**Acknowledgements**

**2.3. Future perspectives in defect engineering for superior electrocatalysis**

100 Graphene Oxide - Applications and Opportunities

low cost, environmental sustainability and high reproducibility.

reactions.

**3. Conclusions**

Immense research work has been done in the field of materials science toward the study of MOFs for highly efficient oxygen electrocatalysis [55]. Basically, MOFs are a class of composite materials with a unique and highly ordered nanoporous (pore sizes smaller than 100 nm) structure, which are designed from a self-assembly of inorganic metals and organic linkers through co-ordination bonds. From an electrochemical aspect, co-ordinated metals could contribute to an electronic effect as a consequence of the changes in platinum electronic structure, directly influencing catalyst activity. Thanks to abundant dual-metal active sites, superior electrocatalysts with ultra-low platinum content could be developed for alcohol electrocatalysis further improving specific activity beyond the conventional platinum alloy approach. Moreover, surface modification of rGO-supported platinum could lead to improved threedimensional nano- (or micro-) structures, resulting in synergistic effects for achieving faster mass and charge transport properties. In this context, proper synthetic procedures based on the controlled carbonization of the organic linkers (primarily containing heteroatoms) might serve as novel rational design strategies for the development of highly porous heteroatomdoped supported catalysts. Also, noteworthy is that such a synthetic method, especially for large-scale production, should meet the requirements for commercialization, which include

Last but not least, another contribution of the metal-organic framework process could be the *in situ* generation of metal oxide nanoparticles and their concomitant dispersion on rGO upon carbonization of the metal-organic complex. Thus, the deposited metal oxide nanoparticles could act as seeds for vacancy generation by etching the carbon─carbon network along the rGO-metal oxide interface. Size-controlled vacancies in the matrix of reduced graphene oxide are not only predicted to break the two-dimensional lattice symmetry, thereby tuning conduction mechanisms, but also act as trapping sites for heteroatom doping [56]. Therefore, in addition, heteroatom-doped porous and open structures on the basal planes together with the metal oxide nanoparticles might serve as novel active sites with high bifunctional activity. Precisely, a bifunctional effect has been associated to the presence of sites that aid in the dissociation of water to form surface hydroxides, which can readily oxidize strongly adsorbed reaction intermediates. Indeed, development of heteroatom-doped size-controlled vacancies could positively contribute toward the improvement of platinum activity in alcohol oxidation

As summarized in this mini-review, an ideal fuel-cell electrode should be porous, and possess high conductivity, accessible electrochemical surface sites, and improved charge and mass transfer pathways. Defect engineering, which involves manipulating the type, concentration, or spatial distribution of heteroatoms and size-controlled vacancies within a solid, along with materials processing approaches, such as three-dimensional structure assembly and surface metal complexation methodologies, has demonstrated its potential to tackle the challenges triggered by energy conversion concerns in direct alcohol fuel cells. With continuous progress on the knowledge The author acknowledges the Brazilian National Council for Scientific and Technological Development (CNPq) for research funding.
