Dino Klotz

• Dr.-Ing.
• Professor (Assistant) at I2CNER - International Institute for Carbon Neutral Energy Research, Fukuoka, Kyushu, Japan

Solid oxide fuel cells have the potential to render the conversion from fuel to electrical energy more efficienct while lowering emissions. The technology, however, suffers from performance degradation due to...

Nanocellulose is a sustainable material which holds promise for many energy-related applications. Here, nanocrystalline cellulose is used to prepare proton exchange membranes (PEMs). Normally, this nanomaterial is highly dispersible in water, preventing its use as an ionomer in many electrochemical applications. To solve this, we utilized a sulfoni...

jats:p>While Cr poisoning of the oxygen reduction reaction (ORR) at SOFC cathodes is widely agreed to involve deactivation of oxygen exchange sites, the degradation mechanism remains ambiguous. Here, we selected an alternative cathode material Pr 0.1 Ce 0.9 O 2− δ , free of Sr segregation, to systematically investigate the effect of Cr-induced degr...

Grain boundary conductivity limitations are ubiquitous in material science. We show that illumination with above-bandgap light can decrease the grain boundary resistance in solid ionic conductors. Specifically, we demonstrate the increase of the grain boundary conductance of a 3 mol% Gd-doped ceria thin film by a factor of approximately 3.5 at 250...

Current greenhouse gas emissions suggest that keeping global temperature increase below 1.5 degrees, as espoused in the Paris Agreements will be challenging, and to do so, the achievement of carbon neutrality is of utmost importance. It is also clear that no single solution can meet the carbon neutral challenge, so it is essential for scientific re...

The electrochemical properties of photoelectrodes must be measured accurately and precisely to enable better comparisons between different materials. Along with the flat band potential, the interfacial charge transfer efficiency, which is the ratio between charge transfer rate at the photoelectrode surface and rate of charge carrier generation in t...

Impedance spectroscopy (IS) has great potential to become a standard technique for the characterization, analysis, and diagnosis of perovskite solar cells (PSC). However, the interpretation of IS data from PSC...

The oxygen evolution reaction (OER) at the surface of semiconductor photoanodes involves photo-generated holes that oxidize water. A certain fraction of the holes that reach the surface recombine with electrons from the conduction band, giving rise to the surface recombination loss. The charge transfer efficiency, xt, defined as the ratio between t...

Photoelectrochemical impedance spectroscopy (PEIS) is a useful tool for the characterization of photoelectrodes for solar water splitting. However, the analysis of PEIS spectra often involves a priori assumptions that might bias the results. This work puts forward an empirical method that analyzes the distribution of relaxation times (DRT), obtaine...

The spatial collection efficiency portrays the driving forces and loss mechanisms in photovoltaic and photoelectrochemical devices. It is defined as the fraction of photogenerated charge carriers created at a specific point within the device that contribute to the photocurrent. In stratified planar structures, the spatial collection efficiency can...

Transparent Fe1-xNixOOH overlayers (~2 nm thick) were deposited photoelectrochemically on (001) oriented heteroepitaxial Sn- and Zn-doped hematite (Fe2O3) thin film photoanodes. In both cases, the water photo-oxidation performance was improved by the co-catalyst overlayers. Intensity modulated photocurrent spectroscopy (IMPS) was applied to study t...

Electrochemical Impedance Spectroscopy (EIS) is a very powerful method for analyzing electrochemical systems with respect to the factors impacting conductivity, charge transfer and diffusion. A great advantage of EIS is that the system under test (SUT) can be measured in operando so that the SUT can be characterized under conditions as they prevail...

Oxide-based ionic and mixed ionic-electronic conductors (MIEC) play strategic roles in applications ranging from energy conversion and storage to thin film nano-ionic devices such as fuel cells, batteries, permeation membranes and nano-electronic memory and sensing devices. Most cost-effective production methods for fabricating both bulk and thin f...

Organic–inorganic lead halide perovskites have attracted great attention for use in solar cells, because of their efficient solar power conversion, along with compatibility with simple solution processing. To evaluate the operational stability of perovskite solar cells (PSCs), measurements on their current density–voltage (J−V) curves are periodica...

Organic‐inorganic halide perovskites are promising as the light absorber of solar cells because of their efficient solar power conversion. An issue frequently occurring in perovskite solar cells (PSCs) with a hole transport layer of N,N‐di(4‐methoxyphenyl)amino]‐9,9'‐spirobifluorene (spiro‐OMeTAD) is a quick performance degradation at high temperat...

