Photoelectrochemical (PEC) energy conversion systems have been considered as a highly potential strategy for clean solar fuel production, simultaneously addressing the energy and environment challenges we are facing. Tremendous research efforts have been made to design and develop feasible unassisted PEC systems that can efficiently split water into hydrogen (H2) and oxygen with only the energy input of sunlight. A fundamental understanding of the concepts involved in PEC water splitting and energy conversion efficiency enhancement for solar fuel production is important for better system design. This review gives a concise overview of the unassisted PEC devices with some state-of-the-art progress toward efficient PEC devices for future sustainable solar energy utilization.
Photocatalytic water splitting to produce H<sub>2</sub> and O<sub>2</sub> with semiconductor photocatalysts provides an attractive solution to
global energy and environmental problems. The development of photocatalysts with high efficiency, availability, and
stability under wide solar spectrum is paramount for the practical application of this technology. Nitrogen doping and
preparation of materials with desirable crystal structure and morphology are two important strategies of fine-tuning the
properties of semiconductor photocatalysts. In the present work, by synchronizing the two strategies, photocatalysts with
typical structures were doped with nitrogen with the aim of realizing efficient water splitting under wide solar spectrum.
After nitrogen doping, the absorption of the as-obtained N-doped photocatalysts was extended from the UV to the visible
region. The doped photocatalysts exhibited not only increased visible light absorbance but enhanced photocatalytic
hydrogen or oxygen production under light irradiation, in comparison to that of undoped parent compound. DFT
calculations indicated that the top of the valence band is composed of N2p states mixed with pre-existing O2p states,
which moved the valence band maximum (VBM) upwards, as a result, decreasing the band gap of the parent oxide
photocatalysts tremendously. The unique structures of the pristine materials were found to facilitate the homogeneous of
nitrogen nitrogen in the whole materials by offering excellent pathways for nitrogen doping process. This work
highlighted the importance of crystal structures on the doping of nitrogen, paving a new way for developing novel
functional photocatalytic materials.
The use of polyethersulfone (PES), an excellent but highly hydrophobic thermoplastic, as a matrix material for ionexchange
membranes was investigated. To make PES ion-exchangeable, sulfonate groups were introduced to the
polymer chains by sulfonation reaction with chlorosulfonic acid. The degree of sulfonation of sPES was estimated to be
21%. Preliminary experiments investigated the effect of polyethylene glycol (PEG) and Pluronic F127 as fillers to
improve the hydrophilicity of the membranes. Moreover, a lab scale electrodialysis cell has been designed and set up to
evaluate the performance of these novel membranes compared to the benchmark of commercial membranes. The results
show promising properties of ion-exchange capacity, water uptake, conductivity and hydophilicity from blended
membranes, comparable to commercial membranes, though the performance of the prepared membranes did not exceed
the commercial one. Further characterization of the transport properties of ion-exchange membranes need to be
investigated to be able to understand the effects of the fillers on the performance of the membranes in ED application.