Search for: All records

Semiconductor particle suspension reactors hold promise as a possible low-cost strategy for solar water-splitting, but they face several challenges that have inhibited their solar-to hydrogen (STH) efficiencies. A tandem microparticle with a buried junction addresses some of these challenges and offers a pathway to high STH efficiency. As a slurry, the tandem microparticles need to be suspended and well dispersed with maximum light absorption for a minimal photoactive particle concentration. Herein, proof-of-concept Ni/np+-Si/FTO/TiO2 tandem microwire structures capable of unassisted solar water-splitting were investigated as a slurry using uplifting N2 carrier gas bubbles. Transmittance, reflectance, and absorptance of the slurry were characterized as a function of wavelength, bubble flowrate, and tandem microwire concentration using an integrating sphere. Notably, a slurry absorptance of 70−85% was achieved with only 1% of the solution volume filled with a photoactive material. Photochemical activity of the slurry was characterized with in situ monitoring of the photodegradation of methylene blue, including the effects of particle concentration, bubble flowrate, spectral mismatch, intermixed light scattering particles, and a back reflector. 

Slurries of semiconductor particles individually capable of unassisted light‐driven water‐splitting are modeled to have a promising path to low‐cost solar hydrogen generation, but they have had poor efficiencies. Tandem microparticle systems are a clear direction to pursue to increase efficiency. However, light absorption must be carefully managed in a tandem to prevent current mismatch in the subcells, which presents a possible challenge for tandem microwire particles suspended in a liquid. In this work, a Ni‐catalyzed Si/TiO₂tandem microwire slurry is used as a stand‐in for an ideal bandgap combination to demonstrate proof‐of‐concept in situ alignment of unassisted water‐splitting microwires with an external magnetic field. The Ni hydrogen evolution catalyst is selectively photodeposited at the exposed Si microwire core to serve as the cathode site as well as a handle for magnetic orientation. The frequency distribution of the suspended microwire orientation angles is determined as a function of magnetic field strength under dispersion with and without uplifting microbubbles. After magnetizing the Ni bulb, tandem microwires can be highly aligned in water under a magnetic field despite active dispersion from bubbling or convection.

 

The molecular catalyst diacetyl-bis( N -4-methyl-3-thiosemi-carbazonato)nickel( ii ) (NiATSM) was integrated with Si for light-driven hydrogen evolution from water. Compared to an equivalent loading of Ni metal, the NiATSM/p-Si electrode performed better. Durability of the surface-bound catalyst under operation in acid was achieved without covalent attachment by using Nafion binding. 

Electrocatalysis and photoelectrochemistry are critical to technologies like fuel cells, electrolysis, and solar fuels. Material stability and interfacial phenomena are central to the performance and long‐term viability of these technologies. Researchers need tools to uncover the fundamental processes occurring at the electrode/electrolyte interface. Numerous analytical instruments are well‐developed for material characterization, but many are ex situ techniques often performed under vacuum and without applied bias. Such measurements miss dynamic phenomena in the electrolyte under operational conditions. However, innovative advancements have allowed modification of these techniques for in situ characterization in liquid environments at electrochemically relevant conditions. This review explains some of the main in situ electrochemical characterization techniques, briefly explaining the principle of operation and highlighting key work in applying the method to investigate material stability and interfacial properties for electrocatalysts and photoelectrodes. Covered methods include spectroscopy (in situ UV–vis, ambient pressure X‐ray photoelectron spectroscopy (APXPS), and in situ Raman), mass spectrometry (on‐line inductively coupled plasma mass spectrometry (ICP‐MS) and differential electrochemical mass spectrometry (DEMS)), and microscopy (in situ transmission electron microscopy (TEM), electrochemical atomic force microscopy (EC‐AFM), electrochemical scanning tunneling microscopy (EC‐STM), and scanning electrochemical microscopy (SECM)). Each technique's capabilities and advantages/disadvantages are discussed and summarized for comparison.

 

The conversion of waste CO₂to value‐added chemicals through electrochemical reduction is a promising technology for mitigating climate change while simultaneously providing economic opportunities. The use of non‐aqueous solvents like methanol allows for higher CO₂availability and novel products. In this work, the electrochemistry of CO₂reduction in acidic methanol catholyte at a Pb working electrode was investigated while using a separate aqueous anolyte to promote a sustainable water oxidation half‐reaction. The selectivity among methyl formate (a product unique to reduction of CO₂in methanol), formic acid, and formate was critically dependent on the catholyte pH, with higher pH conditions leading to formate and low pH favoring methyl formate. The potential dependence of the product distribution in acidic catholyte was also investigated, with a faradaic efficiency for methyl formate as high as 75 % measured at −2.0 V vs. Ag/AgCl.