Photoelectrochemical Tandem Cells for Solar Water Splitting

Abstract

In order to be economically competitive with simple “brute force” (i.e., PV + electrolyzer) strategies or the production of promising solar fuels, like H2, from fossil fuels, a practical photoelectrochemical device must optimize cost, longevity, and performance. A promising approach that meets these requirements is the combination of stable and inexpensive oxide semiconductor electrodes in a tandem photoelectrochemical device. In this article, we give an overview of the field including an examination of the potential solar-to-fuel conversion efficiency expected in a device with realistic losses. We next discuss recent advances with increasing the performance of promising semiconductor electrode materials and highlight how these advances have led to state-of-the-art solar-to-chemical efficiencies in the 2–3% range in real devices. Challenges for further optimization are further outlined.

Solar-Powered Plasmon-Enhanced Heterogeneous Catalysis

“…Solar-powered water splitting [1,[63][64][65][66]] is a central technology in the realization of a sustainable energy economy based on clean and renewable energy vectors such as H 2 . The overall reaction is endothermic and can be divided into two half reactions, namely, the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), as follows:…”

“…A general approach is to accomplish each halfreaction separately by using one semiconductor for the OER (photoanode) and the other one for the HER (photocathode). These two separate electrodes are then assembled in the so-called tandem cell configuration (Figure 3C) [64,73]. This approach is particularly advantageous since it offers the possibility to explore several combinations of semiconductor materials with complementary absorption and stability features.…”

“…More recently, α-Fe 2 O 3 and BiVO 4 have emerged as promising photoanode materials because of good stability, optimal bandgap absorption (α-Fe 2 O 3 can reach a maximum theoretical solar-tohydrogen efficiency of 17%), and low cost [76][77][78]. The major limitation of α-Fe 2 O 3 for efficient light harvesting is the very short hole diffusion length (few nm) as compared to the light penetration depth (hundreds of nm at 550 nm) [64,77,79]. In other words, α-Fe 2 O 3 needs to be a few hundred nanometers thick in order to absorb the entire incident light but, as a main drawback, the photogenerated electron-hole pairs would undergo massive bulk recombination within a few nanometers.…”

Sol–gel copper chromium delafossite thin films as stable oxide photocathodes for water splitting

“…7 This requires the development of stable photocathodes based on abundant materials. In this context, only a few binary oxides have been described to exhibit p-type behavior (mainly cobalt, nickel, and, particularly copper oxides).…”

Mixed‐Metal Tungsten Oxide Photoanode Materials Made by Pulsed‐Laser in Liquids Synthesis

“…The performance of photoelectrodes is not just governed by sunlight absorption, but band edge positions of the material in contact with the liquid electrolyte, material conductivity, carrier lifetimes, and charge recombination processes also matter; structure size critically affects the probability of a photogenerated carrier to reach the photoelectrode-electrolyte interface. [9,16] Since photocurrent generation of complex semiconductors depends on many factors, [46] simple correlations are rarely found, especially when comparing different materials as in this work. Table 1 for nomenclature.…”