Pt/C, which is relevant to methanol fuel cells. The high ORR activity arises not only from the synergistic effect among the three Ta phases, but also from the concomitant nitrogen doping of the reduced graphene oxide nanosheets. A correlation between ORR activity and nitrogen content is demonstrated. Deep insights into the mechanism of the synergistic effect among these three Ta-based phases, which boosts the ORR's kinetics, are acquired by combining specific experiments and density functional theory calculations.

Section: Resultsmentioning

confidence: 94%

2 O_{2} + 4 H^{+} + 4 e^{-} \to 2 H_{2} O E^{0} = 1.23 V versus RHE

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Section: Introductionmentioning

confidence: 99%

Engineering of a Low‐Cost, Highly Active, and Durable Tantalate–Graphene Hybrid Electrocatalyst for Oxygen Reduction

Sebastián

Advanced Energy Materials

et al. 2020

“…Recently, group 4 or 5 based transition metal oxides have emerged as new candidate materials. They are cost‐effective and stable under ORR operating conditions [25–30] . However, their ORR catalytic activity and electrical conductivity need to be improved to become more suitable for practical applications as alternatives to Pt‐based catalysts.…”

Section: Introductionmentioning

confidence: 99%

Enhancing Oxygen Reduction Reaction Activity Using Single Atom Catalyst Supported on Tantalum Pentoxide

2022

Transition metal oxides have emerged as promising costeffective alternatives to Pt catalysts for oxygen reduction reaction (ORR) in fuel cell applications. However, their low stability under harsh electrochemical conditions hinders their widespread applications. Tantalum pentoxide (Ta 2 O 5 ) has proven to be a stable material under ORR conditions, but its activity is limited. In this work, we incorporate single atom catalysts (SACs) in Ta 2 O 5 to resolve the limited ORR activity of this material by altering the electronic structures of surface Ta atoms. We use density functional theory (DFT) calculations to identify the most promising SACs with enhanced ORR activity. Pt, Rh, and Ir, are found to be the most promising SACs with improved ORR activity and high stability. This work suggests that SACs are effective in enhancing Ta 2 O 5 catalytic activities for ORR.

“… 4 In the past few years, several studies have demonstrated that transition metals combined with carbon materials can be employed as good bifunctional catalysts, showing good catalytic performance for both reactions and stability in alkaline media. 9 − 13 …”

Section: Introductionmentioning

confidence: 99%

Titanium Dioxide/N-Doped Graphene Composites as Non-Noble Bifunctional Oxygen Electrocatalysts

Luque-Centeno

Martı́nez-Huerta

Sebastián

et al. 2021

Ind. Eng. Chem. Res.

Bifunctional oxygen electrocatalysts are essential in the development of low-temperature unitized regenerative fuel cells (URFCs), as a promising alternative for storing energy via hydrogen. TiO 2 , as a semiconductor material, is commonly not established as an active electrocatalyst for oxygen reduction and oxygen evolution due to its poor electrical conductivity and low reactivity. Here, we demonstrated that composites composed of TiO 2 and N-doped graphene can be active in oxygen reduction and evolution reactions in an alkaline environment. Combination factors such anatase/rutile interaction, N-doping graphene, and the presence of Ti 3+ /Ti–N species raise the active sites and improve the electrochemical activity. Our results may afford an opportunity to develop a non-noble and promising electrocatalyst in energy storage technology.