Defect-modulated ionic friction at hBN/water interfaces

Charge transport at solid/liquid interfaces is vital to energy conversion, electrochemistry, and biological activities. These buried interfaces are the locus where continuum approaches break down, and molecular details become of utmost importance, with traditional ensemble-averaged studies giving an incomplete picture of the dynamics. Here, we build upon recently developed single-molecule microscopy optofluidic platform, to investigate the statistics of single charge transport at aqueous hexagonal Boron Nitride interfaces, demonstrating the microscopic origin of its non-Gaussian character and the control of transport by irradiation-induced surface defects. By increasing irradiation of the hBN crystals, we modulate the morphological distribution of adsorption sites, leading to a slow-down of interfacial charge transport, akin to an increasing frictional interaction. Charge hopping displacements feature exponentially-decaying arms, strongly departing from Gaussian distributions. 2D Brownian dynamics simulations evidence that these exponential tails originate from molecular jumps between trapping sites, allowing a consistent match between statistical distributions and the effective diffusion coefficient. Our study highlights the key yet overlooked role of defects in regulating interfacial charge transport, with relevance for energy applications. Charge transport at solid/liquid interfaces is crucial for the energy realm, yet traditional methods fail to capture the underlying molecular processes. Here, a single-molecule microscopy optofluidic platform reveals how surface defects modulate charge dynamics and lead to anomalous transport.