Rational Design of Highly Stable and Active MXene‐Based Bifunctional ORR/OER Double‐Atom Catalysts

Abstract

Considering increasing environmental pollution and fossil fuel depletion concerns, renewable energy technologies such as fuel cells, [1] solar cells, [2] Li-ion batteries, [3] and metal-air batteries play an important scientific research role. [4] Rechargeable metal-air batteries [5,6] have received tremendous attention owing to the potential application to replace the mature Li-ion battery, which has nearly reached its theoretical performance limits. [7] Typically, rechargeable metal-air batteries can be divided into two subgroups depending on the electrolyte: water-sensitive systems using organic electrolytes, such as Li-air batteries, which still suffer from organic electrolyte issues where insoluble solid reaction products (Li 2 O or Li 2 O 2 ) block subsequent reactions; [8] and cell systems using aqueous electrolytes, like Zn-air batteries, which are considered as safe and reliable metal-air battery systems. [6] For Designing highly active and bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts has attracted great interest toward metal-air batteries. Herein, an efficient solution to the search for MXene-based bifunctional catalysts is proposed by introducing non-noble metals such as Fe/Co/Ni at the surfaces. These results indicate that the ultrahigh activities in Ni1/Ni2-and Fe1/Ni2-modified MXene-based doubleatom catalysts (DACs) for bifunctional ORR/OER are better than those of well-known unifunctional catalysts with low overpotentials, such as Pt(111) for the ORR and IrO 2 (110) for the OER. Strain can profoundly regulate the catalytic activities of MXene-based DACs, providing a novel pathway for tunable catalytic behavior in flexible MXenes. An electrochemical model, based on density functional theory and theoretical polarization curves, is proposed to reveal the underlying mechanisms, in agreement with experimental results. Electronic structure analyses indicate that the excellent catalytic activities in the MXene-based DACs are attributed to the electroncapturing capability and synergistic interactions between Fe/Co/Ni adsorbents and MXene substrate. These findings not only reveal promising candidates for MXene-based bifunctional ORR/OER catalysts but also provide new theoretical insights into rationally designing noble-metal-free bifunctional DACs.

Rational design of M–N4–Gr/V2C heterostructures as highly active ORR catalysts: a density functional theory study

“… 16 Zhang et al , obtained Ni1/Ni2- and Fe1/Ni2-modified MXene-based double atom catalysts (DACs) as excellent bifunctional ORR/OER catalysts by introducing non-precious metals such as Fe/Co/Ni on the MXene surface through first-principles calculations. 17 Zhou et al , by first-principles calculations for 3d, 4d and 5d transition metal single atoms immobilized on the surface of 2D titanium carbides (Ti 2 CT and Ti 3 C 2 T) as active sites, derived good ORR activity for single-atom Cu-doped Ti 2 CO 2 catalysts with an overpotential of 0.25 V. 18 V 2 C exhibited good performance as a carrier material for catalysts in the ORR.…”

Synergistically enhanced single-atomic site catalysts for clean energy conversion

“…Nevertheless, their atomic resolutions are limited by magnetic lens aberration, and it's difficult to distinguish DACs containing two different metal elements with similar molecular weights due to their close brightness levels in AC HAADF-STEM images. 73 XAS is adopted to conrm metal coordination environments and provide information about oxidation valence, which is generally accepted as a key technique to gain average structural and electronic information at the atomic scale, including bond distance and coordination number. 74 It is worth mentioning that ex situ XAS cannot be used to monitor the dynamic evolution and modication of the oxidation state and coordination environment of active centers during the reaction, while in situ/operando XAS can facilitate an in-depth understanding of the catalytic mechanisms under the operating conditions.…”

Theoretical Inspection of TM-P4C Single-Atom Electrocatalyst: Ultra-High Performance for bifunctional Oxygen Reduction and Evolution Reactions

“…As known, the potential always deviated from the balanced potential to ensure the spontaneous reaction of ORR/OER catalytic process [54], in this work, E is defined to represent the lowest deviated potential. Typically, for ORR process, the 𝐸 𝑂𝑅𝑅 is lower than the standard potential of 1.23 V vs. RHE at 298 K, while the 𝐸 𝑂𝐸𝑅 is higher than that.…”