H2 production from a single stage water–gas shift reaction over Pt/CeO2, Pt/ZrO2, and Pt/Ce(1−x)Zr(x)O2 catalysts

To develop a single stage water–gas shift reaction (WGS) catalyst for compact reformers, Pt/CeO₂, Pt/ZrO₂, and Pt/Ce_(1−x)Zr_(x)O₂ catalysts have been applied for the target reaction. The CeO₂/ZrO₂ ratio was systematically varied to optimize Pt/Ce_(1−x)Zr_(x)O₂ catalysts. Pt/CeO₂ showed the highest turnover frequency (TOF) and the lowest activation energy (E_a) among the catalysts tested in this study. It has been found that the reduction property of the catalyst is more important than the dispersion for a single stage WGS. Pt/CeO₂ catalyst also showed stable catalytic performance. Thus, Pt/CeO₂ can be a promising catalyst for a single stage WGS for compact reformers.     

Catalytic and DRIFTS study of the WGS reaction on Pt-based catalysts

The water–gas shift (WGS) activity of Pt/SiO₂, Pt/CeO₂ and Pt/TiO₂ catalysts was studied by in-situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). Samples contained a similar amount of Pt, between 0.34 and 0.50%, and were characterized by employing a variety of physical and spectroscopic techniques. The catalyst activities were evaluated through both CO conversion versus temperature and CO conversion versus time tests. The DRIFTS spectra were obtained on stream during the WGS reaction at increasing temperatures, from 303 to 573 K. Reduced ceria was the only active support and promoted the WGS reaction on surface bridging OH groups that react with CO to form formate intermediates. Pt/SiO₂ was more active than CeO₂ and catalyzed the WGS reaction through a monofunctional redox mechanism on metallic Pt sites. The CO conversion turnover rate was more than one order of magnitude greater on Pt/CeO₂ than on Pt/SiO₂ showing that the reaction proceeds faster via a bifunctional metal-support mechanism. Platinum on Pt/CeO₂ increased the concentration of OH groups by increasing the ceria reduction extent and also provided a faster pathway for the formation of formate intermediates in comparison to CeO₂ support. Pt/TiO₂ catalysts were clearly more active than Pt/CeO₂. The WGS reaction on Pt/TiO₂ was catalyzed via a bifunctional metal-support mechanism, probably involving the activation of CO and water on the metal and the support, respectively. The role of platinum on Pt/TiO₂ was critical for promoting the reduction of Ti⁴⁺ ions to Ti³⁺ which creates oxygen vacancies in the support to efficiently activate water.     

Water–gas shift reaction over Pt and Pt–CeOx supported on CexZr1−xO2

The water–gas shift (WGS) reaction was examined over Pt and Pt–CeO_x catalysts supported on Ce_xZr_1−xO₂ (Ce_0.05Zr_0.95O₂, Ce_0.2Zr_0.8O₂, Ce_0.4Zr_0.6O₂, Ce_0.6Zr_0.4O₂, Ce_0.7Zr_0.3O₂ and Ce_0.8Zr_0.2O₂) under severe reaction conditions, viz. 6.7 mol% CO, 6.7 mol% CO₂, and 33.2 mol% H₂O in H₂. The catalysts were characterized with several techniques, including X-ray diffraction (XRD), CO chemisorption, temperature-programmed reduction (TPR) with H₂, temperature-programmed oxidation (TPO), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and bright-field transmission electron microscopy (TEM). Among the supported Pt catalysts tested, Pt/Ce_0.4Zr_0.6O₂ showed the highest WGS activity in all temperature ranges. An improvement in the WGS activity was observed when CeO_x was added with Pt on Ce_xZr_1−xO₂ supports (x = 0.05 and 0.2) due to intimate contact between Pt and CeO_x species. Based on CO chemisorptions and TPR profiles, it has been found that the interaction between Pt species and surface ceria-zirconia species is beneficial to the WGS reaction. A gradual decrease in the catalytic activity with time-on-stream was found over Pt and Pt–CeO_x catalysts supported on Ce_xZr_1−xO₂, which can be explained by a decrease in the Pt dispersion. The participation of surface carbonate species on deactivation appeared to be minor because no improvement in the catalytic activity was found after the regeneration step where the aged catalyst was calcined in 10 mol% O₂ in He at 773 K and subsequently reduced in H₂ at 673 K.     

