A study of Ni + 8YSZ/8YSZ/La0.6Sr0.4CoO3−δ ITSOFC fabricated by atmospheric plasma spraying

An intermediate temperature solid oxide fuel cell (ITSOFC) based on 8YSZ electrolyte, La_0.6Sr_0.4CoO_3−δ (LSCo) cathode, and Ni − 8YSZ anode coatings were consecutively deposited onto a porous Ni-plate substrate by atmospheric plasma spraying (APS). The spray parameters including current, argon and hydrogen flow rate, and powder feed rate were investigated by an orthogonal experiment to fabricate a thin gas-tight 8YSZ electrolyte coating (80 μm). By proper selection of the spray parameters to decrease the particles velocity and temperature, the sprayed NiO + 8YSZ coating after reducing with hydrogen shows a good electrocatalytic activity for H₂ oxidation. With the same treatment, 100–170 μm dimensions LSCo particle could keep phase structure after spraying. And the deposited LSCo cathode shows a good cathode performance and chemical compatibility with 8YSZ electrolyte after operating at 800 °C for 50 h. Output power density of the sprayed cell achieved 410 mW cm⁻² at 850 °C and 260 mW cm⁻² at 800 °C. Electrochemical characterization indicated that IR drop of 8YSZ electrolyte, cathodic polarization, and the contact resistance at LSCo/8YSZ interface were the main factors restricting the cell performance. The results suggested that the use of APS cell allowed the reduction of the operating temperature of the SOFC to below 850 °C with lower production costs.     

Fabrication and characterization of a YSZ/YDC composite electrolyte by a sol–gel coating method

The compatibility of a composite electrolyte composed of a yttria stabilized zirconia (YSZ) film and a yttria-doped ceria (YDC) substrate in a solid oxide fuel cell (SOFC) that can be operated under 800 °C was evaluated. The YSZ film coated on a YDC substrate was derived from a polymeric YSZ sol using a sol–gel spin coating method followed by heat-treatment at 1400 °C for 2 h. The SEM and XRD analysis indicated that there were no cracks, pinholes, or byproducts. The composite electrolyte comprising a YSZ film of 2 μm thickness and a YDC substrate of 1.6 mm thickness was used in a single cell performance test. A 0.5 V higher value of open circuit voltage (OCV) was found for the composite electrolyte single cell compared with an uncoated YDC single cell between 700 and 1050 °C and confirmed that the YSZ film was an electron blocking layer. The maximum power density of the composite electrolyte single cell at 800 °C, 122 mW/cm² at 285 mA/cm², is comparable with that of a YSZ single cell with the same thickness at 1000 °C, namely 144 mW/cm² at 330 mA/cm². The hypothetical oxygen partial pressure at the interface between the YSZ film and the YDC substrate for the composite electrolyte with the same thickness ratio at 800 °C is 5.58×10⁻¹⁸ atm which is two orders of magnitude higher than the equilibrium oxygen partial pressure of Ce₂O₃/CeO₂, 2.5×10⁻²⁰ atm, at the same temperature.     

Fabrication and characterization of anode-supported single chamber solid oxide fuel cell based on La0.6Sr0.4Co0.2Fe0.8O3−δ–Ce0.9Gd0.1O1.95 composite cathode

Anode-supported solid oxide fuel cells consisting of nickel–gadolinium doped ceria (NiO–CGO, 60:40 wt%) anode, gadolinium doped ceria (CGO) electrolyte and lanthanum strontium cobaltite ferrite–gadolinium doped ceria (LSCF–CGO) cathode are developed and operated under single-chamber conditions, utilizing methane/air mixture. The cell performance is optimized regarding the electrolyte microstructure, cathode composition and testing conditions. The performance of the cell improves with the decrease of the thickness of the electrolyte and the increase of the ratio of methane to oxygen. The test cell with LSCF–CGO cathode (70:30 wt%) that was sintered at 1100 °C for 2 h and 150 μm dense electrolyte exhibits the maximum power output of ∼260 mW cm⁻² at 600 °C in CH₄/O₂ = 2 atmosphere.     

