Kinetic study of oxygen reduction reaction on tantalum oxide-based electrocatalysts produced from oxy-tantalum phthalocyanines in acidic media

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: 99%

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

Sebastián

Advanced Energy Materials

et al. 2020

“…While a number of studies has previously reported zirconium oxynitride (Zr 2 ON 2 ) as an promising alternative to platinum based ORR catalysts, [25,26] the reason behind the favourable ORR activity of the same is not well understood. A number of transition metal-based ORR catalysts which show promising ORR activity [25,27,28] also exhibits deviations from standard scaling relations. [29] It is generally accepted that deviation from these scaling relations is the key to enhanced ORR electrocatalysis.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Electronic and Structural Effects in ORR Intermediate Binding on Anion‐Substituted Zirconia Surfaces

Sinha,

Vegge,

Winther

et al. 2024

ChemPhysChem

For oxygen reduction reaction (ORR), the surface adsorption energies of O* and OH* intermediates are key descriptors for catalytic activity. In this work, we investigate anion‐substituted zirconia catalyst surfaces and determine that adsorption energies of O* and OH* intermediates is governed by both structural and electronic effects. When the adsorption energies are not influenced by the structural effects of the catalyst surface, they exhibit a linear correlation with integrated crystal orbital Hamiltonian population (ICOHP) of the adsorbate‐surface bond. The influence of structural effects, due to re‐optimisation slab geometry after adsorption of intermediate species, leads to stronger adsorption of intermediates. Our calculations show that there is a change in the bond order to accommodate the incoming adsorbate species which leads to stronger adsorption when both structural and electronic effects influence the adsorption phenomena. The insights into the catalyst‐adsorbate interactions can guide the design of future ORR catalysts.

“…[7] Thus, the development of non-precious metal catalyst for the oxygen reduction reaction, that would be cheap and effective, has received much attention. [8][9][10][11] Some of the possible alternatives can be catalysts based on transition metal in nitrogen doped graphitic cathodes, [11] oxides and oxynitrides of transition metals e. g. tantalum, [12,13] zirconium oxide based catalysts with multiwalled carbon nanotube (MWCNTs) support [14] and niobium-titanium complex oxides, [15] among others. Exploring the ORR mechanisms on various catalyst surface, and consequently the active sites, using Density Functional Theory (DFT), helps us gain fundamental understanding regarding the same.…”

Section: Introductionmentioning

confidence: 99%

Bending the ORR Scaling Relations on Zirconium Oxynitride for Enhanced Oxygen Electrocatalysis

2023

Technologies like polymer electrolyte membrane fuel cells play an important role in environmentally friendly energy conversion. Essential for their commercialization is the development of cheap and efficient electrocatalyst for the oxygen reduction reaction (ORR). Non-platinum group metal (PGM) based catalysts has exhibited favourable activity in acidic electrolytes. In this study, we computationally explore the catalytic sites on the (111) surface of hydrated zirconium oxynitride using periodic DFT calculations. The thermodynamically limiting step is determined to be the O 2 activation step, (O 2 !OOH*) for the majority of the sites, hence strengthening the OOH* intermediate binding will improve ORR activity. The calculations also reveal that the determined scaling relation for G OH -G OOH (DG OOH ¼ 0:78DG OH þ3.52 eV) is comparable to the standard ORR scaling relation (DG OOH ¼ DG OH þ3.2 eV) however G O* -G OH scaling (DG O* ¼ 1:04DG OH þ2.16 eV) deviates dramatically from the typical ORR scaling relation (DG O* ¼ 2DG OH ).