Effect of ZrO2 on the performance of Co–CeO2 catalysts for hydrogen production from waste-derived synthesis gas using high-temperature water gas shift reaction

In this study, highly active and stable CeO₂, ZrO₂, and Zr_(1-x)Ce_(x)O₂-supported Co catalysts were prepared using the co-precipitation method for the high-temperature water gas shift reaction to produce hydrogen from waste-derived synthesis gas. The physicochemical properties of the catalysts were investigated by carrying out Brunauer-Emmet-Teller, X-ray diffraction, CO-chemisorption, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and H₂-temperature-programmed reduction measurements. With an increase in the ZrO₂ content, the surface area and reducibility of the catalysts increased, while the interaction between Co and the support and the dispersion of Co deteriorated. The Co–Zr_0.4Ce_0·6O₂ and Co–Zr_0.6Ce_0·4O₂ catalysts showed higher oxygen storage capacity than that of the others because of the distortion of the CeO₂ structure due to the substitution of Ce⁴⁺ by Zr⁴⁺. The Co–Zr_0.6Ce_0·4O₂ catalyst with high reducibility and oxygen storage capacity exhibited the best catalytic performance and stability among all the catalysts investigated in this study.     

Preferential oxidation of CO in H2 stream on Au/CeO2–TiO2 catalysts

A series of Au catalysts supported on CeO₂–TiO₂ with various CeO₂ contents were prepared. CeO₂–TiO₂ was prepared by incipient-wetness impregnation with aqueous solution of Ce(NO₃)₃ on TiO₂. Gold catalysts were prepared by deposition–precipitation method at pH 7 and 65 °C. The catalysts were characterized by XRD, TEM and XPS. The preferential oxidation of CO in hydrogen stream was carried out in a fixed bed reactor. The catalyst mainly had metallic gold species and small amount of oxidic Au species. The average gold particle size was 2.5 nm. Adding suitable amount of CeO₂ on Au/TiO₂ catalyst could enhance CO oxidation and suppress H₂ oxidation at high reaction temperature (>50 °C). Additives such as La₂O₃, Co₃O₄ and CuO were added to Au/CeO₂–TiO₂ catalyst and tested for the preferential oxidation of CO in hydrogen stream. The addition of CuO on Au/CeO₂–TiO₂ catalyst increased the CO conversion and CO selectivity effectively. Au/CuO–CeO₂–TiO₂ with molar ratio of Cu:Ce:Ti = 0.5:1:9 demonstrated very high CO conversion when the temperature was higher than 65 °C and the CO selectivity also improved substantially. Thus the additive CuO along with the promoter and amorphous oxide ceria and titania not only enhances the electronic interaction, but also stabilizes the nanosize gold particles and thereby enhancing the catalytic activity for PROX reaction to a greater extent.     

Biohydrogen synthesis from catalytic steam gasification of furniture waste using nickel catalysts supported on modified CeO2

Present study evaluated the catalytic steam gasification of furniture waste to enhance the biohydrogen production. To do this, 10 wt% nickel loaded catalysts on the variety of supports (Al₂O₃, CeO₂, CeO₂-La₂O₃, and CeO₂–ZrO₂) were prepared by the novel solvent deficient method. The hydrogen selectivity (vol%) order of the catalysts was achieved as Ni/CeO₂–ZrO₂>Ni/CeO₂>Ni/Al₂O₃?Ni/CeO₂-La₂O₃. The best catalytic activity of Ni/CeO₂–ZrO₂ catalyst (~82 vol % H₂ at 800 °C) was ascribed to the smaller size of nickel crystals, finely dispersed Ni on the catalyst surface, and Ce_1-xZr_xO_2-δ solid solution. The role of Ce_1-xZr_xO_2-δ solid solution in Ni/CeO₂–ZrO₂ catalyst was observed as bi-functional; acceleration of water-gas-shift and oxidation of carbon reaction. The high resistance of Ni/CeO₂–ZrO₂ towards the coke formation showed its potential to establish a cost-effective commercial-scale biomass steam gasification process. This study is expected to provide a promising solution for the disposal of furniture wastes for production of clean energy (biohydrogen).     

