Electrochemically assisted synthesis of three-dimensional FeP nanosheets to achieve high electrocatalytic activity for hydrogen evolution reaction

Iron phosphide (FeP) is a promising alternative catalyst for electrocatalytic hydrogen evolution reaction (HER) due to its low price, highly active catalytic sites and long-term anti-acid corrosion. Herein, we report a very facile strategy to fabricate novel FeP nanosheets as a HER electrocatalyst. Three-dimensional interconnected nanosheet structures of Fe₂O₃ (3D Fe₂O₃ NS) were directly exfoliated from metal Fe wires by alternating current (AC) voltage disturbance, and a simple subsequent phosphorization process could easily convert γ-Fe₂O₃ into FeP phase, which also maintained the 3D NS structure. Importantly, increasing the AC voltage resulted in the evolution of iron-containing nanostructures from nanoparticles to 2D nanosheets until the formation of 3D NS structure. Owing to the large specific surface area, enriched active sites and abundant hierarchical porous channels, as-prepared 3D FeP NS has exhibited significantly enhanced electrocatalytic HER activities such as a cathode current density of 10 mA cm⁻² at a small overpotential of 88 mV, low Tafel slope (47.7 mV dec⁻¹) and satisfactory long-term stability in acidic electrolyte. We expect that this simple and green synthetic strategy of transition metal phosphides will provide a promising prospect to innovate nonprecious HER electrocatalysts.     

Influence of the phosphorus source on iron phosphide nanoparticle synthesis for hydrogen evolution reaction catalysis

Iron phosphide (FeP) is in the spotlight as a hydrogen evolution reaction (HER) catalyst due to its cost efficiency, good catalytic activity, and stability within a wide pH range. However, there is still a need to synthesize FeP nanoparticles (NPs) with systematic analysis to improve their catalytic activity. Herein, we report FeP NPs synthesized with various phosphorus sources (TOP, trioctylphosphine; TPP, triphenylphosphite; TEAP, tris(diethylamino)phosphine; and TBP, tri-n-butylphosphine) via phosphorization reaction. We clearly demonstrate that the HER activity of the catalyst based on the FeP phase is dependent on the choice of phosphorus source used in the colloidal NP synthesis. Among the samples, FeP NPs synthesized with TPP achieved the highest HER activity with an overpotential of 76 mV at 10 mA cm⁻² in 0.5 M H₂SO₄. Our results reveal a critical aspect of colloidal synthesis to achieve enhanced catalytic activity in the synthesis of transition metal phosphide NPs.     

Hollow bimetallic M-Fe-P (M=Mn,Co, Cu) nanoparticles as efficient electrocatalysts for hydrogen evolution reaction

Searching for low-cost electrocatalysts with high activity towards the hydrogen evolution reaction (HER) is of great significance to enable large-scale hydrogen production via water electrolysis. In this study, by using inverse spinel MFe₂O₄(M = Mn, Fe, Co, Cu) nanoparticles (NPs) as the precursors, monodisperse bimetallic phosphide M-Fe-P NPs/C with hollow structures were readily obtained by a gas-solid annealing method. These hollow phosphide NPs displayed excellent HER activity in an acidic medium with a low loading amount of 0.2 mg cm⁻². In particular, the Co–Fe–P NPs/C shows highest HER activity that only requiring an overpotential of 97 mV to retain a current density of 10 mA cm⁻². A volcano relation between activity and incorporated elements was revealed. Incorporation of cation with high electronegativity stabilized the FeP active centres, while phase segregation resulted in the loss of activity for Cu–Fe–P NPs/C.     

Influence of hydrogen and carbon monoxide on reduction behavior of iron oxide at high temperature: Effect on reduction gas concentrations

