Operando NMR spectroscopic analysis of proton transfer in heterogeneous photocatalytic reactions

Abstract

Proton transfer (PT) processes in solid–liquid phases play central roles throughout chemistry, biology and materials science. Identification of PT routes deep into the realistic catalytic process is experimentally challenging, thus leaving a gap in our understanding. Here we demonstrate an approach using operando nuclear magnetic resonance (NMR) spectroscopy that allows to quantitatively describe the complex species dynamics of generated H2/HD gases and liquid intermediates in pmol resolution during photocatalytic hydrogen evolution reaction (HER). In this system, the effective protons for HER are mainly from H2O, and CH3OH evidently serves as an outstanding sacrificial agent reacting with holes, further supported by our density functional theory calculations. This results rule out controversy about the complicated proton sources for HER. The operando NMR method provides a direct molecular-level insight with the methodology offering exciting possibilities for the quantitative studies of mechanisms of proton-involved catalytic reactions in solid–liquid phases.

Perylenetetracarboxylic acid nanosheets with internal electric fields and anisotropic charge migration for photocatalytic hydrogen evolution

“…6c ), indicating that the origin of H 2 is aqueous protons 82 . The presence of the H/D isotope effect decreases the photocatalytic HER 83 , but in principle, it does not harm our inferences about the source of H 2 in the reaction systems. To rule out the possibility that the protons were from hole scavengers (ascorbic acid, AA), the high-resolution mass spectra of the solution before and after the HER were applied.…”

Proton-assisted electron transfer and hydrogen-atom diffusion in a model system for photocatalytic hydrogen production

“…For another, proton transfer and proton-assisted electron transfer play a key role in determining specific reaction pathways and photocatalytic efficiencies [9][10][11] , but there is no consensus on the mechanism of dynamic interfacial proton transfer. Previous studies have reported that molecularly adsorbed water or methanol can mediate the long-range proton transport on active photocatalytic surfaces [12][13][14][15] .…”

Qualitative Approaches Towards Useful Photocatalytic Materials

“…Access to synchrotron techniques is still restricted, and the use of specialized equipment and purpose-built instrumentation is not universally accessible. Progress has been made toward developing lab-based in situ / operando approaches for the analysis of photocatalytic materials using, for instance, advanced laser techniques (Pastor et al, 2017 ) or in situ nuclear magnetic resonance (Wang et al, 2016 ). Even as core techniques applied ex situ , qualitative measures must be considered, since an inadequate analysis based on these techniques is still a source of frustration and controversy in the literature.…”