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• Metal boride was firstly proposed as a novel catalyst for VRFB. • TiB 2 nanoparticles has low cost, large surface area and good electrical conductivity. • TiB 2 displays excellent electrocatalytic performance toward V3+/V2+ couple. • TiB 2 modified cell exhibits superior VRFB energy storage performance. [Display omitted] Transition metal borides have broad application prospects in the field of electrochemistry due to their excellent physicochemical stability and electrical conductivity. In this study, metal boride (titanium boride, TiB 2) was first proposed as a novel catalyst for V3+/V2+ in vanadium redox flow battery. Nano-TiB 2 exhibits large specific surface area and great electrical conductivity, and shows excellent catalytic performance in V3+/V2+ redox reaction. The performance of TiB 2 as negative catalyst for cell was further investigated. Compared with pristine cell, TiB 2 modified cell displays much higher discharge capacity (16.9 mA h) after 50 cycles and the incipient energy efficiency increases by 6.5%. The cell with TiB 2 as the negative electrode catalyst exhibits excellent rate performance at 50–150 mA cm−2. Voltage efficiency and energy efficiency of modified cell are 8.7% and 7.5% higher than those of pristine cell at 150 mA cm−2, respectively. In conclusion, this work reveals that nano-TiB 2 is a promising catalyst for enhancing the electrochemical performance toward V3+/V2+ redox reaction for vanadium redox flow battery. [ABSTRACT FROM AUTHOR]

As a novel type of proton conductor, BaHfO 3 -based proton conductor has a promising application potential, but its poor sinterability and low conductivity limit its application as hydrogen separation membrane materials. In this paper, In and Sn co-doping BaHfO 3 strategy was adopted to further optimize its sinterability and electrical conductivity. BaHf 0.9−x In x Sn 0.1 O 3−δ (x = 0.05–0.25) proton conductors were prepared by high temperature solid state method. The results of X-ray diffraction show that In3+ and Sn4+ have been successfully doped into the lattice to form a cubic perovskite structure. BaHf 0.7 In 0.2 Sn 0.1 O 3−δ (BHSI) was facilely sintered and reached a relative density above 96.25% at 1600 °C. The scanning electron microscope observation shows that the introduction of In3+ and Sn4+ can effectively improve the sinterability and increase the grain size of the sample. High relative density and big grain size allow reducing the volume fraction of grain boundaries and increasing the electrical conductivity of BHSI. The total conductivity of BHSI in wet air reaches 5.69 × 10−3 S cm−1 at 700 °C. In addition, BHSI also shows excellent chemical stability in pure H 2 and CO 2 , 200 ppm H 2 S and water steam, and boiling water. The obtained BHSI membranes were evaluated for hydrogen separation under a mode-pure protonic conductor with external short circuit. The hydrogen separation performance of BHSI membrane was tested systematically. Gas humidification on the feed side and sweep side can obviously increase the hydrogen permeation fluxes. BHSI membrane still maintains a stable hydrogen permeation performance, even 3% CO 2 and 100 ppm H 2 S was introduced into the feed gas, respectively. • The sinterability of barium hafnate-based proton conductors is improved by In and Sn co-doping. • BaHf 0.7 In 0.2 Sn 0.1 O 3−δ exhibits the improved conductivity due to decreasing bulk and grain boundary resistances. • The BaHf 0.7 In 0.2 Sn 0.1 O 3−δ membrane shows high performance for hydrogen separation. [ABSTRACT FROM AUTHOR]