The purposes of this study are to reduce Fe₂O₃ using hydrogen (H₂) and carbon monoxide (CO) gases at a high temperature zone (500 °C–900 °C) by focusing on the influence of reduction gas concentrations. Reduction behavior of hematite (Fe₂O₃) at high temperature was examined using temperature programmed reduction (TPR) under non-isothermal conditions with the presence of 10% H₂/N₂, 20% H₂/N₂, 10% CO/N₂, 20% CO/N₂ and 40% CO/N₂. The TPR_CO results indicated that the first and second reduction peaks of Fe₂O₃ at a temperature below 660 °C appeared rapidly when compared to TPR_H2. However, TPR_H2 exhibited a better reduction in which Fe₂O₃ entirely reduced to Fe at temperature 800 °C (20% H₂) without any remaining of wustite (FeO) whereas a temperature above 900 °C is needed for a complete reduction in 10% H₂/N₂, 10% and 20% CO/N₂. Furthermore, the reduction of hematite could be improved when increasing CO and H₂ concentrations since reduction profiles were shifted to a lower temperature. Thermodynamic calculation has shown that enthalpy change of reaction (ΔHr) for all phases transformation in CO atmosphere is significantly lower than in H₂. This disclosed that CO is the best reductant as it is a more exothermic, more spontaneous reaction and able to initiate the reduction at a much lower temperature than H₂ atmosphere. Nevertheless, the reduction of hematite using CO completed at a temperature slightly higher compared to H₂. It is due to the presence of an additional carburization reaction which is a phase transformation of wustite to iron carbide (FeO → Fe₃C). Carburization started at the end of the second stage reduction at 600 °C and 630 °C under 20% and 40% CO, respectively. Therefore, reduction by CO encouraged the formation of carbide, slower the reduction and completed at high temperature. XRD analysis disclosed the formation of austenite during the final stage of a reduction under further exposure with high CO concentration. Overall, less energy consumption needed during the first and second stages of reduction by CO, the formation of iron carbide and austenite were enhanced with the presence of higher CO concentration. Meanwhile, H₂ has stimulated the formation of pure metallic iron (Fe), completed the reduction faster, considered as the strongest reducing agent than CO and these are effective at a higher temperature. Proposed iron phase transformation under different reducing agent concentrations are as followed: (a) 10% H₂, 20% H₂ and 10% C; Fe₂O₃ → Fe₃O₄ → FeO → Fe, (b) 20% CO; Fe₂O₃ → Fe₃O₄ → FeO → Fe₃C → Fe and (c) 40% CO; Fe₂O₃ → Fe₃O₄ → FeO → Fe₃C → Fe → F,C (austenite).     

Metal-rich heterostructure of Ag-doped FeS/Fe2P for robust hydrogen evolution

The transition metal phosphides (TMPs) with highly active and low-cost are imperative electrocatalysts for hydrogen evolution reaction (HER). In particular, metal-rich interface engineering of iron phosphide could effectively modify the active sites for HER and accelerate the charge transfer, thus achieving the promoted efficiency. Herein, we report metal-rich heterostructure of Ag-doped Fe₂P shell attached to FeS core on Fe foams (FeS/Fe₂P–Ag@IF) for HER, which are synthesized by a simple hydrothermal method with subsequent low-temperature phosphorization. Notably, the phosphorization process simultaneously achieves the partial conversion of FeS to Fe₂P, and complete reduction of Ag₂S to Ag. Furthermore, the metal-rich structure of Fe₂P increases the active sites for hydrogen adsorption, which consequently contributes to hydrogen evolution. Simultaneously, the successful doping of metallic Ag enhanced the electroconductivity and the stability of the electrocatalyst. Benefiting from the ternary synergistic effect at FeS/Fe₂P–Ag@IF and metallic Ag doping, the optimal Ag-doped FeS/Fe₂P electrocatalyst exhibits a low overpotential of 214.9 mV at 100 mA cm^?2, even surviving at this large current density with long-term stability. This promising strategy involving metallic Ag doping may be a suitable option for the development of iron-based metal-rich phosphides heterostructured for HER.     

One-step synthesis of Co2P/N-P co-doped porous carbon composites derived from soybean derivatives as acidic and alkaline HER electrocatalysts

Developing inexpensive and efficient electrocatalysts for hydrogen evolution reaction (HER) in both acidic and alkaline mediums is of great significance to the hydrogen energy industry. Hereby, we prepared a mixture of precursors with homogeneous composition by using the chelating ability of soybean protein isolate (C and N source) and phytic acid (dopant and phosphating agent) with cobalt ions, and achieved one-step synthesis and construction of Co₂P/N–P co-doped porous carbon composite by carbonization at 800 °C. The as-synthesized Co₂P/NPPC-800 electrocatalyst exhibits low HER overpotentials of 121 and 125 mV at 10 mA cm^?2 in 0.5 M H₂SO₄ and 1.0 M KOH, which are close to those of the commercial Pt/C catalyst. Additionally, the NPPC substrate surrounding the Co₂P could diminish the corrosion during the HER, and Co₂P/NPPC-800 displays good stability and durability. Furthermore, this work offers a convenient synthesis strategy for phosphide/doped porous carbon composites in other electrochemical energy technologies.     

