Light-Modulated Electronic States of Pd Nanoclusters Stabilized in Ionic Hydrogen-Bonded Frameworks for Enhanced CO2 Photoreduction

Abstract

Modulating the electronic states of active metal sites through microenvironment engineering is a promising strategy for enhancing catalytic performance. However, precise control and stabilization of electronic states present substantial challenges that require further investigation. Herein, an ionic hydrogen-bonded organic framework (HOF) incorporating 2,6-pyridinedicarboxylic acid (PDA) moieties is constructed. The rigid tridentate coordination cores generate a net dipole moment along the metal-nitrogen axis at the metal sites, enabling light-driven modulation of their electronic states through electron density redistribution within the framework. Further investigations reveal that the Pd(II) nanoclusters confined by PDA moieties within the pores of HOF partially formed a stable low-valent species (denoted as Pd^σ+, 0 < σ < 2) upon illumination, promoting efficient separation and migration of photogenerated charge carriers. Consequently, the catalyst exhibited remarkable CO₂ photoreduction performance with a CH₄ evolution rate of 44.3 µmol g⁻¹ h⁻¹ in the presence of H₂O vapor without sacrificial agents, demonstrating both enhanced activity and selectivity. This novel approach modulates the electronic states of metal sites by inducing electron density redistribution through a unique tridentate coordination environment, offering new perspectives for the design of efficient photocatalysts.