Quasi-2D perovskites have attracted wide attention as the emitter of light-emitting diodes in recent years because of the ease of obtaining high external quantum efficiencies (EQEs). However, the quick degradation under continuous operation and significant EQE roll-off at high current densities are issues that need to be overcome for future practic...

Organic–inorganic halide perovskites are promising for use in solar cells because of their efficient solar power conversion. Current–voltage hysteresis and degradation under illumination are still issues that need to be solved for their future commercialization. However, why hysteresis and degradation occur in typical perovskite solar cell structur...

Oxide based Ionic and mixed Ionic – Electronic conductors play strategic roles in applications ranging from energy conversion and storage to thin-film nanoionic devices such as fuel cells, batteries, permeation membranes and nano-electronic memory and sensing devices. Most cost effective production methods for fabricating both bulk and thin films s...

Excess/unreacted lead iodide (PbI2 ) has been commonly used in perovskite films for the state-of-the-art solar cell applications. However, an understanding of intrinsic degradation mechanisms of perovskite solar cells (PSCs) containing unreacted PbI2 has been still insufficient and, therefore, needs to be clarified for better operational durability...

The current status of electrochemical impedance spectroscopy (EIS) and related analysis on perovskite solar cells (PSC) is still unsatisfactory. The provided models are still vague and not really helpful for guiding the efforts to develop more efficient and stable devices. Due to the slow and complex dynamics of these devices, the obtained spectra...

In article number 1801079, Chuanjiang Qin, Chihaya Adachi, and co‐workers adopt thermally stimulated current and electrochemical impedance spectroscopy measurements to reveal that carrier traps are generated in solar cells with CH3NH3PbI3 as a light absorber after operation at 85°C, which is higher than its phase transition temperature. Perovskite...

Impedance analysis is not an easy task. This becomes even more obvious if unusual shapes appear in the impedance diagram. Here, a low frequency hook with positive imaginary part is discussed that often leaves researchers clueless of how to handle it, especially if there is no common model for the device under test that includes the hook, which is a...

A power conversion efficiency of over 20% has been achieved in CH3NH3PbI3‐based perovskite solar cells (PSC), however, low thermal stability associated with the presence of a phase transition between tetragonal and cubic structures near room temperature is a major issue that must be overcome for future practical applications. Here, the influence of...

H2O2 is a sacrificial reductant that is often used as a hole scavenger to gain insight into photoanode properties. Here we show a distinct mechanism of H2O2 photo-oxidation on haematite (α-Fe2O3) photoanodes. We found that the photocurrent voltammograms display non-monotonous behaviour upon varying the H2O2 concentration, which is not in accord wit...

Photoelectrochemical impedance spectroscopy (PEIS) is a useful tool for the characterization of photoelectrodes for solar water splitting. However, the analysis of PEIS spectra often involves a priori assumptions that might bias the results. This work puts forward an empirical method that analyzes the distribution of relaxation times (DRT), obtaine...

Transparent Fe1-xNixOOH overlayers (~2 nm thick) were deposited photoelectrochemically on (001) oriented heteroepitaxial Sn- and Zn-doped hematite (α-Fe2O3) thin film photoanodes. In both cases, the water photo-oxidation performance was improved by the co-catalyst overlayers. Intensity modulated photocurrent spectroscopy (IMPS) was applied to study...

The spatial collection efficiency portrays the driving forces and loss mechanisms in photovoltaic and photoelectrochemical devices. It is defined as the fraction of photogenerated charge carriers created at a specific point within the device that contribute to the photocurrent. In stratified planar structures, the spatial collection efficiency can...

The oxygen evolution reaction (OER) at the surface of semiconductor photoanodes is critical for photoelectrochemical water splitting. This reaction involves photo-generated holes that oxidize water via charge transfer at the...

The performance of Ni/YSZ anodes has been shown to substantially benefit by a reverse current treatment of a solid oxide fuel cell. Within seconds, a solid state reaction builds a nanoscaled layer at the anode/electrolyte interface, thereby increasing the triple-phase boundary density considerably. The reaction mechanism is thoroughly studied using...

Doping with Ti enhances the electron conductivity in hematite (α-Fe2O3) photoanodes, as well as their photoelectrochemical properties with respect to undoped hematite photoanodes. However, the optimal doping level is unknown. This work examines the influence of the Ti doping level on the photoelectrochemical properties of thin (~50 nm) film hematit...