Fe2O3 nanoparticles immobilized on N and S codoped C as an efficient multifunctional catalyst for oxygen reduction reaction and overall water electrolysis

Currently, multifunctional electrocatalysts with superior performance are very vital for developing various clean and regenerated energy systems. Herein, an effective multifunctional electrocatalyst comprising Fe₂O₃ nanoparticles immobilized on N and S codoped C has been synthesized via heat-treatment of Fe(II) complex at 800 °C (denoted as Fe₂O₃/NS-C-800). Favorable features including the introduction of maghemite nanoparticles, N/S-codoping effect, and close contact between the Fe₂O₃ nanoparticles and NS-C ender the Fe₂O₃/NS-C-800 with high multifunctional catalytic performance. The onset potential (0.97 V) and half-wave potential (0.81 V) of the Fe₂O₃/NS-C-800 towards oxygen reduction reaction (ORR) are comparable to Pt/C (0.99 and 0.82 V). The Fe₂O₃/NS-C-800 also exhibits high oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity with low OER and HER overpotentials of 0.37 and −0.27 V at 10 mA cm⁻², respectively. In addition, higher ORR, OER and HER stabilities than Pt/C are observed for the Fe₂O₃/NS-C-800. More importantly, the assembled water electrolyzer using the Fe₂O₃/NS-C-800 as the anode and cathode exhibits a high stability at a water electrolysis current density of 10 mA cm⁻². The present study offers a new promising non-noble multifunctional catalyst for future application in renewable energy technologies.     

Catalytic supercritical water gasification of aqueous phase directly derived from microalgae hydrothermal liquefaction

Microalgae (N. chlorella) hydrothermal liquefaction (HTL) was conducted at 320 °C for 30 min to directly obtain original aqueous phase with a solvent-free separation method, and then the supercritical water gasification (SCWG) experiments of the aqueous phase were performed at 450 and 500 °C for 10 min with different catalysts (i.e., Pt-Pd/C, Ru/C, Pd/C, Na₂CO₃ and NaOH). The results show that increasing temperature from 450 to 500 °C could improve H₂ yield and TGE (total gasification efficiency), CGE (carbon gasification efficiency), HGE (hydrogen gasification efficiency), TOC (total organic carbon) removal efficiency and tar removal efficiency. The catalytic activity order in improving the H₂ yield was NaOH > Na₂CO₃ > None > Pd/C > Pt-Pd/C > Ru/C. Ru/C produced the highest CH₄ mole fraction, TGE, CGE, TOC removal efficiency and tar removal efficiency, while NaOH led to the highest H₂ mole fraction, H₂ yield and HGE at 500 °C. Increasing temperature and adding proper catalyst could remarkably improve the SCWG process above, but some N-containing compounds were difficult to be gasified. This information is valuable for guiding the treatment of the aqueous phase derived from microalgae HTL.     

Cobalt oxide as photocatalyst for water splitting: Temperature-dependent phase structures

This study investigated the best phases of cobalt oxide for the photochemical and photoelectrochemical (PEC) water-splitting reaction. Cobalt oxide was produced via a hydrothermal process of cobalt nitrate hexahydrate and then annealed at different temperatures from 450 °C to 950 °C. The Co₃O₄ phase was produced during pre-annealing and annealing at 450 °C. The mixed phase of Co₃O₄ and CoO was produced during annealing at 550 °C and 650 °C, and pure CoO was produced during annealing from 750 °C to 950 °C. The Co₃O₄ phase produced the highest photocurrent density with a value of 1.15 mA cm⁻² at a −0.4 V potential bias vs. Ag/AgCl. This value two times higher than that reported by other researchers at the same potential bias. Furthermore, the highest rate of hydrogen collected by Co₃O₄ was ~272.6 μmol h⁻¹ g⁻¹ after 8 h photocatalytic process. The amount of collected hydrogen was stable until 12 h of the process.     

