Surface recombination at semiconductor electrodes

Photoelectrochemical Lithium Extraction from Waste Batteries

The amount of global hybrid-electric and all electric vehicle has increased dramatically in just five years and reached an all-time high of over 10 million units in 2022. A good deal of waste lithium (Li)-containing batteries from dead vehicles are invaluable unconventional resources with high usage of Li. However, the recycle of Li by green approaches is extremely inefficient and rare from waste batteries, giving rise to severe environmental pollutions and huge squandering of resources. Thus, in this mini review, we briefly summarized a green and promising route-photoelectrochemical (PEC) technology for extracting the Li from the waste lithium-containing batteries. This review first focuses on the critical factors of PEC performance, including light harvesting, charge-carrier dynamics, and surface chemical reactions. Subsequently, the conventional and PEC technologies applying in the area of Li recovery processes are analyzed and discussed in depth, and the potential challenges and future perspective for rational and healthy development of PEC Li extraction are provided positively.

Combining Modulated Techniques for the Analysis of Photosensitive Devices

Small-perturbation techniques such as impedance spectroscopy (IS), intensity-modulated photocurrent spectroscopy (IMPS), and intensity-modulated photovoltage spectroscopy (IMVS) are useful tools to characterize and model photovoltaic and photoelectrochemical devices. While the analysis of the impedance spectra is generally carried out using an equivalent circuit, the intensity-modulated spectroscopies are often analyzed through the measured characteristic response times. This makes the correlation between the two methods of analysis generally unclear. In this work, by taking into consideration the absorptance and separation efficiency, a unified theoretical framework and a procedure to combine the spectral analysis of the three techniques are proposed. Such a joint analysis of IS, IMPS, and IMVS spectra greatly reduces the sample space of possible equivalent circuits to model the device and allows obtaining parameters with high reliability. This theoretical approach is applied in the characterization of a silicon photodiode to demonstrate the validity of this methodology, which shows great potential to improve the quality of analysis of spectra obtained from frequency domain small-perturbation methods.

Investigating the Consistency of Models for Water Splitting Systems by Light and Voltage Modulated Techniques

The optimization of solar energy conversion devices relies on their accurate and nondestructive characterization. The small voltage perturbation techniques of impedance spectroscopy (IS) have proven to be very powerful to identify the main charge storage modes and charge transfer processes that control device operation. Here we establish the general connection between IS and light modulated techniques such as intensity modulated photocurrent (IMPS) and photovoltage spectroscopies (IMVS) for a general system that converts light to energy. We subsequently show how these techniques are related to the steady-state photocurrent and photovoltage and the external quantum efficiency. Finally, we express the IMPS and IMVS transfer functions in terms of the capacitive and resistive features of a general equivalent circuit of IS for the case of a photoanode used for solar fuel production. We critically discuss how much knowledge can be extracted from the combined use of those three techniques.

Efficient direct solar-to-hydrogen conversion by in situ interface transformation of a tandem structure

Photosynthesis is nature's route to convert intermittent solar irradiation into storable energy, while its use for an industrial energy supply is impaired by low efficiency. Artificial photosynthesis provides a promising alternative for efficient robust carbon-neutral renewable energy generation. The approach of direct hydrogen generation by photoelectrochemical water splitting utilizes customized tandem absorber structures to mimic the Z-scheme of natural photosynthesis. Here a combined chemical surface transformation of a tandem structure and catalyst deposition at ambient temperature yields photocurrents approaching the theoretical limit of the absorber and results in a solar-to-hydrogen efficiency of 14%. The potentiostatically assisted photoelectrode efficiency is 17%. Present benchmarks for integrated systems are clearly exceeded. Details of the in situ interface transformation, the electronic improvement and chemical passivation are presented. The surface functionalization procedure is widely applicable and can be precisely controlled, allowing further developments of high-efficiency robust hydrogen generators.

Zn-doped p-type gallium phosphide nanowire photocathodes from a surfactant-free solution synthesis

Gallium phosphide (GaP) nanowire photocathodes synthesized using a surfactant-free solution-liquid-solid (SLS) method were investigated for their photoelectrochemical evolution of hydrogen. Zinc as a p-type dopant was introduced into the nanowires during synthesis to optimize the photocathode's response. Investigation of the electrical properties of Zn-doped GaP nanowires confirmed their p-type conductivity. After optimization of the nanowire diameter and Zn doping concentration, higher absorbed photon-to-current efficiency (APCE) over the spectrum was achieved. The versatility of the SLS synthesis and the capability to control the electrical properties suggest that our approach could be generalized to other III-V and II-VI semiconductors.