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Page 10 of 31 Chen et al. Microstructures 2023;3:2023025 https://dx.doi.org/10.20517/microstructures.2023.12

Table 1. Comparison between SMSI and novel construction strategies
SMSI O-SMSI A-SMSI wcSMSI R-SMSI L-SMSI
Metal VIII group VIII/IB group metals VIII/IB group VIII/IB group VIII/IB group metals VIII group
metals metals metals metals
Support Reducible metal Hydroxyapatite, Reducible metal TiO 2 LDO, MoO , MgO, TiO , CeO 2
3
2
oxide phosphate, and ZnO oxide BaO, Mn O
2 3
3+
Condition H 2 O 2 CO -H , H /H O Ti treatment N , CO , CH /He Laser
2
4
2
2
2
2
2
/CH OH/N 2 treatment
3
temperature High- High-temperature > 200 °C Room- High-temperature Room-
temperature temperature temperature
Electronic transfer Support to metal Metal to support Support to metal Support to Support to metal Support to
metal metal
Suppression of small Yes Yes Yes Yes Yes Yes
molecule
adsorption
classical SMSI, such as a wide scope of supports, various construction atmospheres, low heating
temperatures, and excellent stability under harsh reaction conditions.
APPLICATION OF STRONG METAL-SUPPORT INTERACTIONS IN ORR
In general, the requirement for an ideal ORR catalyst includes both high activity and stability. A series of
classical SMSI systems, including SMSI, O-SMSI, and A-SMSI catalysis, precisely satisfy the high stability
requirement for ORR due to their inherent encapsulation effect. In addition, the electron and mass transfer
between metal and support makes the modulation of the catalyst activity more feasible and efficient. For
some new types of SMSI, i.e., L-SMSI, wcSMSI, and R-SMSI, their low or room temperature construction
strategy and independent encapsulation phenomena can effectively disperse the metal and prevent its
detachment and agglomeration, greatly improving the stability of the catalyst.

Oxide-based materials
TMOs are an ideal alternative to carbonaceous materials as supports for Pt NPs not only because of their
robust corrosion resistance but also the strong interaction with the Pt NPs inducing the SMSI effect for
enhanced ORR activity and stability enhancement . The SMSI effect mainly arises from an interfacial
[67]
interaction of Pt-Metal Oxide (Pt-MO), which leads to a modification of the Pt electronic structure and
provides several advantages for ORR, including (1) facilitating the O adsorption and O-O bond cleavage on
2
the Pt surface; (2) decreasing the OH coverage on the Pt surface; and (3) preventing the detachment and
further aggregation of Pt NPs. Based on this, a variety of TMOs have been applied to support Pt-based
catalysts toward ORR, such as titanium oxide, cerium oxide, and tungsten oxide.

Titanium oxide (TiO )
2
Among the various metal oxide supports reported so far, titanium oxide-based materials have been
considered as a promising support for nanosized catalysts in the ORR owing to their low cost, nontoxicity,
high defect contents, etc. [68-70] . The robust corrosion resistance ensures TiO is an intrinsically stable
2
electrode material under harsh operation conditions, especially in acid medium and high-temperature
environments. Most importantly, the synergetic effect of SMSI between Pt NPs and TiO can exquisitely
2
enhance the electrocatalytic performance of Pt NPs and the durability of the catalysts. However, as a
support, TiO has several drawbacks, such as low electrical conductivity (10 Scm ) and poor reactivity,
-1
-8
2
limiting the electron interactions between Pt and Ti atoms . Therefore, the issue of insufficient
[71]
conductivity of TiO should be primarily resolved before the application of TiO to improve the
2
2
performance and stability of Pt-based catalysts for ORR.