Vacancy Defect-Rich Perovskite SrTiO₃/Ti₃C₂ Heterostructures In Situ Derived from Ti₃C₂ MXenes with Exceptional Oxygen Catalytic Activity for Advanced Zn–Air Batteries

Abstract

The electrochemical performance enhancement for Zn−air batteries (ZABs) based on a perovskite SrTiO 3 electrocatalyst is seriously obstructed by sluggish oxygen reduction and evolution reaction (ORR/OER) kinetics. Herein, we develop an in situ phase transformation strategy to synthesize Ti 3 C 2 @SrTiO 3 MXene nanocomposites as a bifunctional electrocatalyst for ZABs. The Ti 3 C 2 @SrTiO 3 heterostructures guarantee excellent structural stability and promote interfacial charge transfer to accelerate the electrocatalytic redox kinetics. Ti 3 C 2 MXene not only promotes fast electronic/ionic transfer but also stably anchors SrTiO 3 nanocubes without aggregation to provide abundant catalytic active sites and prominent structural stability. Advantageous oxygen vacancies introduced in SrTiO 3 nanocrystals could effectively regulate the electronic structure of active sites, triggering higher intrinsic electrocatalytic activity. Furthermore, Ti vacancies in the MXene display an important synergetic effect to promote the electron transfer in Ti 3 C 2 @SrTiO 3 heterostructures. Theory calculations reveal that abundant vacancy defects substantially strengthen the oxygen intermediates' adsorption ability on the Ti 3 C 2 @SrTiO 3 catalyst, essentially lowering the energy barrier for the ORR/OER process. As expected, the ZABs based on the Ti 3 C 2 @SrTiO 3 catalyst exhibit exceptional electrochemical performance, an extraordinary open-circuit voltage of 1.44 V, and an essentially improved power density of 122 mW cm −2 . The in situ transformation and defect modulation strategies provide enlightening clues to design a highperformance ZAB cathode catalyst.

Subsurface oxygen reduction reaction activity on Ti2N MXene revealed byin situRaman spectroelectrochemistry

“…The Tafel slopes for benchmark catalysts 10% Pt/C and Ti 3 C 2 are 94.8 mV dec −1 and 108.9 mV dec −1 , respectively, and are in good agreement with reported values from literature. 28,49–52 A Tafel slope close to 120 mV dec −1 suggests that the RDS in the ORR is associated with the first electron transfer. 2 More importantly, Ti 2 N exhibits a different RDS as evidenced by its low Tafel slope of 69.3 mV dec −1 .…”

“…Nevertheless, the lower Tafel slope value of Ti 2 N implies more favorable reaction kinetics. 7,28 Furthermore, the ORR stability of the three catalysts was tested through 4.5 h chronoamperometric measurements (at 0.1 V vs. RHE) and is shown in Fig. 4b.…”

“…8,23,24 With different transition metals, they can exhibit different work functions. 4,8 Among the 30 experimentally synthesized MXenes thus far, 25 most of the works on ORR 2,7,23,[26][27][28] have focused on utilizing Ti 3 C 2 carbide MXene, the rst MXene that was reported in 2011. 25,29,30 This carbide MXene functions well as a cocatalyst capable of increasing the overall electronic conductivity and long-term durability.…”

“…25,29,30 This carbide MXene functions well as a cocatalyst capable of increasing the overall electronic conductivity and long-term durability. 6,7,28 However, nitride MXenes have been predicted to have higher electronic conductivity compared to carbides. [31][32][33][34] Ostadhossein et al theoretically studied the effect of surface termination groups on Ti 4 N 3 MXene to enhance the ORR catalytic activity, and reported substantially lower overpotentials for both -Oand Fterminated Ti 4 N 3 compared to their carbide counterparts.…”

Review and Perspective on Transition Metal Electrocatalysts Toward Carbon-Neutral Energy

“…With a reported durability of over 1000 charge−discharge cycles, the NiCo 2 O 4 /MXenebased liquid Zn-air battery is among the frontrunners of the MXene-based MABs thus far. Hui et al were the first to report MXene/perovskite oxide composites for Zn−air batteries 167. They synthesized vacancy-rich Ti 3 C 2@ SrTiO 3 via in situ phase transformation.…”