Effect of oxygen addition on the water–gas shift reaction over Pt/CeO2 catalysts in microchannels – Results from catalyst testing and reactor performance in the kW scale

Wash-coated Pt/CeO₂, Pt/CeO₂/ZrO₂ and Pt/Cu/CeO₂ and Pt/CeO₂/Al₂O₃ based formulations were tested in sandwich type microreactors for water–gas shift (WGS) activity. At low reaction temperature of 260 °C, low conversion of carbon monoxide was initially observed which increased considerably upon the addition of air, a behaviour which was observed even after multiple cycles of start-up, operation with and without air and shut-down. At a higher reaction temperature of 400 °C air addition did not further improve the performance of the catalysts, which converted the carbon monoxide already close to equilibrium. One of the catalysts was incorporated into a larger reactor of kW scale and tested for its performance under conditions of WGS and oxygen enhanced WGS. The carbon monoxide conversion was increased by the air addition also on the larger reactor.     

Reduction reactivity of CeO2-ZrO2 oxide under high O2 partial pressure in two-step water splitting process

The O₂-releasing reaction under the air with the reactive ceramics of CeO₂-ZrO₂ oxides which can be applied to solar hydrogen production via a two-step water splitting cycle using concentrated solar thermal energy was investigated. CeO₂-ZrO₂ oxides were synthesized by polymerized complex method at different Ce:Zr molar ratio. The solid solubility of ZrO₂ in fluorite structure of CeO₂ was in good agreement with the initial content of Zr ions at the preparation in CeO₂-ZrO₂ oxide. The O₂-releasing reaction in air with CeO₂-ZrO₂ oxides was studied. Different solid solubility (0%, 10%, 20%, 30%) of ZrO₂ in CeO₂ were examined. The amount of O₂ gas evolved in the reaction with Ce_1−xZr_xO₂ (0 ? x ? 0.3) solid solutions was more than that with CeO₂, and the largest yield of 2.9 cm³/g was exhibited at x = 0.2 (Ce_0.8Zr_0.2O₂) for an O₂ release at 1500 °C in air. The reduced cerium ion in Ce_0.8Zr_0.2O₂ was about 11%, which is seven times higher than that with CeO₂. The optical absorption and luminescence spectra of the CeO₂-ZrO₂ oxide obtained before and after the O₂-releasing reaction suggest that the reduction of Ce⁴⁺ with formation of oxygen defect in the air. The enhancement of the O₂-releasing reaction with CeO₂-ZrO₂ oxide is found to be caused by an introduction of Zr⁴⁺, which has smaller ionic radius than Ce³⁺ or Ce⁴⁺, in the fluorite structure.     

Mechanistic aspects of the low temperature steam reforming of ethanol over supported Pt catalysts

The influence of the support of Pt catalysts for the reaction of steam reforming of ethanol at low temperatures has been investigated on Al₂O₃, ZrO₂ and CeO₂. It was found that the conversion of ethanol is significantly higher when Pt is dispersed on Al₂O₃ or ZrO₂, compared to CeO₂. Selectivity toward H₂ is higher over ZrO₂-supported catalyst, which is also able to decrease CO production via the water-gas shift reaction. Depending on catalyst employed, interaction of the reaction mixture with the catalyst surface results in the development of a variety of bands attributed to ethoxy, acetate and formate/carbonate species associated with the support, as well as by bands attributed to carbonyl species adsorbed on platinum sites. The oxidation state of Pt seems to affect catalytic activity, which was found to decrease with increasing the population of adsorbed CO species on partially oxidized (Pt^δ+) sites. Evidence is provided that the main reaction pathway ethanol dehydrogenation, through the formation of surface ethoxy species and subsequently acetaldehyde, which is decomposed toward methane, hydrogen and carbon oxides. The population of adsorbed surface species, as well as product distribution in the gas phase varies significantly depending on catalyst reactivity towards the WGS reaction.     

Electrocatalysts for bifunctional oxygen/air electrodes

Oxygen reduction and evolution have been studied with respect to the development of bifunctional air/oxygen electrode (BFE). Three groups of catalysts have been prepared: (i) Cu_xCo_3−xO₄ by thermal decomposition of mixed nitrate and carbonate precursors; (ii) thin films of Co–Ni–Te–O and Co–Te–O were deposited by vacuum co-evaporation of Co, Ni and TeO₂ and (iii) Co_xO_v/ZrO₂ films were obtained by electrochemical deposition.     

