**4. Conclusion**

We have presented various techniques to obtain novel catalysts that successfully enhance the efficiency and productivity of PET glycolysis for monomer recycling as well as the performance of polymer electrolyte membrane fuel cells. The catalysts can be considered a practical solution that addresses various issues in these processes, such as catalyst separability, reusability, and performance in limited operating conditions. The use of ultrasound-assisted synthesis provided an efficient alternative synthesis approach to obtain metal-oxide composites of silica and graphene oxide under mild conditions. The use of these catalyst composites offers the potential of industrial-scale use given their high activity in addition to thermal and chemical stability. Another practical and effective approach is the use of a magnetically recoverable catalyst, γ-Fe2O3. The superparamagnetic nanocatalyst, offering comparable performance and stability as the other solid catalysts, has further advantages of efficient separation and relatively simplicity of synthesis approach. For fuel cell development, we developed a nontoxic and easy chemical method to fabricate Pt and dopamine-induced carbon@silica compo‐ site without complex apparatus. The silica nanoparticles as support material acted as a selfhumidifying material, while the dopamine coating played the role of a self-reducing agent and adhesive layer for anchoring the Pt nanoparticles. Additionally, the N-doped carbon from carbonization of dopamine coating enhanced electrical conductivity of the composite. This resulted to overall superior performance of the composite as anode catalyst even under low humidity conditions. The fabrication methods and alternative catalysis strategies presented will be valuable for the commercialization of green catalysts for PET monomer recycling and energy conversion systems.