Anode-supported solid oxide fuel cell with yttria-stabilized zirconia/gadolinia-doped ceria bilalyer electrolyte prepared by wet ceramic co-sintering process

To protect the ceria electrolyte from reduction at the anode side, a thin film of yttria-stabilized zirconia (YSZ) is introduced as an electronic blocking layer to anode-supported gadolinia-doped ceria (GDC) electrolyte solid oxide fuel cells (SOFCs). Thin films of YSZ/GDC bilayer electrolyte are deposited onto anode substrates using a simple and cost-effective wet ceramic co-sintering process. A single cell, consisting of a YSZ (∼3 μm)/GDC (∼7 μm) bilayer electrolyte, a La_0.8Sr_0.2Co_0.2Fe_0.8O₃–GDC composite cathode and a Ni–YSZ cermet anode is tested in humidified hydrogen and air. The cell exhibited an open-circuit voltage (OCV) of 1.05 V at 800 °C, compared with 0.59 V for a single cell with a 10-μm GDC film but without a YSZ film. This indicates that the electronic conduction through the GDC electrolyte is successfully blocked by the deposited YSZ film. In spite of the desirable OCVs, the present YSZ/GDC bilayer electrolyte cell achieved a relatively low peak power density of 678 mW cm⁻² at 800 °C. This is attributed to severe mass transport limitations in the thick and low-porosity anode substrate at high current densities.     

GdBaCo2O5+x layered perovskite as an intermediate temperature solid oxide fuel cell cathode

GdBaCo₂O_5+x (GBCO) was evaluated as a cathode for intermediate-temperature solid oxide fuel cells. A porous layer of GBCO was deposited on an anode-supported fuel cell consisting of a 15 μm thick electrolyte of yttria-stabilized zirconia (YSZ) prepared by dense screen-printing and a Ni–YSZ cermet as an anode (Ni–YSZ/YSZ/GBCO). Values of power density of 150 mW cm⁻² at 700 °C and ca. 250 mW cm⁻² at 800 °C are reported for this standard configuration using 5% of H₂ in nitrogen as fuel. An intermediate porous layer of YSZ was introduced between the electrolyte and the cathode improving the performance of the cell. Values for power density of 300 mW cm⁻² at 700 °C and ca. 500 mW cm⁻² at 800 °C in this configuration were achieved.     

Multilayer tape casting of large-scale anode-supported thin-film electrolyte solid oxide fuel cells

Tape casting is conventionally used to prepare individual, relatively thick components (i.e., the anode or electrolyte supporting layer) for solid oxide fuel cells (SOFCs). In this research, a multilayer ceramic structure is prepared by sequentially tape casting ceramic slurries of different compositions onto a Mylar carrier followed by co-sintering at 1400 °C. The resulting half-cells contains a 300 μm thick NiO–yttria-stabilized zirconia (YSZ) anode support, a 20 μm NiO–YSZ anode functional layer, and an 8 μm YSZ electrolyte membrane. Complete SOFCs are obtained after applying a Gd_0.1Ce_0.9O₂ (GDC) barrier layer and a Sm_0.5Sr_0.5CoO₃ (SSC) -GDC cathode by using a wet-slurry spray method. The 50 mm × 50 mm SOFCs produce peak power densities of 337, 554, 772, and 923 mW/cm² at 600, 650, 700, and 750 °C, respectively, on hydrogen fuel. A short stack including four 100 mm × 150 mm cells is assembled and tested. Each stack repeat unit (one cell and one interconnect) generates around 28.5 W of electrical power at a 300 mA/cm² current density and 700 °C.     

Diagnostic examination of thermally abused high-power lithium-ion cells

The inherent thermal instability of lithium-ion cells is a significant impediment to their widespread commercialization for hybrid-electric vehicle applications. Cells containing conventional organic electrolyte-based chemistries are prone to thermal runaway at temperatures around 180 °C. We conducted accelerating rate calorimetry measurements on high-power 18650-type lithium-ion cells in an effort to decipher the sequence of events leading to thermal runaway. In addition, electrode and separator samples harvested from a cell that was heated to 150 °C then air-quenched to room temperature were examined by microscopy, spectroscopy, and diffraction techniques. Self-heating of the cell began at 84 °C. The gases generated in the cell included CO₂ and CO, and smaller quantities of H₂, C₂H₄, CH₄, and C₂H₆. The main changes on cell heating to 150 °C were observed on the anode surface, which was covered by a thick layer of surface deposits that included LiF and inorganic and organo-phosphate compounds. The sources of gas generation and the mechanisms leading to the formation of compounds observed on the electrode surfaces are discussed.     

