Fig. 1. Overview of the topics covered in this review.

Fig. 2. Principles of the operation of (a) acid and (b) alkaline based DMFCs.

Fig. 3. (a) Catalysts synthesis Schematic illustration of Pt3Pd1-CeO2/C. (b) Pt3Pd1-CeO2/C, Pt-CeO2/C, and Pt/C MOR performance in 0.1 M HClO4 + 1 M Methanol under the scan rate of 50 mV s-1. (c) MOR mechanism on the Pt3Pd1-CeO2/C catalysts surface. (d) Comparison of ORR polarization curves for Pt3Pd1-CeO2/C and Pt-CeO2/C catalysts with that for 20% Pt/C, in O2-saturated 0.1 M HClO4. (e) Comparison of measured SA and MA at 0.90 V for all corresponding catalysts. (f, g) Schematic illustration of the growth mechanism of PtPd SAANs. (a-e) Reprinted with authorization from Ref. [27]. Copyright (2017) American Chemical Society. (f-g) Reprinted with authorization from Ref. [28]. Copyright (2017), Elsevier.

Fig. 4. (a, b) Pt-Ni-P MNCs SEM and TEM images. (c) ORR polarization curves and Tafel plots of the catalysts in an O2-saturated 0.1 M HClO4 solution at the scan rate of 5 mV s-1 and the rotation rate of 1600 rpm. (d) Mass activities of the MOR for the catalysts recorded in a hybrids of 0.5 M H2SO4 and 1 M CH3OH with a scan rate of 50 mV s-1. (e) Schematic image of the Pt-Ni-P MNCs formation process. (f) Schematic image of the PtBi/C catalysts mechanism. (g) ORR polarization curves of commercial Pt/C and PtBi/C catalysts. (a-e) Reprinted with authorization from Ref. [52]. Copyright (2019) The Royal Society of Chemistry. (f-g) Reprinted with authorization from Ref. [54]. Copyright (2018) American Chemical Society.

Fig. 5. (a) The surface structure diagram of PtIrCo-alloy NPs immersed in Carbon Aerogel matrix. (b) Illustration of the surface structure of PtIrCo-alloy NPs and the preparation procedure of ternary TeCuPt NWs. (a) Reprinted with authorization from Ref. [59]. Copyright (2015), with permission from Elsevier. (b) Reprinted with authorization from Ref. [65]. Copyright (2015) The Royal Society of Chemistry.

Fig. 6. (a) CoAuPd Nanocatalysts Formation Mechanism. (b) Formation mechanism and dealloying process of the CoAuPd nanocatalysts. (a) Reprinted with authorization from Ref. [68]. Copyright (2018) American Chemical Society. (b) Reprinted with authorization from Ref. [69]. Copyright (2019), with permission from Elsevier.

Fig. 7. (a) Schematic diagram of the MoS2QDs@Ti3C2TxQDs@MWCNTs composite formation process as the bifunctional catalyst for ORR and MOR in alkaline solution. (b) Schematic process of constructing the 3D Pt-WN/CNT-rGO catalyst. (a) Reprinted with authorization from Ref. [73]. Copyright (2019), with permission from Elsevier. (b) Reprinted with authorization from Ref. [75]. Copyright (2016), with permission from Springer.