Recent advancements and prospects in noble and non-noble electrocatalysts for materials methanol oxidation reactions

Abstract

The direct methanol fuel cell (DMFC) represents a highly promising alternative power source for small electronics and automobiles due to its low operating temperatures, high efficiency, and energy density. The methanol oxidation process (MOR) constitutes a fundamental chemical reaction occurring at the positive electrode of a DMFC. Pt-based materials serve as widely utilized MOR electrocatalysts in DMFCs. Nevertheless, various challenges, such as sluggish reaction rates, high production costs primarily attributed to the expensive Pt-based catalyst, and the adverse effects of CO poisoning on the Pt catalysts, hinder the commercialization of DMFCs. Consequently, endeavors to identify an alternative catalyst to Pt-based catalysts that mitigate these drawbacks represent a critical focal point of DMFC research. In pursuit of this objective, researchers have developed diverse classes of MOR electrocatalysts, encompassing those derived from noble and non-noble metals. This review paper delves into the fundamental concept of MOR and its operational mechanisms, as well as the latest advancements in electrocatalysts derived from noble and non-noble metals, such as single-atom and molecule catalysts. Moreover, a comprehensive analysis of the constraints and prospects of MOR electrocatalysts, encompassing those based on noble metals and those based on non-noble metals, has been undertaken.

Keywords: Electrocatalytic methanol oxidation reaction; Molecular catalysts; Noble and non-noble catalysts; Single-atom catalysts.

Fig. 1

a The diagram illustrates a typical CH₃OH oxidation reaction, showcasing various reaction intermediates and products. b The diagram illustrates the progressive removal of hydrogen atoms throughout the CH₃OH oxidation process. Adapted with permission [1]. Copyright © 2022, Taylor & Francis

Fig. 2

Depiction of MOR mechanism on the catalyst's surface under a acidic and b basic conditions. Adapted with permission [16]. Copyright © 2019, WILEY–VCH

Fig. 3

a The diagram demonstrates the electrical properties of Pt nanoparticles (Pt NPs) undergo modification by introducing polyanion (PSS) and polycation (PAA, PAH) functional groups, which act as the electron donor–acceptor. b This illustration displays the relationship between the d-band center and the energy required for O₂ adsorption on different Pt slabs. Adapted with permission [39]. Copyright © 2022, Elsevier

Fig. 4

a This picture obtained from a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) shows very thin nanowires made of 22% YO_x/MoO_x-Pt. b Illustration of mass-normalized cyclic voltammograms (CVs) of platinum (Pt). d The study investigates the process of adsorption of CO* and COOH* on surfaces made of pure Pt and Pt surfaces adorned with YO_x (MoO_x). (c–d) The theoretical studies investigated the process of adsorption of *CO and COOH* on surfaces made of pure Pt and Pt surfaces adorned with YO_x(MoO_x). e This diagram illustrates MOR's catalytic process on a YO_x/MoO_x-Pt surface, displaying the energy changes involved. Adapted with permission [40]. Copyright © 2021, Wiley–VCH GmbH. The association between the annealing time and the ordering degree/la ice parameter of Pt₃Mn catalysts is demonstrated in (f). g Investigating the correlation between the specific activity at 0.8 V and the degree of ordering in Pt₃Mn. Adapted with permission [41]. Copyright © 2022, American Chemical Society

Fig. 5

a (i) Preparation protocols, and (ii) MOR pathway for the Pt/rGO–Co₃O₄. Adapted with permission [46]. Copyright @2014, The Royal Society of Chemistry. b (i) CVs, and (ii) Chronoamperometric curves, recorded in 1.0 M KOH + 3.0 M CH₃OH solution, for Co/N-CNFs. Adapted with permission [47]. Copyright © 2015, Elsevier

