Dra. Elgueta-Herrera, Elizabeth

This review provides an overview of recent advancements in cathode materials for proton exchange membrane fuel cells (PEMFCs), focusing on their role in catalyzing the oxygen reduction reaction (ORR). This begins with a fundamental discussion of the ORR mechanism, including two‐electron and four‐electron pathways. The review then explores a wide range of electrocatalyst materials, starting with precious metal catalysts, particularly platinum‐based materials, along with alloying strategies and composite structures. This then delves into nonprecious metal catalysts, encompassing metal‐free ORR electrocatalysts, carbon‐supported composite materials (including heteroatom doping and metal‐carbon composites), and transition metal oxides. The review further examines metal phthalocyanines, biomass‐derived catalysts, bimetallic and trimetallic nanoparticles supported on carbon matrices, and chalcogenides (oxides, sulfides, and selenides) as ORR electrocatalysts. Advanced materials such as single‐ and dual‐atom catalysts, high‐entropy alloys, and metal organic frameworks derived electrocatalysts are also discussed. We analyze the identification of reaction sites and the effect of structure on catalytic activity. Furthermore, the review covers electrochemical measurements in PEMFCs and explores technological applications and industrial relevance, including products and patents. Finally, this review concludes by addressing future perspectives and challenges in the field of cathode materials for PEMFCs.

The adsorption capacity of hydrogels derived from modified xylan hemicellulose has been tested in order to develop new bio-based adsorbent materials useful for removing metal ions pollutants, such as Cd(II), Cu(II) and Pb(II) from an aqueous solution. Xylan was extracted from bleached kraft pulp of eucalyptus and subsequently modified with different proportions of functional sulfonic acid groups (HA3–HA7) and sulfonate groups (HS30–HS70) to generate hydrogels. The results showed that all the synthesized hydrogels were capable of adsorbing metal ions, being the hydrogels with 30% and 50% xylan the ones that presented the highest adsorption capacity. Maximum capacity studies at different initial concentrations revealed that at an initial concentration of 300 mg·L−1, the HA3 hydrogel presented an adsorption capacity of 193 mg Pb(II), 182 mg Cd(II), and 66 mg Cu(II) per g hydrogel. The HA5 hydrogel presented a capacity of 185 mg Pb(II), 113 mg Cd(II), and 48 mg Cu(II) per g hydrogel. The HS30 hydrogel exhibited an adsorption of 205 mg Pb(II), 174 mg Cd(II), and 71 mg Cu(II) per g hydrogel, and HS50 hydrogel exhibited an adsorption capacity of 273 mg Pb(II), 143 mg Cd(II), and 45 mg Cu(II) per g hydrogel. These results show that modified Xylan hemicellulose is a promising adsorbent for removal Cd(II), Cu(II), and Pb(II) ions from aqueous solutions.