Experimental study of the pyrolysis of waste bitumen for oil production

This work focuses on bitumen slow pyrolysis. Mass and energy yields of oil, solid and gas were obtained from pyrolysis experiments using a semi-batch reactor in a nitrogen atmosphere, under three non-isothermal conditions (maximum temperature: 450 °C, 500 °C and 550 °C). The effect of temperature on the product yields was discussed. The gas compositions were analysed using gas chromatography (GC) and the heating value of oil and solid residue was also measured. Using a thermo-gravimetric analyser, kinetic parameters were evaluated through Ozawa-Flynn-Wall (OFW) method. Results showed that oil yield is maximum at 500 °C (50%). Moreover, gas yield increased with increasing pyrolysis temperature from 18% to 36%. On the other hand, solid yield showed an opposite trend: it decreased from 39% to 32%. As regard energy yields, they showed a similar trend with the mass ones. H_2, CH₄, C₂H₄, C₂H₆ and C₃H₈ are the main components of the produced gas phase. It has been noticed that the recovery of bitumen to liquid oil through pyrolysis process had a great potential since the oil produced had high calorific value comparable with commercial fuels.     

Copper induced phosphide for enhanced electrochemical hydrogen evolution reaction

Research on highly efficient catalysts for electrochemical hydrogen evolution reaction (HER) remains a challenge. In this work, we successfully wrap copper (Cu) inside of copper phosphide (Cu₃P) nanoparticle to form a copper/copper phosphide (Cu/Cu₃P) core/shell structure attached on carbon nanotubes (CNTs) for enhanced HER activity in acid. The average size of the core/shell particles is around 25 nm, with about 5 nm of Cu₃P as the outer layer. The catalytic activity of the core/shell structure is significantly promoted compared to the metallic Cu and Cu₃P pure phases nanoparticles on CNTs, requiring overpotentials of 84 and 161 mV to achieve 10 and 100 mA cm⁻² of current density, respectively. The core/shell structure also presents high HER durability and stability, with the polarization curve overlapped after 5000 cycles of CVs and steady current density at 25 mA cm⁻² for as long as 10 h. To account for the promoted HER performance, the Cu/Cu₃P structure is fully investigated by physical and electrochemical characterizations and density functional theory (DFT) calculations. The DFT results depict that the neutralized the adsorption Gibbs free energy of hydrogen atoms (ΔG_H1) is induced by the electronic interactions between metallic Cu and phosphide phase.     

Influence of hydrogen and various carbon monoxide concentrations on reduction behavior of iron oxide at low temperature

The aims of this study are to produce Fe₃O₄ from Fe₂O₃ using hydrogen (H₂) and carbon monoxide (CO) gases by focusing on the influence of these gases on reduction of Fe₂O₃ to Fe₃O₄ at low temperature (below 500 °C). Low reduction temperature behavior was investigated by using temperature programmed reduction (TPR) with the presence of 20% H₂/N₂, 10% CO/N₂, 20% CO/N₂ and 40% CO/N₂. The TPR results indicated that the first reduction peak of Fe₂O₃ at low temperature appeared faster in CO atmosphere compared to H₂. Furthermore, reducibility of first stage reduction could be improved when increasing CO concentration and reduction rate were followed the sequence as: 40% CO > 20% CO > 10% CO > 10% H₂. All reduction peaks were shifted to higher temperature when the CO concentration was reduced. Although, initial reduction by H₂ occurred slower (first peak appeared at higher temperature, 465 °C) compared to CO, however, it showed better reduction with Fe₂O₃ fully reduced to Fe at temperature below 800 °C. Meanwhile, complete reduction happened at temperature above 800 °C in 10% and 20% CO/N₂. Thermodynamic calculation revealed that CO acts as a better reducer than H₂ as the enthalpy change of reaction (ΔH_r) is more exothermic than H₂ and the change in Gibbs free energy (ΔG) at 500 °C is directed to more spontaneous reaction in converting Fe₂O₃ to Fe₃O₄. Therefore, formation of magnetite at low temperature was thermodynamically more favorable in CO compared to H₂ atmosphere. XRD analysis explained the formation of smaller crystallite size of magnetite by H₂ whereas reduction of CO concentration from 40, 20 to 10% enhanced the growth of highly crystalline magnetite (31.3, 35.5 and 39.9 nm respectively). All reductants were successfully transformed Fe₂O₃ → Fe₃O₄ at the first reduction peak except for 10% CO/N₂ as there was a weak crystalline peak due to remaining unreduced Fe₂O₃. Overall, less energy consumption needed in reducing Fe₂O₃ to Fe₃O₄ by CO. This proved that CO was enhanced the formation of magnetite, encouraged formation of highly crystalline magnetite in more concentrated CO, considered better reducing agent than H₂ and these are valid at lower temperature.     