Photodeposition of AuNPs on metal oxides: Study of SPR effect and photocatalytic activity

Effect of photodeposition of AuNPs (gold nanoparticles) on TiO₂, CeO₂, Cu₂O and Fe₃O₄ supports has been illustrated on sacrificial donor based hydrogen evolution. The synthesized samples were characterized by diffuse reflectance spectroscopy (DRS), and transmission electron microscopy (TEM). Highest photocatalytic activity was exhibited by Au/TiO₂ followed by Au/Fe₃O₄, Au/CeO₂ and Au/Cu₂O. Au/TiO₂ under optimized conditions has shown significantly high photocatalytic activity under both UV–visible and visible radiation. Au/TiO₂ shows hydrogen evolution rate of 920 μmol h⁻¹ and 32.4 μmol h⁻¹ under UV–visible and visible radiation, respectively. Significant enhancement in hydrogen evolution rate under visible light is very encouraging and may be attributed to polydispersed nature of AuNPs wherein larger particles facilitate light absorption and the smaller function as catalytic sites. Further studies are in progress to study the influence of various parameters on photocatalytic activity of Au/TiO_2.     

Hydrogen production from the oxidative steam reforming of methanol over AuCu nanoparticles supported on Ce1-xZrxO2 in a fixed-bed reactor

Oxidative steam reforming of methanol over monometallic gold (Au) and bimetallic Au-copper (Cu) supported on ceria-zirconia (CeO₂ZrO₂) was examined over the temperature range of 200–400 °C in a fixed-bed reactor. The composition of CeO₂ZrO₂ supports was also studied for their catalytic activity. The Au/Ce_0.75Zr_0.25O₂ catalyst exhibited the highest methanol (CH₃OH) conversion level (96.7%) and hydrogen (H₂) yield (59.7%) due to the formation of a homogeneous Ce_1-xZr_xO₂ solid solution. When Cu was introduced in the Au catalysts, all of the bimetallic catalysts presented a better stability for CH₃OH conversion as well as H₂ yield in comparison to the monometallic catalysts, which was due to the partial electron transfer from Cu to Au metals. The performance of the AuCu/Ce_0.75Zr_0.25O₂ catalysts, which was evaluated under identical conditions, was ranked in the order: 3Au1Cu > 1Au3Cu > 1Au1Cu.     

Three-dimensional plasmonic photoanode of Co3O4 nanosheets coated onto TiO2 nanorod arrays for visible-light-driven water splitting

In this work, we report for the first time a plasmonic photoanode by decorating Au nanoparticles (NPs) onto two-dimensional (2D) Co₃O₄ nanosheets (NSs)/one-dimensional (1D) TiO₂ nanorod arrays (NRAs) (Au/Co₃O₄/TiO₂-NRAs) for enhanced visible-light photoelectrochemical (PEC) water splitting. In this plasmonic photoanode, TiO₂ NRAs act as an electron acceptor, plasmonic Au NPs and hierarchical Co₃O₄ NSs serve as visible-light harvesters. Light absorption shows that Au/Co₃O₄/TiO₂-NRAs heterojunction architectures exhibit greatly improved ability to harvest visible light due to the surface plasmon resonance (SPR) absorption of Au NPs and visible light harvesting ability of Co₃O₄ NSs. Spectroscopic measurements demonstrate that a type II band alignment is formed between Co₃O₄ and TiO₂. Benefiting from the SPR effect, type II band alignment and novel hierarchical architecture, plasmonic Au/Co₃O₄/TiO₂-NRAs photoanode shows remarkably enhanced visible-light PEC water splitting activity compared with Co₃O₄/TiO₂-NRAs and pristine TiO₂-NRAs photoanodes. Photocurrent density achieved by plasmonic photoanode is 37 and 1.2 times higher than those of TiO₂-NRAs and Co₃O₄/TiO₂-NRAs photoanodes, respectively. This work provides a promising strategy to highly enhance visible-light PEC water splitting activity of wide band-gap semiconductor-based photoelectrode materials.     

