The commercialization of fuel cells, such as proton exchange membrane fuel cells and direct methanol/formic acid fuel cells, is hampered by their poor stability, high cost, fuel crossover, and the sluggish kinetics of platinum (Pt) and Pt-based electrocatalysts for both the cathodic oxygen reduction reaction (ORR) and the anodic hydrogen oxidation reaction (HOR) or small molecule oxidation reaction (SMOR). Thus far, the exploitation of active and stable electrocatalysts has been the most promising strategy to improve the performance of fuel cells. Accordingly, increasing attention is being devoted to modulating the surface/interface electronic structure of electrocatalysts and optimizing the adsorption energy of intermediate species by defect engineering to enhance their catalytic performance. Defect engineering is introduced in terms of defect definition, classification, characterization, construction, and understanding. Subsequently, the latest advances in defective electrocatalysts for ORR and HOR/SMOR in fuel cells are scientifically and systematically summarized. Furthermore, the structure-activity relationships between defect engineering and electrocatalytic ability are further illustrated by coupling experimental results and theoretical calculations. With a deeper understanding of these complex relationships, the integration of defective electrocatalysts into single fuel-cell systems is also discussed. Finally, the potential challenges and prospects of defective electrocatalysts are further proposed, covering controllable preparation, in situ characterization, and commercial applications.

Defect Engineering for Fuel‐Cell Electrocatalysts

Nanozymes have attracted extensive interest owing to their high stability, low cost and easy preparation, especially in the field of cancer therapy. However, the relatively low catalytic activity of nanozymes in the tumor microenvironment (TME) has limited their applications. Herein, we report a novel nanozyme (PtFe@Fe3 O4 ) with dual enzyme-like activities for highly efficient tumor catalytic therapy. PtFe@Fe3 O4 shows the intrinsic photothermal effect as well as photo-enhanced peroxidase-like and catalase-like activities in the acidic TME, thereby effectively killing tumor cells and overcoming the tumor hypoxia. Importantly, a possible photo-enhanced synergistic catalytic mechanism of PtFe@Fe3 O4 was first disclosed. We believe that this work will advance the development of nanozymes in tumor catalytic therapy.

A Nanozyme with Photo-Enhanced Dual Enzyme-Like Activities for Deep Pancreatic Cancer Therapy

Single-atom catalysts (SACs) have sparked broad interest recently while the low metal loading poses a big challenge for further applications. Herein, a dual protection strategy has been developed to give high-content SACs by nanocasting SiO2 into porphyrinic metal–organic frameworks (MOFs). The pyrolysis of SiO2@MOF composite affords single-atom Fe implanted N-doped porous carbon (FeSA–N–C) with high Fe loading (3.46 wt%). The spatial isolation of Fe atoms centered in porphyrin linkers of MOF sets the first protective barrier to inhibit the Fe agglomeration during pyrolysis. The SiO2 in MOF provides additional protection by creating thermally stable FeN4/SiO2 interfaces. Thanks to the high-density FeSA sites, FeSA–N–C demonstrates excellent oxygen reduction performance in both alkaline and acidic medias. Meanwhile, FeSA–N–C also exhibits encouraging performance in proton exchange membrane fuel cell, demonstrating great potential for practical application. More far-reaching, this work grants a general synthetic methodology toward high-content SACs (such as FeSA, CoSA, NiSA). Single-atom catalysts (SACs) with high metal loading are highly desired to improve catalytic performance. Here, the authors report a dual protection strategy by nanocasting SiO2 into metal–organic frameworks to prepare high-loading SACs with excellent catalytic performance toward oxygen reduction.

/pdf/nanocasting-sio-2-into-metal-organic-frameworks-imparts-dual-3zgbdcoqlm.pdf

Nanocasting SiO 2 into metal–organic frameworks imparts dual protection to high-loading Fe single-atom electrocatalysts

Precise control over the size, shape, composition, structure, and crystal phase of random alloy and intermetallic nanocrystals has been intensively explored in technologically important application...

Noble-Metal Based Random Alloy and Intermetallic Nanocrystals: Syntheses and Applications.

In the face of the global energy challenge and progressing global climate change, renewable energy systems and components, such as fuel cells and electrolyzers, which close the energetic oxygen and carbon cycles, have become a technology development priority. The electrochemical oxygen reduction reaction (ORR) and the direct electrochemical carbon dioxide reduction reaction (CO2 RR) are important electrocatalytic processes that proceed at gas diffusion electrodes of hydrogen fuel cells and CO2 electrolyzers, respectively. However, their low catalytic activity (voltage efficiency), limited long-term stability, and moderate product selectivity (related to their Faradaic efficiency) have remained challenges. To address these, suitable catalysts are required. This review addresses the current state of research on Pt-based and Cu-based nanoalloy electrocatalysts for ORR and CO2 RR, respectively, and critically compares and contrasts key performance parameters such as activity, selectivity, and durability. In particular, Pt nanoparticles alloyed with transition metals, post-transition metals and lanthanides, are discussed, as well as the material characterization and their performance for the ORR. Then, bimetallic Cu nanoalloy catalysts are reviewed and organized according to their main reaction product generated by the second metal. This review concludes with a perspective on nanoalloy catalysts for the ORR and the CO2 RR, and proposes future research directions.

Alloy Nanocatalysts for the Electrochemical Oxygen Reduction (ORR) and the Direct Electrochemical Carbon Dioxide Reduction Reaction (CO2 RR).

A space-confined interfacial conversion approach is developed to directly transform 3 nm solid Pt nanoparticles into a 5 nm hollow PtFe alloy featuring a Pt-skin surface. The approach presented for the structural evolution from solid Pt NPs to hollow PtFe alloy with controlled size, structure, and composition can be applied to other multimetallic electrocatalysts.

Structural Evolution of Solid Pt Nanoparticles to a Hollow PtFe Alloy with a Pt-Skin Surface via Space-Confined Pyrolysis and the Nanoscale Kirkendall Effect

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Structural Evolution of Solid Pt Nanoparticles to a Hollow PtFe Alloy with a Pt-Skin Surface via Space-Confined Pyrolysis and the Nanoscale Kirkendall Effect