Silicon (Si) is broadly used in electrochemical and photoelectrochemical devices, where the capacitive and Faradaic reactions at the Si/water interfaces are critical for signal transduction or noise generation. However, probing the electrified Si/water interface at the microscopic level remains a challenging task. Here we focus on hydrogenated Si surfaces in contact with water, relevant to transient electronics and photoelectrochemical modulation of biological cells and tissues. We show that by carrying out first-principles molecular dynamics simulations of the Si(100)/water interface in the presence of an electric field we can realistically correlate the computed flat-band potential and tunneling current images at the interface with experimentally measured capacitive and Faradaic currents. Specifically, we validate our simulations in the presence of bias by performing pulsed chronoamperometry measurements on Si wafers in solution. Consistent with prior experiments, our measurements and simulations indicate the presence of voltage-dependent capacitive currents at the interface. We also find that Faradaic currents are weakly dependent on the applied bias, which we relate to surface defects present in newly prepared samples.
- Award ID(s):
- Publication Date:
- NSF-PAR ID:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Page Range or eLocation-ID:
- Article No. e2114929118
- Proceedings of the National Academy of Sciences
- Sponsoring Org:
- National Science Foundation
More Like this
Unbiased solar H 2 production with current density up to 23 mA cm −2 by Swiss-cheese black Si coupled with wastewater bioanodeUnbiased photoelectrochemical hydrogen production with high efficiency and durability is highly desired for solar energy storage. Here, we report a microbial photoelectrochemical (MPEC) system that demonstrated superior performance when equipped with bioanodes and black silicon photocathode with a unique “Swiss-cheese” interface. The MPEC utilizes the chemical energy embedded in wastewater organics to boost solar H 2 production, which overcomes barriers on anode H 2 O oxidation. Without any bias, the MPEC generates a record photocurrent (up to 23 mA cm −2 ) and retains prolonged stability for over 90 hours with high Faradaic efficiency (96–99%). The calculated turnover number for MoS x catalyst during a 90 h period is 495 471 with an average frequency of 1.53 s −1 . The system replaced pure water on the anode with actual wastewater and achieved waste organic removal up to 16 kg COD m −2 photocathode per day. Cost credits from concurrent wastewater treatment and low-cost design make photoelectrochemical H 2 production practical for the first time.
Unbiased solar H2 production with current density up to 23 mA cm2 by Swiss-cheese black Si coupled with wastewater bioanodeUnbiased photoelectrochemical hydrogen production with high efficiency and durability is highly desired for solar energy storage. Here, we report a microbial photoelectrochemical (MPEC) system that demonstrated superior performance when equipped with bioanodes and black silicon photocathode with a unique ‘‘Swiss-cheese’’ interface. The MPEC utilizes the chemical energy embedded in wastewater organics to boost solar H2 production, which overcomes barriers on anode H2O oxidation. Without any bias, the MPEC generates a record photocurrent (up to 23 mA cm2) and retains prolonged stability for over 90 hours with high Faradaic efficiency (96–99%). The calculated turnover number for MoSx catalyst during a 90 h period is 495 471 with an average frequency of 1.53 s1 . The system replaced pure water on the anode with actual wastewater and achieved waste organic removal up to 16 kg COD m2 photocathode per day. Cost credits from concurrent wastewater treatment and low-cost design make photoelectrochemical H2 production practical for the first time
CdSe is potentially an important material for making tandem junction solar cells with Si and CIGS. Thermodynamic calculations reveal the potential Shockley-Queisser efficiency of such a tandem cell to be in the 45% range. CdSe has the optimum bandgap (1.72eV) for a tandem cell with Si. In this paper, we show that this material system is indeed capable of achieving good electronic properties and reasonable devices can be made in the material. We report on fabricating CdSe materials and heterojunction CdSe solar cells in both superstrate and substrate configurations on FTO/glass and metal substrates. CdSe layer was deposited using thermal evaporation and then was post-treated with CdCl2 to enhance the grainsize and passivate grain boundaries. The device was an ideal heterojunction structure consisting of glass/FTO/n+CdS/ n-CdSe/p organic layer/NiO/ITO. The n+ CdS layer acted to prevent hole recombination at the n+/n interface, and the p organic layer (such as PEDOT:PSS or P3HT) acted to prevent electron recombination at the p+/n interface. The NiO layer was deposited on top of the organic layer to prevent decomposition of the organic layer during ITO deposition. World-record open-circuit voltages exceeding 800 mV and currents of ~15 mA/cm2 were obtained in devices. Detailed material measurements suchmore »
Capacitive deionization (CDI) technologies have gained intense attention for water purification and desalination in recent years. Inexpensive and widely available porous carbon materials have enabled the fast growth of electrosorption research, highlighting the promise of CDI as a potentially cost-effective technology to remove ions. Whereas the main focus of CDI has been on bulk desalination, there has been a recent shift towards electrosorption for selective ion separations. Heavy metals are pollutants that can have severe health impacts and are present in both industrial wastewater and groundwater leachates. Heavy metal ions, such as chromium, cadmium, or arsenic, are of great concern to traditional treatment technologies, due to their low concentration and the presence of competing species. The modification/functionalization of porous carbon and recent developments of faradaic and redox-active materials have offered a new avenue for selective ion-binding of heavy metal contaminants. Here, we review the progress in electrosorptive technologies for heavy metal separations. We provide an overview of the wide applicability of carbon-based electrodes for heavy metal removal. In parallel, we highlight the trend toward modification of carbon materials, new developments in faradaic interfaces, and the underlying physico-chemical mechanisms that promote selective heavy metal separations.
Insights into the behavior of nonanoic acid and its conjugate base at the air/water interface through a combined experimental and theoretical approachThe partitioning of medium-chain fatty acid surfactants such as nonanoic acid (NA) between the bulk phase and the air/water interface is of interest to a number of fields including marine and atmospheric chemistry. However, questions remain about the behavior of these molecules, the contributions of various relevant chemical equilibria, and the impact of pH, salt and bulk surfactant concentrations. In this study, the surface adsorption of nonanoic acid and its conjugate base is quantitatively investigated at various pH values, surfactant concentrations and the presence of salts. Surface concentrations of protonated and deprotonated species are dictated by surface-bulk equilibria which can be calculated from thermodynamic considerations. Notably we conclude that the surface dissociation constant of soluble surfactants cannot be directly obtained from these experimental measurements, however, we show that molecular dynamics (MD) simulation methods, such as free energy perturbation (FEP), can be used to calculate the surface acid dissociation constant relative to that in the bulk. These simulations show that nonanoic acid is less acidic at the surface compared to in the bulk solution with a p K a shift of 1.1 ± 0.6, yielding a predicted surface p K a of 5.9 ± 0.6. A thermodynamic cycle for nonanoic acidmore »