Cost-effective and highly active borohydride oxidation reaction (BOR) electrocatalysts are crucial for the advancement of direct borohydride fuel cells (DBFCs). Noble-metal electrocatalysts, such as Pd, are used as benchmark electrocatalysts because of their superior BOR activity. However, Pd suffers from catalyst poisoning because of strong binding with BH x intermediates at a high BOR overpotential, making it unsuitable for high DBFC performance, whereas Ni exhibits a low degree of catalyst poisoning because of a relatively weak binding of BH x intermediates. Density functional theory (DFT) calculations indicate a lowering of H-and OH-binding energies on bimetallic PdNi surfaces in comparison to their individual counterparts, thereby freeing more sites for BH 4 adsorption that is crucial for a high BOR rate. The as-synthesized bimetallic PdNi/C electrocatalyst exhibits higher current densities at a BH 4 concentration range of 50−500 mM than Pd/C and Ni/C. A DBFC unit with a pH-gradientenabled microscale bipolar interface employing PdNi/C, Pt/C, and H 2 O 2 as the anode, cathode, and oxidant, respectively, exhibits a power density of 466 ± 1.5 mW/cm 2 at 1.5 V, a peak power density of 630 ± 2 mW/cm 2 at 1.1 V, with an open-circuit voltage of 1.95 ± 0.01 V. Our bimetallic alloy electrocatalyst shows high DBFC performance, providing a pathway for the development of suitable BOR electrocatalysts.

The performance of fixed-gas unitized regenerative fuel cells (FG-URFCs) are limited by the bifunctional activity of the oxygen electrocatalyst. It is essential to have a good bifunctional oxygen electrocatalyst which can exhibit high activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this regard, Pt-Pb2Ru2O7-x is synthesized by depositing Pt on Pb2Ru2O7-x wherein Pt individually exhibits high ORR while Pb2Ru2O7-x shows high OER and moderate ORR activity. Pt-Pb2Ru2O7-x exhibits higher OER (η@10mAcm-2 = 0.25 ± 0.01 V) and ORR (η@-3mAcm-2 = -0.31 ± 0.02 V) activity in comparison to benchmark OER (IrO2, η@10mAcm-2 = 0.35 ± 0.02 V) and ORR (Pt/C, η@-3mAcm-2 = -0.33 ± 0.02 V) electrocatalysts, respectively. Pt-Pb2Ru2O7-x shows a lower bifunctionality index (η@10mAcm-2, OER− η@-3mAcm-2, ORR) of 0.56 V with more symmetric OER–ORR activity profile than both Pt (>1.0 V) and Pb2Ru2O7-x (0.69 V) making it more useful for the AEM (anion exchange membrane) URFC or metal-air battery applications. FG-URFC tested with Pt-Pb2Ru2O7-x and Pt/C as bifunctional oxygen electrocatalyst and bifunctional hydrogen electrocatalyst, respectively, yields a mass-specific current density of 715 ± 11 A/gcat-1 at 1.8 V and 56 ± 2 A/gcat-1 at 0.9 V under electrolyzer mode and fuel-cell mode, respectively. The FG-URFC shows a round-trip efficiency of 75% at 0.1 A/cm−2, underlying improvement in AEM FG-URFC electrocatalyst design.

No abstract

Significance The development of cost-effective batteries for long-duration grid scale energy storage will be accelerated using frameworks to rapidly screen and select battery components. Herein, we show that the solvent reorganization energy calculated from the Born equation (with reference to an electrolyte’s composition) is predictive of the electrolytes’ device level performance. This descriptor was found to correlate with key transport and kinetic properties over a range of electrolyte compositions and pH values, succinctly capturing the multicomponent interactions between the electrolyte salts and solvent. This enables the initial high-throughput screening of electrolyte candidates with minimal experimentation. Applied to aqueous redox flow batteries employing organic redox active species, we predict high-performance electrolyte compositions, enabling significantly enhanced device performance.

No abstract