Electrochemical measurements on solid oxide fuel cells (SOFC) often uncover unusual readings. These are then ascribed to unknown material properties or newly discovered physical effects. However, a closer look shows that these are simply errors − mostly test artefacts. Our group has isolated many causes of error and developed reliable techniques to...

The orientation dependence on the photoelectrochemical properties of Sn-doped hematite photoanodes was studied by means of heteroepitaxial film growth. Nb-doped SnO2 (NTO) was first grown heteroepitaxially on c, a, r, and m plane single crystal sapphire substrates in three different orientations. Hematite was then grown in the (001), (110), and (10...

In this Perspective, we introduce intensity modulated photocurrent/voltage spectroscopy (IMPS and IMVS) as powerful tools for the analysis of charge carrier dynamics in photoelectrochemical (PEC) cells for solar water splitting, taking hematite (α-Fe2O3) photoanodes as a case study. We complete the picture by including photoelectrochemical impedanc...

In the present study, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)-Gd0.1Ce0.9O1.95 (GDC) composite cathodes with different volume fractions were fabricated by the screen printing method, and their polarization characteristics and microstructure parameters are evaluated. Cathode overpotentials were measured at the measurement condition of 700°C and 100% O2. Micros...

This article presents the combination of two established models: (i) a physically motivated zero-dimensional model that describes the static behavior of planar anode supported SOFCs with high precision in the whole range of technically relevant operating conditions and (ii) a performance model for large area SOFC which expands the behavior of a sma...

A parameter set obtained from a 1 cm2 size electrode cell is used to develop and calibrate a one-dimensional spatially resolved model. It is demonstrated that this performance model precalculates the evolving operating parameters along the gas channel of a large-sized cell. Input parameters are: (i) number of discretization elements N, accounting f...

The performance of nanoscaled Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) thin-film cathodes was investigated by electrochemical impedance spectroscopy (EIS). Thin-film cathodes derived by metal-organic deposition on Ce0.9Gd0.1O1.95 electrolyte pellets exhibited a film thickness of <100 nm. Performance evaluations of the nanoscaled BSCF thin-film cathodes were...

A method is presented of avoiding ambiguities in linear Kramers-Kronig validity tests due to under- and over-fitting. It is based on the observation that the parameters of the equivalent circuit model to be fitted start degenerating as soon as the model order chosen is too high and over-fitting is taking place. Hence, a measure of the degree of deg...

Lowering the operating temperature of solid oxide fuel cells (SOFC) to the range of 400 to 600°C requires powerful electrodes and thin-film electrolytes to compensate the increasing losses which arise from electrochemical processes at the electrodes and transport phenomena in the electrolyte. In this contribution we present for the first time the c...

Introduction Mixed ionic-electronic conductors as LSCF (La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3- δ ) and cermets like Ni/8YSZ (8 mol% Y 2 O 3 stabilized ZrO 2 ) are well-established cathode and anode materials for solid oxide fuel cells. At operating temperatures of 600 °C or below, electrode polarization losses as well as ohmic losses in the solid electr...

The performance of nanoscaled Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) thin-film cathodes was investigated by electrochemical impedance spectroscopy (EIS). Thin-film cathodes derived by metal-organic deposition on Ce0.9Gd0.1O1.95 electrolyte pellets exhibited a film thickness of <100 nm. Performance evaluations of the nanoscaled BSCF thin-film cathodes...

The design of state-of-the-art SOFC anodes limits the electrooxidation reaction inherently by its m-scaled microstructure. An increase in cell performance of anode-supported SOFCs (ASC) is achieved by a method, which induces the formation of an additional nanostructured Ni/YSZ layer in the electrochemically active region of the anode. This in-opera...

Ni particles are aligned by magnetic field during the drying process after screen-printing Ni/8YSZ (yttria-stabilized zirconia) paste. By applying a magnetic field, Ni particles are magnetically polarized, attracted to each other, and align along the magnetic field. It is proposed, that not only tortuosity of Ni but also that of YSZ and of pores is...

Anode supported SOFC single cells of different sizes - 1cm(2) and 16cm(2) - were measured and a 1D spatially resolved model was established accounting for the evolving operating parameters along the gas channel of the large cell. The model is calibrated with measurements on the 1cm(2) cell and reproduces the current/voltage characteristics of the 1...

A zero-dimensional and isothermal stationary model demonstrably predicting the current-voltage (C/V) characteristic of an anode supported SOFC single cell is for the first time verified for C/V characteristics measured in electrolysis mode. The accuracy of the presented model was increased by including the actual cell temperature under current load...