Fig. 6

a The diagram illustrates the process of creating the NiZn_x@CuO nanoarray structures. The obtained pictures are SEM views of NiZn_x@CuO nanoarray designs. These architectures consist of NiZn alloy sheets with varying thicknesses: b 1000 nm, c 1500 nm, and d 2000 nm. The CVs of the NiZn1000@CuO and brass mesh catalysts in a KOH solution are shown, with and without 0.5 M methanol. The scan rate used was 50 mV s⁻¹. The CVs of the NiZn1000@CuO catalyst in a KOH solution containing methanol concentrations of 0.25 M, 0.50 M, 1.00 M, and 1.50 M. The scan rate used was 50 mV s⁻¹. The CVs of NiZn1000CuO were measured in a 1 M KOH solution containing 0.5 M methanol at different scan rates. h A chronoamperometry experiment was conducted on the NiZn1000@CuO catalyst at a potential of 0.80 V for a duration of 12 h. Adapted with permission [48]. e The CVs of the NiZn1000@CuO and brass mesh catalysts in a KOH solution are shown, with and without 0.5 M methanol. The scan rate used was 50 mV s⁻¹. f The CVs of the NiZn1000@CuO catalyst in a KOH solution containing methanol concentrations of 0.25 M, 0.50 M, 1.00 M, and 1.50 M. The scan rate used was 50 mV s⁻¹. g The CVs of NiZn1000CuO were measured in a 1 M KOH solution containing 0.5 M methanol at different scan rates. Copyrights © 2023, ACS. i–k The graph depicts the comparison between different sample performances in 1 M KOH + 1 M methanol. Adapted with permission [25]. Copyrights© 2024, RSC

Fig. 7

a–d The diagram depicting the TEM images that are recorded at different magnifications for ZnO_(x)CeO_2(1-x) catalyst, e CV, and f Illustration of chronometric curves that are recorded in methanol containing electrolyte, for the prepared catalysts. Adapted with permission [51]. Copyright © 2015, Elsevier. g–j The diagram depicting the TEM images that are recorded at different magnifications for FeNi-based material, g–l Illustration of chronometric curves for the prepared FeNiP-R, and FeNiP-S catalysts. Adapted with permission [52]. Copyrights © 2022, MDPI

Fig. 8

a, b HAADF-STEM images, c CV curves, and d–f Diagram illustrating calculated reaction free energy curves of samples. g CO energy barriers, for the prepared Pt-RuO₂ samples. Adapted with permission [69]. Copyrights © 2021, Springer Nature

Fig. 9

a Graphical illustration showing conversion of Pt islands into single Pt atoms and their promising candidature for MOR. Adapted with permission [73] Copyrights © 2022, Nature. b Diagram depicting reaction pathways for MOR. c Illustration of atomic structures of M@N₄C. d The number of transferred charges from TM atoms to substrate. e Depiction of energy difference between E_f and E_c of M@N₄C. ε_d means the d-band center of transition metal. f Adsorption energies of CH₃OH and H₂O on M@N₄C. g Limiting potentials and corresponding d-band centers for M@N₄C. h Representation of free energy diagrams of Mn@N₄C and Co@N₄C. Adapted with permission [77]. Copyrights © 2023, ACS

Fig. 10

a 3D illustration, b, c CVs for MOR and EOR, d MOR Chronoamperometric curves, and f, g Comparison for the MOR and EOR current density, for the SANi-PtNWs material. h Crystal model for the SANi-decorated Pt (111) surface, displaying various active sites for CO adsorption. Adapted with permission [78]. Copyrights © 2019, Nature Publishing Group

Fig. 11

a Schematic illustration of the process for developing the Ni₃N nanosheet arrays on a nickel foam substrate (Ni₃N NSAs/NF). b Transmission Electron Microscopy (TEM) and c High-Resolution TEM (HR-TEM) pictures of Ni₃N-400 d CV curves of Ni₃N-400 in a 1.0 M KOH solution with and without a 1.0 M methanol solution were obtained using a scanning rate of 50 mV s⁻¹. e The CV curves of Ni₃N at various temperatures and Ni-400 in 1.0 M KOH were obtained using a scanning rate of 50 mV s⁻¹. Adapted with permission [79]. Copyrights © 2023, AIP Publishing

Fig. 12

Mechanism of metal oxo-complexes towards alcohol oxidation. Adapted with permission [82]. Copyright @1989, Elsevier

Fig. 13

Structure of various ligands [84]

Fig. 14

Structure of bpea-pyr and AC ligands [86, 87]

Fig. 15

Chemical structure of a few metal complexes, which were used to catalyze the alcohol oxidation reaction [88]

Fig. 16

Synthesis protocol, and MOR, HER/OER applications of the CoNi-ZIF material. Adapted with permission [93]. Copyrights © 2019, Elsevier

Fig. 17

a Preparation strategy, CVs, b in absence of MeOH, c in presence of MeOH, for NiCo/NiO-CoO/NPCC composites. Adapted with permission [94]. Copyrights © 2019, Elsevier