Boosting hydrogen evolution activity and durability of Pd–Ni–P nanocatalyst via crystalline degree and surface chemical state modulations

Developing efficient, durable, and economical electro-catalysts for large-scale commercialization of hydrogen evolution (HER) is still challenging. Herein, we report for the first time, to the best of our knowledge, a Pd-based ternary metal phosphide as an active and stable HER catalyst. The face-centered-cubic Pd–Ni–P nanoparticles (NPs) annealed at 400 °C show the best HER activity with a low overpotential of 32 mV to realize a current density of 10 mA cm⁻² and a high mass activity of 1.23 mA μg⁻¹_Pd, superior to Pd NPs, Pd–P NPs, Pd–Ni NPs, and Pd–Ni–P NPs annealed under different temperatures. Moreover, this catalyst is also highly stable during 20 h of continuous electrolysis. Notably, the easily fabricated Pd–Ni–P NPs are among the most active Pd-based HER catalysts. This work indicates that Pd-based metal phosphides could be potentially applied as a type of practical HER catalyst and might inform the fabrication of analogous materials for hydrogen-related applications.     

Optimal preparation of molybdenum phosphide cocatalyst for efficient dye-sensitized photocatalytic hydrogen evolution

Searching for non-noble-metal cocatalyst for hydrogen evolution in photocatalytic water–splitting has attracted much attention. Herein, molybdenum phosphide (MoP) as an efficient and stable cocatalyst was prepared in a facile phosphorization process at relatively low temperatures under N₂ atmosphere, and the effect of preparation temperature (300–500 °C) was studied. Using Eosin Y (EY) and the prepared sample as catalyst (sensitizer) and cocatalyst, respectively, the photocatalytic activity for hydrogen evolution was investigated in aqueous trimethylamine (TMA) solution under visible light irradiation (λ ≥ 420 nm). MoP prepared at 400 °C (MoP-400) exhibits the highest sensitization activity and superior stability, and the maximal apparent quantum yield (AQY) for hydrogen evolution is up to 48.0% at 420 nm, much higher than the most reported data for MoP-based photocatalysts. The highest activity can be attributed to the highest P content in MoP-400 and the rapidest electron transfer between photoexcited EY and MoP-400. The possible mechanism was discussed.     

Effect of Fe2P on the electron conductivity and electrochemical performance of LiFePO4 synthesized by mechanical alloying using Fe3+ raw material

LiFePO₄ and LiFePO₄/Fe₂P composites have been produced using raw Fe₂O₃ materials by mechanical alloying (MA) and subsequent firing at 900 °C. The LiFePO₄ prepared by firing at 900 °C for 30 min showed a maximum discharge capacity of 160 mAh g⁻¹ at C/20, which is at a higher capacity and improved cell performance compared with the LiFePO₄ prepared using for a longer firing times. LiFePO₄/Fe₂P composites have been synthesized by the reduction reaction of phosphate in excess of carbon. By transmission electron microscopy (TEM) and scanning electron microscopy (SEM) it was determined that the LiFePO₄ phase was agglomerated with a primary particle size of 40–50 nm around the surface of Fe₂P with particle size of 200 nm. The electronic conductivity of the LiFePO₄/Fe₂P composite increased in proportion with the amount that the Fe₂P phase and discharge capacity increased during the cycling. The sample containing 8% of Fe₂P in LiFePO₄/Fe₂P composite showed a high discharge capacity and rate capability at high current.     