Factors determining gasoline soot abatement over CeO2–ZrO2-MnOx catalysts under low oxygen concentration condition

Soot oxidation under a low concentration O₂ (0.5% O₂/N₂) was investigated using CeO₂–ZrO₂-MnO_x mixed oxides with varied amounts of MnO_x, in order to gain low temperature catalytic activity and find out the main factors affecting the soot oxidation. The catalytic activity was remarkably improved over these catalysts compared to that of non-catalyst in such a low concentration of O₂. In particular, CeO₂–ZrO₂-MnO_x with 10% MnO_x doping (M10-CZ) showed the highest catalytic activity with its T₅₀ values of 340 °C under tight contact condition. The results of N₂ adsorption-desorption and X-ray diffraction (XRD) indicated that the textural and structural properties were not positive correlation with soot oxidation, are not the main factors affecting the catalytic activity of CeO₂–ZrO₂ and CeO₂–ZrO₂-MnO_x catalysts. The results of oxygen storage capacity (OSC), hydrogen-temperature programmed reduction (H₂-TPR), O₂ temperature program desorption (O₂-TPD), UV Raman spectroscopy (UV Raman) and X-ray photoelectron spectroscopy (XPS) testified that redox ability, oxygen storage capacity, oxygen desorption capacity at low temperature and surface active oxygen species are more important for soot oxidation. The enhancements of the catalytic behavior after MnO_x addition can be due to the improving of the adsorbed, activation and mobility of reactive oxygen species. In this work, these factors about generation and movement of reactive oxygen species are crucial for soot oxidation in a low oxygen concentration condition.     

Low temperature hydrogen production by catalytic steam reforming of methane in an electric field

Catalytic steam reforming of methane in an electric field (electroreforming) at low temperatures such as 423 K was investigated. Pt catalysts supported on CeO₂, Ce_xZr_1−xO₂ solid solution and a physical mixture of CeO₂ and other insulators (ZrO₂, Al₂O₃ or SiO₂) were used for electroreforming. Among these catalysts, Pt catalyst supported on Ce_xZr_1−xO₂ solid solution showed the highest activity for electroreforming (CH₄ conv. = 40.6% at 535.1 K). Results show that the interaction among the electrons, metal loading, and catalyst support was important for high catalytic activity on the electroreforming. Catalytic activity of the electroreforming increased in direct relation to the input current. Characterizations using X-ray diffraction (XRD), temperature programmed reduction with H₂ (H₂-TPR), and alternate current (AC) impedance measurement show that the catalyst structure is an important factor for activity of electroreforming.     

Bulk conduction and relaxation in [(ZrO2)1−x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions at intermediate temperatures

Bulk conduction and relaxation of the [(ZrO₂)_1−x(CeO₂)_x]_0.92(Y₂O₃)_0.08 (0 ≤ x ≤ 1) solid solutions were studied using impedance spectroscopy at intermediate temperatures (200-500 °C). The bulk conductivity as a function of x shows a “V-shape” variation which is a competitive effect of the defect associates and the lattice parameter. In the ZrO₂-rich region (x < 0.5) CeO₂ doping increases the concentration of defect associates which limits the mobility of the oxygen vacancies; in the CeO₂-rich region (x > 0.5) the increase of x increases the lattice parameter which enlarges the free channel for oxygen vacancy migration. Further analysis indicates the ionic radius of the tetravalent dopant determines the composition dependence of the ionic conductivity of the solid solutions. When doping YSZ with other tetravalent dopant with similar ionic radius with Zr⁴⁺, e.g., Hf⁴⁺, such “V-shape” composition dependence of the bulk conductivity cannot be observed.     

Influence of coexisting Al2O3 on the activity of copper catalyst for water–gas-shift reaction

Influence of coexisting Al₂O₃ on the catalytic activity for low-temperature water–gas-shift (LT-WGS) reaction over Cu catalyst was investigated. The catalytic activity of Cu/Al₂O₃ catalyst increased with decreasing mesopore size when S/C ratio was 2.2, whereas the catalytic activity with S/C ratio = 4.6 increased with increasing mesopore size. IR measurement combined with kinetic study suggested that the low catalytic activity of Cu/CeO₂ catalyst comes from the restriction of CO adsorption on Cu⁰ by bidentate-type carbonate formed on the strong basic site of CeO₂ support. On the other hand, it was found that bidentate-type carbonate was not formed on Cu/Al₂O₃ showing high catalytic activity for LT-WGS reaction.     

