Previous studies on scanning electrochemical microscopy (SECM) imaging with nonlocal continuous line probes (CLPs) have demonstrated the ability to increase areal imaging rates by an order of magnitude compared to SECM based on conventional ultramicroelectrode (UME) disk electrodes. Increasing the linear scan speed of the CLP during imaging presents an opportunity to increase imaging rates even further but results in a significant deterioration in image quality due to transport processes in the liquid electrolyte. Here, we show that compressed sensing (CS) postprocessing can be successfully applied to CLP-based SECM measurements to reconstruct images with minimal distortion at probe scan rates greatly exceeding the conventional SECM ″speed limit″. By systematically evaluating the image quality of images generated by adaptable postprocessing CS methods for CLP-SECM data collected at varying scan rates, this work establishes a new upper bound for CLP scan rates. While conventional SECM imaging typically uses probe scan speeds characterized by Péclet numbers (Pe) < 1, this study shows that CS postprocessing methods can allow for an accurate image reconstruction for Pe approaching 5, corresponding to an order of magnitude increase in the maximum probe scan speed. This upper limit corresponds to the onset of chaotic convective flows within the electrolyte for the probes investigated in this work, highlighting the importance of considering hydrodynamics in the design of fast-scanning probes.

Due to the complex nature of probe/substrate interactions in scanning electrochemical microscopy (SECM), SECM has been primarily limited to well-defined probe geometries and slow scan speeds that reduce imaging throughput. Herein, we show thatin situcolorimetric visualization of concentration gradients using pH indicator dyes during SECM measurements can be a powerful tool for understanding the coupled influences of probe geometry and scan speed on the dynamics of localized plumes of electroactive species that mediate probe/substrate interactions. Colorimetric images of plumes generated at a band electrode reveal that probe geometry strongly influences linescan signal distortion and hysteresis at scan speeds surpassing the conventional SECM "speed limit". Combining mechanistic information fromin situcolorimetric imaging with transport models, this article reports design principles that have the potential to enable quantitative SECM with novel probe geometries and at imaging rates that are at least an order of magnitude faster than currently employed.

This article describes a home-built scanning electrochemical microscope capable of achieving high areal imaging rates through the use of continuous line probes (CLPs) and compressed sensing (CS) image reconstruction. The CLP is a nonlocal probe consisting of a band electrode, where the achievable spatial resolution is set by the thickness of the band and the achievable imaging rate is largely determined by its width. A combination of linear and rotational motors allows for CLP scanning at different angles over areas up to 25 cm2 to generate the raw signal necessary to reconstruct the desired electrochemical image using CS signal analysis algorithms. Herein, we provide detailed descriptions of CLP fabrication, microscope design, and the procedures used to carry out scanning electrochemical microscopy imaging with CLPs. In order to illustrate the basic operating procedures for the microscope, line scans and images measured in the substrate generation-probe-collection mode for flat samples containing platinum disk electrodes are presented. These exemplary measurements illustrate methods for calibrating the positioning system, positioning and cleaning the CLP, and verifying proper positioning/probe sensitivity along its length.

In applications of scanning probe microscopy, images are acquired by raster scanning a point probe across a sample. Viewed from the perspective of compressed sensing (CS), this pointwise sampling scheme is inefficient, especially when the target image is structured. While replacing point measurements with delocalized, incoherent measurements has the potential to yield order-of-magnitude improvements in scan time, implementing the delocalized measurements of CS theory is challenging. In this paper we study a partially delocalized probe construction, in which the point probe is replaced with a continuous line, creating a sensor which essentially acquires line integrals of the target image. We show through simulations, rudimentary theoretical analysis, and experiments, that these line measurements can image sparse samples far more efficiently than traditional point measurements, provided the local features in the sample are enough separated. Despite this promise, practical reconstruction from line measurements poses additional difficulties: the measurements are partially coherent, and real measurements exhibit nonidealities. We show how to overcome these limitations using natural strategies (reweighting to cope with coherence, blind calibration for nonidealities), culminating in an end-to-end demonstration.

Oxygen (O2) and hydrogen (H2) gas bubbles are the desired products from photoelectrochemical water splitting, but they are also a common source of efficiency losses in photoelectrochemical cells (PECs) that are poorly understood and often difficult to quantify. When attached to the surface of a photoelectrode, a gas bubble can induce optical, kinetic, ohmic, and mass-transport losses. The operating conditions and dynamic behavior that underlie these bubble-induced losses are complex and convoluted, but understanding these dynamics would be invaluable for selecting operating conditions and engineering photoelectrode surfaces to minimize those losses. Toward this end, we employ in situ scanning photocurrent microscopy (SPCM) to investigate the local photocurrent losses associated with isolated H2 bubbles attached to the surface of a photoelectrode. For the first time, we are able to quantify and resolve local bubble-induced photocurrent losses on a photoelectrode at the sub-bubble level. As a basis for this...

This study investigates the use of membraneless electrolyzers based on angled mesh flow-through electrodes for the simultaneous production of acid and base (lye) from aqueous brine solutions. These electrolyte-agnostic flow cells are capable of producing a wide variety of acids and bases with precisely controlled pH using a simple cell design.

Photoelectrochemical cells (PECs) are integrated devices that offer an attractive approach to converting solar energy into storable chemical energy, such as hydrogen. In PEC-driven water electrolysis, the product species, hydrogen and oxygen, are first evolved as gas bubbles at the surface of the electrode. However, these gas bubbles can lead to significant efficiency losses, due to increasing electrode surface coverage by gas bubbles that block active material and reactants from reaching the photoelectrode surface. It is known that when gas bubbles are attached to the surface of a photoelectrode, they can induce a variety of loss mechanisms, however, these bubble losses are difficult to quantifiably measure and still not completely understood. Therefore, it is desirable to study the gas evolution dynamics on these photoelectrodes so that systems can be designed to minimize efficiency losses. In this study, in situ scanning photocurrent microscopy (SPCM) is used, for the first time, to investigate the local photocurrent losses associated with isolated hydrogen bubbles attached to the surface of a photoelectrode. By measuring the change in photocurrent response of an area of interest, we can quantify and determine local optical bubble-induced photocurrent losses on a photoelectrode at the sub-bubble level. Silicon-based photocathodes based on a metal-insulator-semiconductor (MIS) architecture containing a continuous 3 nm metal layer, are used for this work. SPCM is used to systematically investigate the influence of varying bubble size on the performance of these photoelectrodes under varied experimental conditions. The quantitative SPCM measurements are combined with optical modeling based on Snell’s Law. Comparisons between the experimentally determined losses and those predicted with the optical model are used to elucidate relationships between local photocurrent losses and bubble size. Significant increases in optical losses for larger bubbles (diameter > 150 μm) are seen, due to regions of total internal reflection that are not present for the small bubbles studied. Finally, the knowledge gained from the SPCM single-bubble measurements are applied to a large photoelectrode surface under uniform AM1.5 illumination. Using these measurements, we can model the current-time profile associated with multiple bubble evolution off of a fully-illuminated photoelectrode surface. Overall, this study sets the stage for quantitatively modeling bubble-related losses for various photoelectrode geometries and operating conditions. We have also provided valuable insight into the optical losses associated with having a single surface bound gas bubbles on a photoelectrode surface.