• Energy Research

The search for affordable high performance electrode materials in photoelectrochemical hydrogen production by solar water splitting is an ongoing quest. Hematite is a photoanode material with an electronic band gap suitable for efficient absorption of visible light in a photoelectrochemical cell (PEC). Although its poor electronic structure makes hematite a controversial candidate for PEC, it remains promising because it is an earth abundant, chemically stable and low cost material – necessary prerequisites for PEC to become a competitive cost-efficient solar fuel economy. In addition to reviewing some recent PEC research on hematite and its relevant physical and chemical characteristics, we show how hematite obtained by a low cost synthesis can be refined by hydrothermal treatment and further functionalized by coating with phycocyanin, a light harvesting protein known for photosynthesis in blue-green algae.

Abstract We have employed anomalous small angle X-ray scattering (ASAXS) and X-ray absorption in situ on an operating lithium ion battery cell with LiMn 2 O 4 as the positive electrode material. Manganese K-edge absorption spectra and scattering patterns were recorded at various stages of charge between 3.8 and 4.5 V. The shift of the manganese absorption K-edge was observed as a function of the charge of the electrode. Clear changes in the microstructure of the spinel at the 4 V plateau was observed even during the first charging cycle.

A facile and low-cost dip-coating process for the deposition of silicon doped hematite films (Si:α-Fe2O3) for hydrogen production by solar water splitting in photo-electrochemical cells (PEC) is presented. The precursors include iron nitrate, oleic acid, tetraethyl orthosilicate (TEOS) and tetrahydrofuran as dispersion agent. Sequential dip coating on transparent conducting oxides glass substrates with heat treatment steps at 500 °C and 760 °C yields mesoporous Si:α-Fe2O3 with a roughness factor of 17 and photocurrent densities >1 mA/cm2 at 1.23 V vs. reversible hydrogen electrode with SiOx underlayer and surface modification. A PEC demonstrator with 80 cm2 active area in 1 M potassium hydroxide yields a photocurrent of 35 mA at 1.5 AM irradiation with the corresponding hydrogen evolution at a Pt wire counter electrode.

AbstractArtificial photosynthesis (AP) is inspired by photosynthesis in nature. In AP, solar hydrogen can be produced by water splitting in photoelectrochemical cells (PEC). The necessary photoelectrodes are inorganic semiconductors. Light‐harvesting proteins and biocatalysts can be coupled with these photoelectrodes and thus form bioelectronic interfaces. We expand this concept toward PEC devices with vital bio‐organic components and interfaces, and their integration into the built environment.

The sun is the primary energy source of our planet and potentially can supply all societies with more than just their basic energy needs. Demand of electric energy can be satisfied with photovoltaics, however the global demand for fuels is even higher. The direct way to produce the solar fuel hydrogen is by water splitting in photoelectrochemical (PEC) cells, an artificial mimic of photosynthesis. There is currently strong resurging interest for solar fuels produced by PEC cells, but some fundamental technological problems need to be solved to make PEC water splitting an economic, competitive alternative. One of the problems is to provide a low cost, high performing water oxidizing and oxygen evolving photoanode in an environmentally benign setting. Hematite, α-Fe2O3, satisfies many requirements for a good PEC photoanode, but its efficiency is insufficient in its pristine form. A promising strategy for enhancing photocurrent density takes advantage of photosynthetic proteins. In this paper we give an overview of how electrode surfaces in general and hematite photoanodes in particular can be functionalized with light harvesting proteins. Specifically, we demonstrate how low-cost biomaterials such as cyanobacterial phycocyanin and enzymatically produced melanin increase the overall performance of virtually no-cost metal oxide photoanodes in a PEC system. The implementation of biomaterials changes the overall nature of the photoanode assembly in a way that aggressive alkaline electrolytes such as concentrated KOH are not required anymore. Rather, a more environmentally benign and pH neutral electrolyte can be used.

Conference report containing a summary of the Swiss Stakeholder Workshop held at Empa, Dübendorf on 27 September 2019. The workshop had the aim of community build- ing and was attended by over 30 participants from Switzerland, France, and South Africa. The secondary purpose of the work- shop was the inclusion of the previously competing ENERGY-X flagship project into a future joint project from SUNRISE and ENERGY-X. The workshop program had 20 technical presenta- tions including posters, a panel discussion and an interactive session.

Abstract On the timescale of solid oxide fuel cell (SOFC) system lifetime requirements, the thermodynamically predicted low-level substitution of chromium on the B-site of (La,Sr)MnO3 could be a source of cathode degradation underlying more overt and well-known chromium poisoning mechanisms. To study this phenomenon in isolation, electronic conductivity (σ) and electrochemical oxygen reduction activity of the (La0.8Sr0.2)0.98CrxMn1−xO3 model series (x = 0, 0.02, 0.05 or 0.1) were measured in air between 850 and 650 °C. Depending on the extent of chromium substitution and the measurement temperature, electrochemical impedance spectroscopy (EIS) results could be deconvoluted into a maximum of three contributions reflecting possible limiting processes such as oxide ion transport and dissociative adsorption. Chromium substitution resulted in lowered σ (from 174 S cm− 1 (x = 0) to 89 S cm− 1 (x = 0.1) at 850 °C) and a steady rise in associated activation energy (Ea) (from 0.105 ± 0.001 eV (x = 0) to 0.139 ± 0.001 eV (x = 0.1)). From EIS analyses, ohmic and polarisation resistances increased, whilst Ea for the overall oxygen reduction reaction also increased from 1.39 ± 0.04 eV (x = 0) to 1.48–1.54 ± 0.04 eV upon chromium substitution.

A SEM picture of the microspheroids (tilted), scheme depicting the vesicle templated sol–gel process and squared normalized electric field intensity distribution inside the microspheroid calculated by finite-difference time-domain simulation.