Effects of TiO2 and SDC addition on the properties of YSZ electrolyte

In this study, we investigate the effects of adding titanium dioxide (TiO₂) and samarium doped cerium oxide (SDC) on the properties of yttrium-stabilized zirconia (YSZ) electrolyte. The microstructure, mechanical, and electrochemical properties of the electrolyte are investigated. The performance in CO₂ electrolysis is measured by supplying carbon dioxide to Ni-YSZ electrode and nitrogen to LSM electrode. Results show that TiO₂ and SDC addition can reduce the sintering temperature and increase grain size. The ionic conductivity is 0.123 S cm⁻¹ at 1000 °C. In addition, the thermal expansion coefficient at 1000 °C is 8.25 × 10⁻⁶ K⁻¹. The current density of the cell is 439 mA cm⁻² at 1.3 V and 1000 °C in solid oxide electrolysis cell.     

Electrochemical characterization of Pr2CuO4 cathode for IT-SOFC

The electrochemical properties of Pr₂CuO₄ (PCO) electrode screen-printed on Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte were investigated. PCO was synthesized by a solid-state route from the stoichiometric mixture of oxides at 1273 K, 20 h. Thermogravimetric analysis (TGA) of PCO both in air and Ar demonstrated its stability up to 1173 K. X-ray powder diffraction study of the PCO–CGO mixture annealed in air at 1173 K for 100 h did not reveal chemical interaction between materials. The oxygen reduction on porous PCO electrodes applied on CGO electrolyte was studied in a symmetrical cell configuration by AC impedance spectroscopy at OCV conditions at 773–1173 K and pO₂$p_{{\text{O}}_2}$ = 10⁻⁴–1 atm. Analysis of the data revealed that depending on temperature and oxygen partial pressure different rate-determining steps of the overall oxygen reduction reaction take place. Calculated value of area specific resistance (ASR) of PCO electrode is 1.7 ± 0.2 Ω cm² at 973 K in air and it is constant after 6 subsequent thermocycles. We have found that oxygen reduction on PCO applied on CGO takes mainly place at the triple-phase boundary (TPB) since Adler–Lane–Steele (ALS) model is not valid. Therefore electrochemical characteristics of PCO electrode can be improved by further optimization of both microstructure of the electrode and electrode/electrolyte interface and PCO can be considered as a promising cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC).     

Pr1.8La0.2Ni0.74Cu0.21Ga0.05O4+δ as a potential cathode material with CO2 resistance for intermediate temperature solid oxide fuel cell

Pr_1.8La_0.2Ni_0.74Cu_0.21Ga_0.05O_4+δ (PLNCG), a mixed ionic electron conductor (MIEC) with a K₂NiF₄-type structure, has been studied as a potential cathode material based on YSZ (ZrO₂ with 8 mol% Y₂O₃) electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). The X-ray diffraction (XRD) analysis reveals that the good chemical compatibility between the PLNCG and YSZ. The maximum electric conductivity of the PLNCG appeared at about 460 °C and the value was 32 S cm⁻¹ in air and 34 S cm⁻¹ in O₂, respectively. A hollow fiber SOFC was fabricated with the PLNCG as the cathode, NiO–YSZ (1:1; w/w) as the anode and YSZ as the electrolyte. The maximum power density of the cell is 876 mW cm⁻² and the corresponding polarization resistance of the cell is 0.41 Ω cm² at 750 °C. Furthermore, the PLNCG cathode shows an excellent CO₂ resistance in the operation temperature range. The maximum power density of the cell is similar to that when the cathode is exposed to air. Furthermore, the cell performance is stable when the CO₂ concentrations in the air vary from 0 to 10 vol.% at both 700 and 750 °C. These results indicate that the PLNCG can be a good candidate for CO₂ resistance cathode materials of IT-SOFCs based on YSZ electrolyte.     

