Photo-Piezocatalytic Water Splitting by Post-Synthetic Charge-Transfer Complexation Driven Cluster Modification in Ce-based MOF-808.

Abstract

The production of green H₂ fuel by photocatalytic water splitting has emerged as a potential solution to mitigate challenges related to the energy crisis. The inherent electric field generated within piezoelectric materials under mechanical stress offers a promising avenue for enhancing charge separation in photocatalysis through piezo-phototronic effect. Herein, we develop a photo-piezocatalyst leveraging [Ce₆(µ₃-O)₄(µ₃-OH)₄(HCOO)₆]⁶⁺ cluster modification via post-synthetic multistep integration of a donor-acceptor (D-A) dyad within Ce-based MOF-808 (Ce-MOF). This supramolecular D-A charge transfer (CT) complex inside the confined nanopore of Ce-MOF functions as an efficient light-harvesting unit. Concomitantly, light-mediated electron transfer from the CT complex, results in a mixed valence Ce⁴⁺/Ce³⁺ state  which creates local distortion within the Ce-oxo cluster, transitioning it from an ideal cubic state to a non-centrosymmetric configuration, giving rise to piezoelectric polarization. The synergistic interplay between piezoelectric polarization and enhanced CT driven light-harvesting capabilities culminates in an ultrahigh H₂ production with a rate of 12.7 mmol g^-1h^-1, achieved through overall water splitting under photo-piezocatalytic conditions. This work not only highlights the immense potential of MOFs as efficient catalysts for water splitting but also paves the way for harnessing both solar and mechanical energy through photo-mediated piezocatalytic reactions.