Hongfei Cheng's research while affiliated with Tongji University and other places

In view of the drawbacks of rechargeable batteries, such as low mass and volumetric energy densities, as well as slow charging rate, proton exchange membrane fuel cells (PEMFCs) are reckoned to be promising alternative devices for energy conversion. Currently, commercial PEMFCs mainly use H 2 as the fuel, but the challenges in generation, storage, and handling of H 2 limit their further development. Among the liquid fuels, formic acid possesses the merits of low flammability, low toxicity, slow crossover rate, faster reaction kinetics, and high volumetric H 2 storage capacity, thus being considered as the most promising energy carrier. It can be used as the energy source for direct formic acid fuel cells (DFAFCs) and formic acid-based H 2 -PEMFCs, which are also called indirect formic acid fuel cells (IFAFCs). A common issue hindering their commercialization is lacking efficient electrocatalysts. In DFAFCs, the anodic electrocatalysts for formic acid oxidation are suffering from stability issue, whereas the cathodic electrocatalysts for oxygen reduction are prone to poisoning by the permeated formic acid. As for IFAFCs, CO and CO 2 impurities generated from formic acid dehydrogenation will cause rapid decay in the catalytic activity. High working temperature can improve the CO and CO 2 tolerance of catalysts but will accelerate catalyst degradation. This review will discuss the mitigation strategies and recent advances from the aspect of electrocatalysts to overcome the above challenges. Finally, some perspectives and future research directions to develop more efficient electrocatalysts will be provided for this promising field.

Direct formic acid fuel cells (DFAFCs) are among the promising energy sources in the future low‐carbon economy. A key challenge hindering their scale‐up and commercialization is the lack of efficient electrocatalysts for anodic formic acid oxidation (FAO). Very recently, the FAO performance of palladium hydrides (PdHx) has been found to be superior to the pristine Pd that is well known for its high intrinsic FAO activity. However, there is enormous space for the controlled synthesis and electrocatalytic behaviors of PdHx‐based nanomaterials awaiting to be explored. Herein, the hydrogen intercalation‐induced crystallization of PdNiP alloy nanoparticles is reported, and the obtained PdNiP‐H nanoparticles exhibit excellent FAO performance. Of particular note, the FAO stability of PdNiP‐H is much better than that of pristine Pd‐H. Furthermore, the PdNiP‐H nanoparticles are used as the anode catalyst in a prototype DFAFC, which demonstrate much higher power density than commercial Pd/C. Density functional theory calculations show that the synergistic effect of alloying Ni and P endows the PdNiP‐H with a higher preference toward FAO via the direct pathway and better anti‐CO* poisoning capability. This work shines new light on the development of PdHx‐based nanoalloys with good activity and stability for DFAFC applications.

Metal-oxygen bonds significantly affect the oxygen reaction kinetics of metal oxide-based catalysts but still face the bottlenecks of limited cognition and insufficient regulation. Herein, we develop a unique strategy to accurately tailor metal-oxygen bond structure via amorphous/crystalline heterojunction realized by ion-exchange. Compared with pristine amorphous CoSnO3-y, iron ion-exchange induced amorphous/crystalline structure strengthens the Sn-O bond, weakens the Co-O bond strength, and introduces additional Fe-O bond, accompanied by abundant cobalt defects and optimal oxygen defects with larger pore structure and specific surface area. The optimization of metal-oxygen bond structure is dominated by the introduction of crystal structure and further promoted by the introduction of Fe-O bond and rich Co defect. Remarkably, the Fe doped amorphous/crystalline catalyst (Co1-xSnO3-y-Fe0.021-A/C) demonstrates excellent oxygen evolution reaction and oxygen reduction reaction activities with a smaller potential gap (ΔE = 0.687 V), and the Zn-air battery based with Co1-xSnO3-y-Fe0.021-A/C exhibits excellent output power density, cycle performance, and flexibility.

The storage and utilization of low‐carbon electricity and decarbonization of transportation are essential components for the future energy transition into a low‐carbon economy. While hydrogen has been identified as a potential energy carrier, the lack of viable technologies for safe and efficient storage and transportation of H2 greatly limits its applications and deployment at scale. Formic acid (FA) is considered one of the promising H2 energy carriers because of its high volumetric H2 storage capacity of 53 g H2/L, and relatively low toxicity and flammability for convenient and low‐cost storage and transportation. FA can be employed to generate electricity either in direct FA fuel cells (FCs) or indirectly as an H2 source for hydrogen FCs. FA can enable large‐scale chemical H2 storage to eliminate energy‐intensive and expensive processes for H2 liquefaction and compression and thus to achieve higher efficiency and broader utilization. This perspective summarizes recent advances in catalyst development for selective dehydrogenation of FA and high‐pressure H2 production. The advantages and limitations of FA‐to‐power options are highlighted. Existing life cycle assessment (LCA) and economic analysis studies are reviewed to discuss the feasibility and future potential of FA as a fuel.