Solvated Electrons at the Diamond-Water Interface: Insights from NV Centers

Solvated electrons in water, the simplest ion in chemistry, have garnered significant interest for their applications in catalysis, biology, and electrosynthesis. Diamond, being chemically inert in aqueous conditions, has been shown to generate solvated electrons with ultraviolet light illumination and subsequent chemical transformations have been confirmed. In this study, we show that near-surface nitrogen vacancy (NV) centers can inject both electrons and holes into ultrapure water at the diamond-water interface through a process of photoionization and charge migration. Using a specially designed diamond membrane-water-electrode cell, we observed photocurrents ranging from tens of femtoamps to picoamps using a bias voltage and green laser excitation. The photocurrent exhibits wavelength-dependent characteristics associated with a charge cycling ionization mechanism and can be modulated by laser power and bias voltage. These findings establish the NV center as a viable source of solvated electrons and potentially expands NV diamond as a substrate for chemical reactions. DFT calculations at the diamond-water interface elucidate the mechanism of charge injection/solvation and reinforce the experimental observations. Future work with the diamond-water interface includes demonstrating in-situ carrier sensing through measurements with the NV centers' T₁ and T₂ times.