Effect of Li2CO3 additive on gas generation in lithium-ion batteries

To elucidate the mechanism of gas generation during charge–discharge cycling of a lithium-ion cell, the generated gases and passive films on the carbon electrode are examined by means of gas chromatography (GC) and Fourier transform infrared (FTIR) spectroscopy. In ethyl carbonate/dimethyl carbonate and ethyl carbonate/diethyl carbonate 1 M LiPF₆ electrolytes, the detected gaseous products are CO₂, CO, CH₄, C₂H₄, C₂H₆, etc. The FTIR spectrum of the surface of the carbon electrode shows bands which correspond to Li₂CO₃, ROCO₂Li, (ROCO₂Li)₂, and RCO₂Li. These results suggest that gas evolution is caused by electrode decomposition, reactive trace impurities, and electrolyte reduction. The surface of the electrode is composed of electrolyte reduction products. When 0.05 M Li₂CO₃ is added as an electrolyte additive, the total volume of generated gases is reduced, and the discharge capacity and the conductivity of lithium-ions are increased. These results can be explained by a more compact and thin ‘solid electrolyte interface’ film on the carbon electrode formed by Li₂CO₃, which effectively prevents solvent co-intercalation and carbon exfoliation.     

Effects of coal syngas major compositions on Ni/YSZ anode-supported solid oxide fuel cells

This paper presents a systematical evaluation of the effects of CO₂, H₂O, CO, N₂ and CH₄ in the coal syngas on the properties of typical Ni/YSZ anode-supported solid oxide fuel cells (SOFCs). The results show that CO₂, H₂O, CO, N₂ and CH₄ have complicated effects on the cell performance and the electrochemical impedance spectra (EIS) analysis reveals the addition of these gases influences electrode processes such as the oxygen ion exchange from YSZ to anode TPBs, the charge transfer at the anode TPBs, gas diffusion and conversion at the anode. Two kinds of mixture gases with different compositions are thus constituted and used as fuel for aging test on two cells at 750 °C. No degradation or carbon deposition is observed for the cell fueled with 40% H₂-20% CO-20% H₂O-20% CO₂ for 360 h while the cell fueled with 50% H₂-30% CO-10% H₂O-10% CO₂ exhibits an abrupt degradation after 50 h due to the severe carbon deposition.     

Electrical,thermal, and H2O and CO2 poisoning behaviors of PrNi0.5Co0.5O3-δ electrode for intermediate temperature protonic ceramic electrochemical cells

PrNi_0.5Co_0.5O_3-δ (PNC) exhibits adequate total electrical conductivity (～300 S/cm at 400–600 °C) and moisture has no significant effect on it. The thermal expansion coefficient of PNC is 17.6 × 10^?6/K by dilatometry and 18.43 × 10^?6/K by in situ XRD. PNC also demonstrates chemical stability against H₂O and CO₂. However, PNC symmetrical cell over proton-conducting BaZr_0.4Ce_0.4Y_0.1Yb_0.1O_3-δ (BZCYYb4411) electrolyte shows significant H₂O and CO₂ poisoning when those are introduced into O₂–N₂ mixture. In comparison, symmetrical cells with PNC electrode over the oxygen ion conducting Ce_0.9Gd_0.1O_2-δ (GDC) electrolyte show no H₂O and CO₂ poisoning under similar conditions. It is hypothesized that poisoning from H₂O and CO₂ of the PNC proton conducting symmetrical cell is caused by their adsorption on the BZCYYb4411 electrolyte instead of PNC electrode. Such a hypothesis is supported by the H₂O and CO₂ adsorption behaviors on PNC and BZCYYb4411 powder surfaces, as measured by temperature programmed desorption (TPD).     

Application of CuNi–CeO2 fuel electrode in oxygen electrode supported reversible solid oxide cell

The oxygen electrode-supported reversible solid oxide cell (RSOC) has demonstrated distinguishing advantages of fuel flexibility, shorter gas diffusion path and more choices for fuel electrode materials. However, there are serious drawbacks including the difficulty of co-firing the oxygen electrode and electrolyte, and the inefficient electrochemical performance. In this study, a (La_0.8Sr_0.2)_0.95MnO_3-δ (LSM) supported RSOC with the configuration of La_0.6Sr_0.4Fe_0.9Sc_0.1O_3-δ (LSFSc)-YSZ/YSZ/CuNi–CeO₂-YSZ is fabricated by tape casting, co-sintering and impregnation technologies. The single cell is evaluated at both fuel cell (FC) and electrolysis cell (EC) mode. Significant maximum power density of 436.0 and 377 mW cm^?2 is obtained at 750 °C in H₂ and CH₄ fuel atmospheres, respectively. At electrolysis voltage of 1.3 V and 50% steam content, current density of ?0.718, ?0.397, ?0.198 and ?0.081 A cm^?2 is obtained at 750, 700, 650 and 600 °C respectively. Much higher electrolysis performance than FC mode is exhibited probably due to the optimized electrodes with increased triple phase boundary (TPB) area and faster gas diffusion (oxygen and steam) and electrochemical reactions for water splitting. Additionally, the short-term stability of single cell in H₂ and CH₄ are also studied.     