Mechanisms of synthesis gas production via thermochemical cycles over La0·3Sr0·7Co0·7Fe0·3O3

La_0·3Sr_0·7Co_0·7Fe_0·3O₃ (LSCF3773) was chosen as an oxygen carrier material for synthesis gas production and synthesized using ethylene-diamine-tetra-acetic acid (EDTA) citrate-complexing method. LSCF exhibited a pure cubic structure where 110 and 100 plane diffractions were active for CO₂ splitting, while 111 was more favored by H₂O splitting. Overall oxygen storage capacity (OSC) of LSCF was 4072 μmol/g_cat. During the reduction process, regular cations (Co⁴⁺, Fe⁴⁺), polaron cations (Co³⁺, Fe³⁺) and localized cations (Co²⁺, Fe²⁺) were achieved when the LSCF was reduced at 500, 700 and 900 °C, respectively. The strength of the active sites depended on reduction temperatures. An increase in oxidation temperature enhanced H₂ production at temperature ranging from 500 °C to 700 °C while effected CO production at 900 °C. H₂O and CO₂ was competitively split during the oxidation step, especially at 700 °C. The activation energy of each reaction was ordered as; CO₂ splitting > H₂O splitting > CO₂ adsorption, supporting the above evidence where H₂ and CO production were found to increase when the operating temperature was increased.     

Studies on reduction of chromium doped iron oxide catalyst using hydrogen and various concentration of carbon monoxide

Chemical reduction behaviour of 3% chromium doped (Cr–Fe₂O₃) and undoped iron oxides (Fe₂O₃) were investigated by using temperature programmed reduction (TPR). The reduced phases were characterized by X-ray diffraction spectroscopy (XRD). The reduction processes were achieved with 10% H₂ in nitrogen (%, v/v), 10% and 20% of carbon monoxide (CO) in nitrogen (%, v/v). In hydrogen atmosphere, the TPR results indicate that the reduction of Cr–Fe₂O₃ and Fe₂O₃ proceed in three steps (Fe₂O₃ → Fe₃O₄ → FeO → Fe) with Fe₃O₄ and FeO as intermediate states. A complete reduction to metallic iron for both samples occurred at 900 °C. As for CO reductant, the profiles show the reduction of Fe₂O₃ also proceeded in three steps with a complete reduction occurs at 900 °C in 10% CO with no sign of carbide formation. Nevertheless, a 20% CO was able to reduce the completely at lower temperature at 700 °C and there is a formation of iron carbide at 500 °C but the carbide disappeared as the reduction temperature increase. Meanwhile in 10% CO atmosphere, Cr–Fe₂O₃ shows a better reducibility compared to Fe₂O₃ with a complete reduction at 700 °C, which is 200 °C lower than Fe₂O₃. A Cr dopant in the Fe₂O₃ can lead to formation of various forms of iron carbides such as F₂C, Fe₅C₂, Fe₂₃C₆ and Fe₃C as the CO concentration was increased to 20%. The transformation profile of iron phases during carburization follows the following forms, Fe₂O₃ → Fe₃O₄ → iron carbides (Fe_xC). The XRD pattern shows the diffraction peaks of Cr–Fe₂O₃ are more intense with improved crystallinity for the characteristic peaks of Fe₂O₃ compare to undoped Fe₂O₃. No visible sign of chromium particles peaks in the XRD spectrum that indicates the Cr particles loaded onto the iron oxide are well dispersed. The uniform dispersion with no sign of sintering effects of the Cr dopant on the Fe₂O₃ was confirmed by FESEM. The study shows that Cr dopant gives a better reducibility of iron oxide but promotes the formation of carbides in an excess CO concentration.     

Effects of carbon coating and iron phosphides on the electrochemical properties of LiFePO4/C

