Highly Active and Stable Cobalt-Free Hafnium-doped SrFe_0.9Hf_0.1O_3−δ Perovskite Cathode for Solid Oxide Fuel Cells

Sluggish oxygen reduction reaction (ORR) kinetics and chemical instability of cathode materials hinder the practical application of solid oxide fuel cells (SOFCs). Here we report a Co-free Hf-doped SrFe_0.9Hf_0.1O_3−δ (SFHf) perovskite oxide as a potential cathode focusing on enhancing the ORR activity and chemical stability. We find that SFHf exhibits a high ORR activity, stable cubic crystal structure, and improved chemical stability toward CO₂ poisoning compared to undoped SrFeO_3−δ. The SFHf cathode has a polarization area-specific resistance as low as 0.193 Ω cm² at 600 °C in a SFHf|Sm_0.2Ce_0.8O_1.9 (SDC)|SFHf symmetrical cell and has a maximum power density as high as 1.94 W cm^–2 at 700 °C in an anode-supported fuel cell (Ni+(ZrO₂)_0.92(Y₂O₃)_0.08 (YSZ)|YSZ|SDC|SFHf). The ORR activity maintains stable for a period of 120 h in air and in CO₂-containing atmosphere. The attractive ORR activity is attributed to the moderate concentration of oxygen vacancy and electrical conductivity, as well as the fast oxygen kinetics at the operation temperature. The improved chemical stability is related to the doping of the redox-inactive Hf cation in the Fe site of SrFeO_3−δ by decreasing oxygen vacancy concentration and increasing metal–oxygen bond energy. This work proposes an effective strategy in the design of highly active and stable cathodes for SOFCs

Highly Active and Stable Cobalt-Free Hafnium-doped SrFe_0.9Hf_0.1O_3−δ Perovskite Cathode for Solid Oxide Fuel Cells

Sluggish oxygen reduction reaction (ORR) kinetics and chemical instability of cathode materials hinder the practical application of solid oxide fuel cells (SOFCs). Here we report a Co-free Hf-doped SrFe_0.9Hf_0.1O_3−δ (SFHf) perovskite oxide as a potential cathode focusing on enhancing the ORR activity and chemical stability. We find that SFHf exhibits a high ORR activity, stable cubic crystal structure, and improved chemical stability toward CO₂ poisoning compared to undoped SrFeO_3−δ. The SFHf cathode has a polarization area-specific resistance as low as 0.193 Ω cm² at 600 °C in a SFHf|Sm_0.2Ce_0.8O_1.9 (SDC)|SFHf symmetrical cell and has a maximum power density as high as 1.94 W cm^–2 at 700 °C in an anode-supported fuel cell (Ni+(ZrO₂)_0.92(Y₂O₃)_0.08 (YSZ)|YSZ|SDC|SFHf). The ORR activity maintains stable for a period of 120 h in air and in CO₂-containing atmosphere. The attractive ORR activity is attributed to the moderate concentration of oxygen vacancy and electrical conductivity, as well as the fast oxygen kinetics at the operation temperature. The improved chemical stability is related to the doping of the redox-inactive Hf cation in the Fe site of SrFeO_3−δ by decreasing oxygen vacancy concentration and increasing metal–oxygen bond energy. This work proposes an effective strategy in the design of highly active and stable cathodes for SOFCs

Water Splitting with an Enhanced Bifunctional Double Perovskite

The rational design of highly active and durable electrocatalysts for overall water splitting is a formidable challenge. In this work, a double perovskite oxide, i.e., NdBaMn₂O_5.5, is proposed as a bifunctional electrode material for water electrolysis. Layered NdBaMn₂O_5.5 demonstrates significant improvement in catalyzing oxygen and hydrogen evolution reactions (OER and HER, respectively), in contrast to other related materials, including disordered Nd_0.5Ba_0.5MnO_3−δ as well as NdBaMn₂O_5.5−δ and NdBaMn₂O_5.5+δ (δ < 0.5). Importantly, NdBaMn₂O_5.5 has an OER intrinsic activity (∼24 times) and a mass activity (∼2.5 times) much higher than those of the benchmark RuO₂ at 1.7 V versus the reversible hydrogen electrode. In addition, NdBaMn₂O_5.5 achieves a better overall water splitting activity at large potentials (>1.75 V) and catalytic durability in comparison to those of Pt/C–RuO₂, making it a promising candidate electrode material for water electrolyzers. The substantially enhanced performance is attributed to the approximately half-filled e_g orbit occupancy, optimized O p-band center location, and distorted structure. Interestingly, for the investigated perovskite oxides, OER and HER activity seem to be correlated; i.e., the material achieving a higher OER activity is also more active in catalyzing HER

Image1_Effect of local application of bone morphogenetic protein -2 on experimental tooth movement and biological remodeling in rats.jpg

Background: This study attempts to detect the potential effects of local bone morphogenetic protein -2 (BMP-2) on orthodontic tooth movement and periodontal tissue remodeling.Methods: Forty adult SD rats were randomly divided into four groups: blank control group, unilateral injection of BMP-2 on the pressure side or tension side of orthodontic teeth and bilateral injection of BMP-2. Their maxillary first molar was moved by a 30 g constant force closed coil spring. 60 μL of BMP-2 with a concentration of 0.5 μg/mL was injected into each part at a time. In addition, three rats were selected as healthy control rats without any intervention. Fluorescent labeled BMP-2 was used to observe the distribution of exogenous BMP-2 in tissues. Micro-CT was used to measure the microscopic parameters of tooth displacement, trabecular bone and root absorption volume. Three different histological methods were used to observe the changes of tissue remodeling, and then the number of osteoclasts and the content of collagen fibers were calculated.Results: Compared with the blank control group, BMP-2 injection reduced the movement distance and increased the collagen fiber content and bone mass (p 0.05). In the case of bilateral injection of BMP-2, the osteogenesis is enhanced. Unilateral injection of BMP-2 did not promote root resorption, but double injection showed root resorption (p Conclusion: Our study does show that the osteogenesis of BMP-2 is dose-dependent rather than site-dependent when a certain amount of BMP-2 is applied around orthodontic teeth. Local application of BMP-2 around orthodontic teeth in an appropriate way can enhance bone mass and tooth anchorage without increasing the risk of root absorption volume. However, high levels of BMP-2 may cause aggressive root resorption. These findings are of great significance, that is, BMP-2 is an effective target for regulating orthodontic tooth movement.</p