We investigated a range of different mesoporous NiO electrodes prepared by different research groups and private firms in Europe to determine the parameters which influence good quality photoelectrochemical devices. This benchmarking study aims to solve some of the discrepancies in the literature regarding the performance of p-DSCs due to differences in the quality of the device fabrication. The information obtained will lay the foundation for future photocatalytic systems based on sensitized NiO so that new dyes and catalysts can be tested with a standardized material. The textural and electrochemical properties of the semiconducting material are key to the performance of photocathodes. We found that both commercial and non-commercial NiO gave promising solar cell and water-splitting devices. The NiO samples which had the two highest solar cell efficiency (0.145% and 0.089%) also gave the best overall theoretical H2 conversion.

Mesoporous nickel oxide has been used as electrode material for p-type dye-sensitized solar cells (DSCs) for many years but no high efficiency cells have yet been obtained. One of the main issues that lowers the efficiency is the poor fill factor, for which a clear reason is still missing. In this paper we present the first evidence for a relation between applied potential and the charge recombination rate of the NiO electrode. In particular, we find biphasic recombination kinetics: a fast (15 ns) pathway attributed to the reaction with the holes in the valence band and a slow (1 ms) pathway assigned to the holes in the trap states. The fast component is the most relevant at positive potentials, while the slow component becomes more important at negative potentials. This means that at the working condition of the cell, the fast recombination is the most important. This could explain the low fill factor of NiO-based DSCs.

Nickel oxide has been used as the mesoporous electrode material for p-type dye sensitized solar cell (DSSC) for many years, but no high efficiency cells have been obtained yet. The poor results are commonly attributed to the lack of conductivity of the NiO film. In this paper we studied the electrical conduction of NiO mesoporous film with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). We used unsensitized NiO on FTO as an electrode with no dye adsorbed on the surface. Tests made with a DSSC device-like cell (FTO-Pt-I–/I3 –-NiO-FTO) showed a surprisingly high Faradaic current (20 mA/cm–2 at 1 V), proving a good electrical conductivity of mesoporous NiO. We also used lithium as dopant to improve the electrical properties of the film. The Li-doping resulted in widening the inert (not conductive) window in the CV plot. The EIS analysis clarified that this behavior is due to a strong dependence of the valence band shape and position with respect to the Li-doping concentration. Our results show that DSSC performance does not need to be limited by the conductivity of mesoporous NiO, which encourages more effort in p-type DSSC research based on this material.

Mesoporous NiO is used as p-type material in photoelectrochemical energy conversion devices. The presence of two kinds of hole traps can affect device performance. Here, after band-gap excitation, the relaxation of the hole into two different traps was observed and characterized.

How cations affect the electric double layer and the rates and selectivity of electrocatalytic processes