Advanced 3D ordered electrodes for PEMFC applications: From structural features and fabrication methods to the controllable design of catalyst layers

The catalyst layers(CLs) electrode is the key component of the membrane electrode assembly(MEA) in proton exchange membrane fuel cells(PEMFCs). Conventional electrodes for PEMFCs are composed of carbon-supported, ionomer, and Pt nanoparticles, all immersed together and sprayed with a micron-level thickness of CLs. They have a performance trade-off where increasing the Pt loading leads to higher performance of abundant triple-phase boundary areas but increases the electrode cost. Major challenges must be overcome before realizing its wide commercialization. Literature research revealed that it is impossible to achieve performance and durability targets with only high-performance catalysts, so the controllable design of CLs architecture in MEAs for PEMFCs must now be the top priority to meet industry goals. From this perspective, a 3D ordered electrode circumvents this issue with a support-free architecture and ultrathin thickness while reducing noble metal Pt loadings. Herein, we discuss the motivation in-depth and summarize the necessary CLs structural features for designing ultralow Pt loading electrodes. Critical issues that remain in progress for 3D ordered CLs must be studied and characterized. Furthermore, approaches for 3D ordered CLs architecture electrode development, involving material design, structure optimization, preparation technology, and characterization techniques, are summarized and are expected to be next-generation CLs for PEMFCs. Finally, the review concludes with perspectives on possible research directions of CL architecture to address the significant challenges in the future.

Constructing extrinsic oxygen vacancy on the surface of photocatalyst as CO_(2)and electrons reservoirs to improve photocatalytic CO_(2)reduction activity

Constructing own oxygen vacancies in the photocatalysts is a very promising method to improve their photocatalytic CO_(2)reduction activity.However,some catalysts have excellent stabilities,making it difficult for them to construct their own oxygen vacancies.To simplify the above difficulty of stable photocatalysts,constructing extrinsic oxygen vacancies on their surface as a novel idea is proposed.Here,a stable TiO_(2)nanosheet is chosen as a research object,we uniformly deposited BiOCl quantum dots on their surface via a simple adsorption-deposition method.It is found that BiOCl quantum dots are able to simultaneously self-transform into defective BiOCl with many oxygen vacancies when the photocatalyst is performed photocatalytic CO_(2)reduction.These extrinsic oxygen vacancies can act as“CO_(2)and photo-generated electrons reservoirs”to improve CO_(2)capture and accelerate the separation of photogenerated electrons and holes.For the above reasons,the modified TiO_(2)showed obvious enhancement of photocatalytic CO_(2)reduction compared to pristine TiO_(2)and BiOCl.This work may open a new avenue to broaden the use of oxygen vacancies in the process of photocatalytic CO_(2)reduction.

Enhancing photocatalytic CO_(2)reduction with TiO_(2)-based materials:Strategies,mechanisms,challenges,and perspectives

The concentration of atmospheric CO_(2)has exceeded 400 ppm,surpassing its natural variability and raising concerns about uncontrollable shifts in the carbon cycle,leading to significant climate and environmental impacts.A promising method to balance carbon levels and mitigate atmospheric CO_(2)rise is through photocatalytic CO_(2)reduction.Titanium dioxide(TiO_(2)),renowned for its affordability,stability,availability,and eco-friendliness,stands out as an exemplary catalyst in photocatalytic CO_(2)reduction.Various strategies have been proposed to modify TiO_(2)for photocatalytic CO_(2)reduction and improve catalytic activity and product selectivity.However,few studies have systematically summarized these strategies and analyzed their advantages,disadvantages,and current progress.Here,we comprehensively review recent advancements in TiO_(2)engineering,focusing on crystal engineering,interface design,and reactive site construction to enhance photocatalytic efficiency and product selectivity.We discuss how modifications in TiO_(2)'s optical characteristics,carrier migration,and active site design have led to varied and selective CO_(2)reduction products.These enhancements are thoroughly analyzed through experimental data and theoretical calculations.Additionally,we identify current challenges and suggest future research directions,emphasizing the role of TiO_(2)-based materials in understanding photocatalytic CO_(2)reduction mechanisms and in designing effective catalysts.This review is expected to contribute to the global pursuit of carbon neutrality by providing foundational insights into the mechanisms of photocatalytic CO_(2)reduction with TiO_(2)-based materials and guiding the development of efficient photocatalysts.