Electrochemical and Photoelectrochemical Properties of Nickel Oxide (NiO) With Nanostructured Morphology for Photoconversion Applications

Abstract

The cost-effective production of chemicals in electrolytic cells and the conversion of the radiation energy into electrical energy in photoelectrochemical cells (PECs) require the use of electrodes with large surface area, which possess either electrocatalytic or photoelectrocatalytic properties. In this context nanostructured semiconductors are electrodic materials of great relevance because of the possibility of varying their photoelectrocatalytic properties in a controlled fashion via doping, dye-sensitization or modification of the conditions of deposition. Among semiconductors for electrolysers and PECs the class of the transition metal oxides (TMOs) with a particular focus on NiO interests for the chemical-physical inertness in ambient conditions and the intrinsic electroactivity in the solid state. The latter aspect implies the existence of capacitive properties in TMO and NiO electrodes which thus act as charge storage systems. After a comparative analysis of the (photo)electrochemical properties of nanostructured TMO electrodes in the configuration of thin film the use of NiO and analogs for the specific applications of water photoelectrolysis and, secondly, photoelectrochemical conversion of carbon dioxide will be discussed.

Electrochemically Deposited NiO Films as a Blocking Layer in p-Type Dye-Sensitized Solar Cells with an Impressive 45% Fill Factor

“…As a clear result of this, a higher number of injected holes could effectively reach the ITO-coated glass, resulting in a higher current density. Under these circumstances, dye-loading and current density values do not end up directly Apart from the V OC , the effect of the blocking layer is also evident on the FF that, in case of BL 1.10 V reached an impressive value of 45% that, as far as we are aware, is one of the higher ever reported [10]. As already stated before, the implementation of a blocking layer beneath the photocathode leads to a reduction in the recombination phenomena.…”

“…The device embedding a blocking layer made by Sol-Gel uses a V OC of 147.4 mV. Apart from the VOC, the effect of the blocking layer is also evident on the FF that, in case of BL 1.10 V reached an impressive value of 45% that, as far as we are aware, is one of the higher ever reported [10]. As already stated before, the implementation of a blocking layer beneath the photocathode leads to a reduction in the recombination phenomena.…”

“…Interestingly, both these drawbacks could be overcome at once through the implementation of a photoactive counter-electrode, based on a sensitized p-type semiconductor [8,9]. The most widely employed semiconductor in p-type DSSCs is nickel oxide (NiO) [10], although some attempts have been also made with CuO [11], Cu2O [12,13] and other composite materials [14][15][16][17]. It is worth mentioning that n-type (i.e., TiO2-based) devices have been thoroughly investigated since their first appearance in 1991 [18], while Grätzel and collaborators reached a remarkable 13% of photo conversion efficiency (PCE) in 2014 [19].…”

Hierarchical NiO/CMK-3 Photocathode for a p-Type Dye-Sensitized Solar Cell with Improved Photoelectrochemical Performance and Fast Hole Transfer

“…Conventional low-cost dye-sensitized solar cells based on n-type nanocrystalline TiO 2 photoanodes (n-DSSCs) have attracted great interest for several years. The photocurrent is generated in these devices from dye-sensitized electron injection into n-type semiconductors, and conversion efficiency values as high as 12.3% have been reported [1]. Recently, dye-sensitized solar cells based on p-type semiconductors (p-DSSCs) have also attracted growing attention [2][3][4][5].…”

“…They are caused by (i) the fast charge recombination between the redox mediator dye and holes generated in the NiO and (ii) the overall low light-harvesting efficiency [7,8]. It is believed that the nature and morphology of nanocrystalline NiO has a great influence on the hole transfer processes that occur in the semiconductor electrode [9][10][11][12][13][14]. Although NiO nanoparticles were viewed as a promising material for p-DSSCs, they cannot fulfill all of the requirements for the target application.…”