Electrochemical reaction kinetics at the electrodes of Solid Oxide Cells (SOCs) were investigated at 700 °C for two cells with different fuel electrode microstructures as well as on a third cell with a reduced active electrode area. Three fuel mixtures were investigated – hydrogen/steam and reformate fuels hydrogen/carbon-dioxide and hydrogen/metha...

In this work we present a method for the pre-identification of impedance measurements by the distribution of relaxation times (DRT). Several new features for parameter identification for electrochemical systems such as batteries and fuel cells are presented. The approach enables robust, accurate and consistent fit results for complex technically re...

A method is presented which obtains the half cell potentials of a sealed commercial cell from a measured OCV-curve. The underlying model is introduced and the physical interpretable parameters are discussed. The method is validated by two experiments simulating different aging mechanisms and future potentials are discussed.

Our zero-dimensional and isothermal stationary model predicts the current-voltage (C/V) characteristics of anode supported SOFC single cells in the direct as well as in the reverse (electrolyzer) operation mode. An extended model is presented for the electrolyzer mode, taking the corrected cell temperature as additional variable into consideration....

The electrooxidation reaction in the Ni/YSZ anode is still a limiting factor for the performance of anode supported SOFCs (ASC). An effective method for the improvement of anode performance is based on a short-time application of a high current density in reverse direction (reverse current treatment, RCT). In this contribution we evaluate this in-s...

Lithium iron phosphate is a promising candidate material for Li-Ion batteries. In this study, the rate determining processes are assessed in more detail in order to separate performance limiting factors. Electrochemical impedance spectroscopy (EIS) data of experimental LiFePO4/Lithium-cells are deconvoluted by the method of distribution of relaxati...

Electrothermal impedance spectroscopy (ETIS), is introduced as a new measurement method and thermal parameters derived from a pouch-type lithium-ion cell are presented. ETIS is a valuable tool for (i) the determination of the thermal impedance and (ii) the validation of thermal models. The excitation signal applied to the cell during measurement do...

A technique for fast impedance measurement in the time domain is presented. It is based on the Fourier transformation and includes various improvements compared to previous work in the literature. Namely, it minimizes the influence of spectral leakage and aliasing and reduces noise. This is proved by the theoretical error estimate for different mod...

The local morphology of the interface electrolyte/anode of solid oxide fuel cells has a strong effect on the electrochemically active triple-phase boundary length. Therefore, the electrical performance is expected to be enhanced by nanostructuring this interface. This study focuses on the anode functional layer (AFL) of Ni/8YSZ (Ni/8.5 mol % yttria...

Lithium iron phosphate is a promising cathode material for the use in hybrid electrical vehicles (HEV) meeting the demands of good stability during cycling and safe operation due to reduced risk of thermal runaway. However, slow solid state diffusion and poor electrical conductivity reduce power capability. For further improvement, the identificati...

Solid oxide fuel cells (SOFC) are of great interest for a diverse range of applications. Within the past 10 years, an increase in power density by one order of magnitude, a lowering of the operating temperature by 200 K, and degradation rates lower by a factor of 10, have been achieved on the cell and stack level. However, there is still room for f...

Lithium iron phosphate is a promising cathode material for the use in lithium-ion batteries meeting the demands of good stability during cycling and safe operation due to reduced risk of thermal runaway. However, slow solid state diffusion and poor electrical conductivity reduce power capability. For further improvement, all rate determining electr...

Lithium iron phosphate is a promising cathode material for the use in lithium-ion batteries meeting the demands of good stability during cycling and safe operation due to reduced risk of thermal runaway. However, slow solid state diffusion and poor electrical conductivity reduce power capability. For further improvement, the identification of the r...

The electrochemistry in the anode functional layer is still one of the performance limiting factors for the standard planar anode-supported SOFC (ASC). In this contribution we present an effective method for the improvement of anode performance. It is based on a short-time application of a high current density in reverse direction (reverse current...

Experimental EIS measurements on 1 cm² single cells were conducted over a wide range of operation conditions representing the variation of the local operating conditions in a stack. Parameter maps were established by identification of the loss processes using CNLS-fit for an equivalent circuit and validation by comparing the distribution of relaxat...

Many research studies have been focusing on the long-term stability of Ni/8YSZ cermet anodes. In this contribution we present an effective method for the recovery of anode supported cells (ASC) after degradation. The application of a short-time reverse current ended up with a significant drop in the area specific resistance (ASR) of the ASC. The re...

Impedance Spectroscopy for SOFC stacks and systems