Reactive ceramics of CeO2–MOx (M=Mn,Fe, Ni,Cu) for H2 generation by two-step water splitting using concentrated solar thermal energy

The addition of MO_x (M: di- or tri-valent transition metal ion) into cerium dioxide (CeO₂) enhanced the ability of CeO₂ for the oxygen (O₂)-releasing reaction at lower temperature and swift hydrogen (H₂)-generation reaction. CeO₂–MO_x (M=Mn, Fe, Ni, Cu) reactive ceramics having high melting points were synthesized with the combustion method from their nitrates for solar H₂ production. The prepared CeO₂–MO_x samples were solid solutions between CeO₂ and MO_x with the fluorite structure through the X-ray diffractometry measurement. Two-step water-splitting reactions with CeO₂–MO_x reactive ceramics proceeded at 1573–1773 K for the O₂-releasing step and at 1273 K for the H₂-generation step by irradiation of infrared image furnace as a solar simulator. The amounts of O₂ evolved in the O₂-releasing reaction with CeO₂–MO_x increased with an increase in the reaction temperature. The amounts of H₂ evolved in the H₂-generation reaction with CeO₂–MO_x systems except for M=Cu were more than that of CeO₂ system after the O₂-releasing reaction at the temperatures of 1673 and 1773 K. The amounts of H₂ evolved in the H₂-generation reaction with CeO₂–MnO and CeO₂–NiO systems were more than those of CeO₂–Fe₂O₃, CeO₂–CuO and CeO₂ systems after the O₂-releasing reaction at the temperature of 1573 K. The amounts of evolved H₂ after the O₂-releasing reaction at the temperature of 1773 K in cm³ per gram of CeO₂–MO_x were 0.975–3.77 cm³/g. The O₂-releasing reaction at 1673 K and H₂-generation reaction at 1273 K with CeO₂–Fe₂O₃ proceeded with repetition of 4 times stoichiometrically.     

Inhibition of water-gas shift reaction activity of oxide-supported Pt catalyst by H2 and CO2

A catalyst composed of platinum-group metals supported on an oxide exhibits high activity in a low-temperature water-gas shift (LT-WGS) reaction; however, the reaction rate is greatly reduced when H₂ or CO₂, the product gases of the WGS reaction, are included in the reactant stream. In this study, we attempted to understand the origin of this activity inhibition by analyzing the kinetic data with in-situ CO-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The WGS reaction rate decreases more severely by H₂ than CO₂. The CO-DRIFTS spectra indicate that this can be explained by H₂ preoccupying the active sites for the WGS reaction. In addition, by comparing the kinetic data with the literature, it could be inferred that a similar inhibition mechanism is operating in other oxide-supported Pt catalysts. Considering this inhibition mechanism will be important for the development of catalysts with high WGS activity in reformate gas.     

Stable BaCe0.5Zr0.3Y0.16Zn0.04O3−δ thin membrane prepared by in situ tape casting for proton-conducting solid oxide fuel cells

Stable BaCe_0.5Zr_0.3Y_0.16Zn_0.04O_3−δ (BCZYZ) thin membrane was successfully prepared by in situ tape casting/co-firing method for proton-conducting solid oxide fuel cells. The starting powders were BaCO₃, CeO₂, ZrO₂, Y₂O₃, ZnO for electrolyte and BaCO₃, CeO₂, ZrO₂, Y₂O₃, ZnO, NiO, graphite for anode. The anode/electrolyte bi-layers were prepared by a simple multi-layer tape casting/co-firing method. The phase characterizations and microstructures were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The anode–electrolyte bi-layers were sintered at 1450 °C. The electrolytes were extremely dense with pure perovskite phase and the thickness was about 25 μm. The anodes were porous and no obvious reaction was found between NiO and BCZYZ. With LaSr₃Co_1.5Fe_1.5O_10−δ (LSCF)/BCZYZ as cathode, the open current voltage and maximum power density respectively, reached 1.00 V and 247 mW cm⁻² at 650 °C.