Phase engineering of a donor-doped air electrode for reversible protonic ceramic electrochemical cells

Reversible protonic ceramic electrochemical cells(R-PCECs)demonstrate great feasibility for efficient energy storage and conversion.One critical challenge for the development of R-PCECs is the design of novel air electrodes with the characteristics of high catalytic activity and acceptable durability.Here,we report a donor doping of Hf into the B-site of a cobalt-based double perovskite with a nominal formula of PrBa_(0.8)Ca_(0.2)Co_(1.9)Hf_(0.1)O_(5tδ)(PBCCHf_(0.1)),which is naturally reconfigured to a double perovskite PrBa_(0.8-x)Ca_(0.2)Co_(1.9)Hf_(0.1)-xO5tδ(PBCCHf_(0.1)-x)backbone and nano-sized BaHfO3(BHO)on the surface of PBCCHf_(0.1)x.The air electrode demonstrates enhanced catalytic activity and durability(a stable polarization resistance of 0.269Ωcm2 for~100 h at 600℃),due likely to the fast surface exchange process and bulk diffusion process.When employed as an air electrode of R-PCECs,a cell with PBCCHf_(0.1) air electrode demonstrates encouraging performances in modes of the fuel cell(FC)and electrolysis(EL)at 600℃:a peak power density of 0.998 W cm^(-2)and a current density of1.613 A cm^(-2)at 1.3 V(with acceptable Faradaic efficiencies).More importantly,the single-cell with PBCCHf_(0.1) air electrode demonstrates good cycling stability,switching back and forth from FC mode to EL mode0.5 A cm^(-2)for 200 h and 50 cycles.

Self-screening of the polarized electric field in wurtzite gallium nitride along[0001]direction

The strong polarization effect of GaN-based materials is widely used in high-performance devices such as white-lightemitting diodes(white LEDs),high electron mobility transistors(HEMTs),and GaN polarization superjunctions.However,the current researches on the polarization mechanism of GaN-based materials are not sufficient.In this paper,we studied the influence of polarization on electric field and energy band characteristics of Ga-face GaN bulk materials by using a combination of theoretical analysis and semiconductor technology computer-aided design(TCAD) simulation.The selfscreening effect in Ga-face bulk GaN under ideal and non-ideal conditions is studied respectively.We believe that the formation of high-density two-dimensional electron gas(2 DEG) in GaN is the accumulation of screening charges.We also clarify the source and accumulation of the screening charges caused by the GaN self-screening effect in this paper and aim to guide the design and optimization of high-performance GaN-based devices.

Ultrahigh electrostrain with excellent fatigue resistance in textured Nb^(5+)-doped(Bi_(0.5)Na_(0.5))TiO3-based piezoceramics

(Bi_(0.5)Na_(0.5))TiO_(3)(BNT)-based lead-free piezoceramics exhibit excellent electric field-induced strain(electrostrain)properties,but often suffer from large hysteresis and poor fatigue resistance,which strongly limit their applications.Here,<00l>textured Nb5+-doped 0.8(Bi_(0.5)Na_(0.5))TiO_(3)–0.2(Bi_(0.5)K_(0.5))TiO_(3)(0.8BNT–0.2BKT)ceramics with a high degree of texturing(~80%)were prepared by the reactive template grain growth(RTGG)method using Bi4Ti3O12 as a template.By the combination of donor doping in the B-site and the RTGG method,the electrostrain performance achieves a significant enhancement.A high electrostrain of 0.65%and a piezoelectric coefficient(*33 d)of 1083 pm/V with reduced hysteresis at an electric field of 6 kV/mm are obtained.No electrostrain performance degradation is observed after unipolar electric field loading of 10^(5)cycles,showing excellent fatigue endurance.These results indicate that the texturing BNT-based lead-free piezoceramics by the RTGG method is a useful approach to developing eco-friendly actuators.