Syngas production through CH4-assisted co-electrolysis of H2O and CO2 in La0.8Sr0.2Cr0.5Fe0.5O3-δ-Zr0.84Y0.16O2-δ electrode-supported solid oxide electrolysis cells

High temperature co-electrolysis of H₂O/CO₂ allows for clean production of syngas using renewable energy, and the novel fuel-assisted electrolysis can effectively reduce consumption of electricity. Here, we report on symmetric cells YSZ-LSCrF | YSZ | YSZ-LSCrF, impregnated with Ni-SDC catalysts, for CH₄-assisted co-electrolysis of H₂O/CO₂. The required voltages to achieve an electrolysis current density of ?400 mA·cm^?2 at 850 °C are 1.0 V for the conventional co-electrolysis and 0.3 V for the CH₄-assisted co-electrolysis, indicative of a 70% reduction in the electricity consumption. For an inlet of H₂O/CO₂ (50/50 vol), syngas with a H₂:CO ratio of ≈2 can be always produced from the cathode under different current densities. In contrast, the anode effluent strongly depends upon the electrolysis current density and the operating temperature, with syngas favorably produced under moderate current densities at higher temperatures. It is demonstrated that syngas with a H₂:CO ratio of ≈2 can be produced from the anode at a formation rate of 6.5·mL min^?1·cm^?2 when operated at 850 °C with an electrolysis current density of ?450 mA·cm^?2.     

Enhanced production of methane through the use of a catalytic Ni–Fe pre-layer in a solid oxide co-electrolyser

A composite cermet consisting in a Ni–Fe alloy and Ce_0.9Gd_0.1O_2-x (CGO) was prepared and used as an electrocatalytic pre-layer in a conventional solid oxide electrolyser (SOEC) for the co-electrolysis of H₂O and CO₂. The electrocatalyst showed two main phases ascribed to trevorite (NiFe₂O₄, 78 wt %) and metallic Ni (22 wt %) and an average crystallite size of 27 nm. The role of the Ni–Fe electrocatalyst in promoting CH₄ formation was analysed by comparing gas-chromatographic and electrochemical results obtained for coated and bare cells. A slight increase of series resistance was observed for the coated cell (0.85 vs 0.53 Ω cm²) at 525 °C. However, the coated cell demonstrated an enhanced CH₄ production in the entire temperature range investigated (525–800 °C). Contrarily to what observed for the bare cell which mainly produced syngas, the coated cell allowed to achieve a high yield of methane (between 67% at 525 °C and 35% at 800 °C) with selectivity to CH₄ between 94% at 525 °C and 51% at 800 °C. The selectivity to CO for the coated cell was relatively low (between 6% at 525 °C and 48% at 800 °C). Whereas, the bare cell showed 98–100% selectivity to CO along the entire temperature range). Durability studies showed the possible occurrence of delamination issues as consequence of carbon formation at the interface between the supporting cathode and the electrolyte as observed from the morphological analysis of SOEC cells after operation.     

Lower flammability limit of hydrogen/air mixture under different electrode parameters,initial pressure and diluent gas

The investigation of the lower flammability limit (LFL) is essential to the security application of hydrogen. In the present work, the LFL of hydrogen under a variety of conditions is systematically measured. The effect of electrode gap length (2–4 mm), electrode shape (30°, 90°, and spherical) and initial pressure (40–200 kPa) on the LFL of hydrogen/air mixture are analyzed. It shows that the LFL of hydrogen/air mixture increases with the increase of initial pressure and decreases with the increase of electrode gap length. The LFL of 30° electrodes is higher than that of 90° and spherical electrodes at the initial pressure higher than 80 kPa. Besides, the LFL of hydrogen/air mixture diluted with inert gas (CO₂ and N₂) at different initial pressure (50 kPa, 100 kPa, and 150 kPa) is investigated. The LFL of H₂/air/CO₂ mixture increases with increasing CO₂ concentration, while the LFL of H₂/air/N₂ mixture is almost unchanged under different N₂ concentration.     