Carbon coated LiFePO₄ (LiFePO₄/C) with different contents of high electron conductive iron phosphide phase was synthesized by an aqueous sol–gel method in a reductive sintering atmosphere. Different synthesis parameters were used for adjusting the microstructure and phase compositions of the products. The effects of the carbon coating and iron phosphides on the electrochemical properties of the LiFePO₄/C electrodes were studied by means of testing the discharge capacities at rates of 0.1–5C (1C = 170 mAh g⁻¹) and analyzing the CV curves. The results show that carbon coating in a content of 1.5 wt.% derived from the carbon source of ethylene glycol greatly decreases the particle size of LiFePO₄ in one order in the specific surface area, and significantly improves the rate capability of LiFePO₄. The effect of the content of FeP on the capacity of the carbon coated LiFePO₄ was different at different discharge rates. Increasing the content of FeP from 1.2 to 3.7 wt.% slightly decreases the capacity of LiFePO₄/C at low discharge rate (0.1C and 1C), but obviously increases the capacity of LiFePO₄/C when the discharge rate is increased to 5C. For the carbon free sample, even it also has 1.8 wt.% FeP, it still possesses poor capacity due to the large particle size of LiFePO₄ and the lack of conductivity. And too much iron phosphides lowers the discharge capacity of the electrode since they are inert for the deinsertion/insertion of lithium ion.     

Understanding reactions between water and steelmaking slags: Iron distribution,hydrogen generation,and phase transformations

Environmentally friendly energy harvesting can be achieved by the H₂O thermochemical treatment of steelmaking slags. Hot slag from steel manufacturing is used as a sacrificial material to produce H₂ in a stream of steam. In parallel, this process enhances the magnetic properties of the slag, benefitting the Fe recovery. In this work, the occurrence states of different iron species in slags, as well as their reactivity and phase transformations in H₂O, were investigated. The results showed that Fe²⁺ was mainly distributed in olivine (Ca, Fe, Mg, Mn)₂SiO₄ when the basicity was low. As the basicity increased, a gradual enrichment of Fe²⁺ in RO phase (divalent oxides solid solution, R = Fe, Mg, Mn etc.) was observed. In addition to steelmaking slags, the H₂O splitting reactions of synthetic model iron compounds, RO phase (Mg_1–xFe_xO, x = 0.36, 0.63, 0.77) and kirschsteinite (CaFeSiO₄) were also tested. RO phase exhibited fast kinetics, with its activity proportional to the FeO content. Oxidation of the magnesia-rich RO phase resulted in the phase segregation of iron-depleted magnesiowüstite (Mg,Fe_depleted)O and iron-rich spinel (Mg,Fe_rich)₃O₄. The H₂O splitting of CaFeSiO₄ suffered from extremely low kinetics below 900 °C, which could be enhanced by raising the temperature. The H₂ production capacity of steelmaking slags was strongly affected by the basicity, which improved when more Fe²⁺ existed as RO phase rather than CaFeSiO₄. After oxidation in steam at 850 °C, the slag sample with a basicity of 1.83 produced 29.3 cm³?g^?1_material hydrogen at 850 °C for 60 min, with a conversion ratio of 80.1%.     

Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) and La0.6Ba0.4Co0.2Fe0.8O3−δ (LBCF) cathodes prepared by combined citrate-EDTA method for IT-SOFCs

The potential candidates for IT-SOFCs cathode materials, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) and La_0.6Ba_0.4Co_0.2Fe_0.8O_3−δ (LBCF), were synthesized by the combined citrate-EDTA method. The BSCF and LSCF aqueous precursors solutions were prepared from Sr(NO₃)₂, Ba(NO₃)₂, La(NO₃)₃·6H₂O, Co(NO₃)₂·6H₂O, Fe(NO₃)₃·9H₂O, citric acid and EDTA-NH₃. BSCF precursor solutions with different pH values were dried at 130 °C and subsequently calcined at various temperatures. Symmetrical electrochemical cells consisting of porous BSCF or LBCF electrodes and a GDC electrolyte were fabricated by the screen-printing technique, and the cathode performance of the interfaces between the porous electrode (BSCF or LBCF) and GDC electrolyte was investigated at intermediate temperatures (500–700 °C) using AC impedance spectroscopy. The pH value of the precursor solution did not affect the phase evolution behavior of the BSCF powder. On the other hand, it appears that a low pH value results in the calcined BSCF powder having a more porous microstructure. The cathode performances of the BSCF and LBCF electrodes were sensitive to the powder preparation conditions. The BSCF electrode prepared from the precursor solution with a pH value of 8 showed low polarization resistance, and its area specific resistances (ASR) were 1.1, 0.15 and 0.035 Ω cm² at 500, 600 and 700 °C, respectively. On the other hand, the cathode polarization resistances of the LBCF electrode were slightly higher than those of the BSCF electrode.