Reducing the platinum amount in fuel cells while securing catalytic performance would reduce associated costs. Therefore, our recently published strategy, targeting nanostructured Pt catalysts, combines atom-precise Pt nanoclusters (NCs) and metal-organic frameworks (MOFs) as porous, crystalline and stabilizing matrixes, to fabricate Pt12±x@MOFs. The activated PtNCs are released out of the scaffold via a controlled digestion of the MOF onto a support yielding Pt nanoparticles (NPs) with a narrow size distribution and an exceptional mass activity in the electrochemical oxygen reduction reaction (ORR). Moreover, including a non-noble metal can tremendously improve the catalytic activity in the ORR as previously shown for Pt3M (M = Co, Ni) alloys. Here, this bottle-around-ship approach – embedding preformed species into a MOF matrix – is expanded to more than six clusters studying different sized Pt as well as heterometallic compounds, [Ptx(CO)y]z-and [Ptx1Mx2(CO)y]z- (M = Co, Ni). Our results highlight a direct correlation between cluster size and charge and its spatial location within a ZIF-8 matrix. Most NCs with similar properties as [Pt9(CO)18]2- behave likewise while more fragile and bigger analogues are difficult to encapsulate unspoiltly and homogeniously within the ZIF-8 crystal. High resolution electron microscopy with elemental mapping is used to monitor the cluster integrity and location within the MOF during the ligand-stripping process. Furthermore, the templating properties of ZIF-8 are investigated by fine-tuning the releasing procedure of the activated NCs and generate mono- and bimetallic NPs with a narrow size-distribution. Thereby, the NP size is not only dependent on the initial cluster size but intrinsic forces are important. These results were correlated to preliminary catalytic ORR activity data evaluated by rotating disk electrode experiments.

Atom-precise nanoclusters encapsulated in metal-organic frameworks for electrocatalytic applications

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.