Gadolinium doped ceria-impregnated nickel-yttria stabilised zirconia cathode for solid oxide electrolysis cell

Steam electrolysis (H₂O → H₂ + 0.5O₂) was investigated in solid oxide electrolysis cells (SOECs). The electrochemical performance of GDC-impregnated Ni-YSZ and 0.5% wt Rh-GDC-impregnated Ni-YSZ was compared to a composite Ni-YSZ and Ni-GDC electrode using a three-electrode set-up. The electrocatalytic activity in electrolysis mode of the Ni-YSZ electrode was enhanced by GDC impregnation. The Rh-GDC-impregnated Ni-YSZ exhibited significantly improved performance, and the electrode exhibited comparable performance between the SOEC and SOFC modes, close to the performance of the composite Ni-GDC electrode. The performance and durability of a single cell GDC-impregnated Ni-YSZ/YSZ/LSM-YSZ with an H₂ electrode support were investigated. The cell performance increased with increasing temperature (700 °C-800 °C) and exhibited comparable performance with variation of the steam-to-hydrogen ratio (50/50 to 90/10). The durability in the electrolysis mode of the Ni-YSZ/YSZ/LSM-YSZ cell was also significantly improved by the GDC impregnation (200 h, 0.1 A/cm², 800 °C, H₂O/H₂ = 70/30).     

Application of a micro-channel reactor for process intensification in high purity syngas production via H2O/CO2 co-splitting

A stainless steel micro-channel reactor was tailor-made to an in house-design for process intensification propose. The reactor was used for a two-step thermochemical cycles of H₂O and CO₂ co-splitting reaction, in the presence of La_0.3Sr_0.7Co_0.7Fe_0.3O₃ (LSCF). LSCF was coated inside the reactor using wash-coat technique. Oxygen storage capacity of LSCF was determined at 4465 μmol/g, using H₂-TPR technique. H₂O-TPSR and CO₂-TPSR results suggested that a formation of surface hydroxyl group was the cause of H₂O splitting favorable behavior of LSCF. Optimal operating reduction/oxidation temperature was found at 700 °C, giving 2266 μmol/g of H₂, 705 μmol/g of CO, and 67% of solid conversion, when the H₂O and CO₂ ratio was 1 to 1, and WSHV was 186,000 mL/g.h. Activation energy of H₂O spitting and CO₂ splitting was estimated at 87.33 kJ/mol, and 102.85 kJ/mol The pre-exponential factor of H2O splitting and CO2 splitting was 595.24 s^?1 and 698.79 s^?1, respectively.     

Co-free La0.6Sr0.4Fe0.9Nb0.1O3-δ symmetric electrode for hydrogen and carbon monoxide solid oxide fuel cell

Co-free La_0.6Sr_0.4FeO_3-δ (LSFNb₀) and La_0.6Sr_0.4Fe_0.9Nb_0.1O_3-δ (LSFNb_0.1) perovskite oxides were prepared by a standard solid-state reaction method. The structural stability and electrochemical performance of La_0.6Sr_0.4Fe_0.9Nb_0.1O_3-δ as both cathode and anode were studied. Nb dopant in LSFNb₀ significantly enhances the structural and chemical stability in anode condition. At 800 °C, the polarization resistances (Rp) of LSFNb_0.1 symmetric electrode based on YSZ electrolyte are 0.5 and 0.05 Ω cm² in H₂ and air, respectively. The peak power densities of LSFNb_0.1 based on LSGM electrolyte-supported SSOFCs are 934 and 707 mW cm⁻² at 850 °C in H₂ (3% H₂O) and dry CO, respectively. Moreover, the symmetric cell exhibits reasonable stability in both H₂ and CO fuel, suggesting that La_0.6Sr_0.4Fe_0.9Nb_0.1O_3-δ may be a potential symmetric electrode material for hydrogen and carbon monoxide SOFCs.