Herein, we present an innovative approach for transforming commonly available cellulose paper into a flexible and catalytic current collector for overall water splitting. A solution processed soak-and-coat method of electroless plating was used to render a piece of paper conducting by conformably depositing metallic nickel nanoparticles, while still retaining the open macroporous framework. Proof-of-concept paper-electrodes are realized by modifying nickel-paper current collector with model electrocatalysts nickel-iron oxyhydroxide and nickel-molybdenum bimetallic alloy through electrodeposition route. The paper-electrodes demonstrate exceptional activities towards oxygen evolution reaction and hydrogen evolution reaction, requiring overpotentials of 240 and 32 mV at 50 and −10 mA cm−2, respectively, even as they endure extreme mechanical stress. The generality of this approach is demonstrated by fabricating similar electrodes on cotton fabric, which also show high activity. Finally, a two-electrode paper-electrolyzer is constructed which can split water with an efficiency of 98.01%, and exhibits robust stability for more than 200 h.
B-site cation exsolution in perovskite oxide (ABO3) catalyst to surface decorated bimetallic nanoparticles facilitates the usually arduous trifunctional electrocatalytic activity towards oxygen reduction and water oxidation cum reduction reactions.
Perovskite oxides have emerged as promising oxygen electrocatalysts for fuel cells and batteries, yet their catalytic activity and long-term stability are under debate because of local surface alterations and instabilities under sustained oxidative potential. Interconnected particles (40 nm) of Ba 0.6 Sr 0.4 Co 0.79 Fe 0.21 O 2.67 (BSCF) are decorated by 10−50 wt % Ni 0.6 Fe 0.4 (OH) x [NiFe] layered double hydroxide (LDH) sheets via polyethylenimine linkage. This composite renders modulation of surface charges through Coulombic interaction and provides a leeway for electron mobility between the two components, which bestows relief to the BSCF surface from oxidative degradation. NiFe-LDH (25 wt %) bound to BSCF (BSCF/NiFe-25) is found to be the optimized bifunctional composite after considering the total overpotential of oxygen evolution and reduction reactions. With BSCF/NiFe-25 at the air electrode of a prototyperechargeable Zn−air battery, a low discharge−charge voltage gap (1.16 V at 10 mA cm −2 ), unaltered cyclic stability over 100 h, and an energy density of 776.3 mW•h•g Zn −1 are achieved. BSCF/NiFe-25 outperforms BSCF and is comparable to 20% Pt/C− RuO 2 cathodes in all the standard figures of merit. Our work presents a general strategy to circumvent the reconstructions of perovskite oxide surface under oxidative potentials, by creating highly active, stable, and inexpensive bifunctional composite electrocatalysts for future electrochemical energy storage and conversion devices.
Perovskite
oxides have attracted considerable attention as durable electrocatalysts
for metal–air batteries and fuel cells due to their precedence
in oxygen electrocatalysis in spite of the complexities involved with
their crystal structure, spin states, and physical properties. Here
we report optimization of the activity of a model perovskite system
La1–x
Sr
x
Co1–y
Fe
y
O3−δ (LSCF; x = 0.301, y = 0.298, and δ = 0.05–0.11) toward electrochemical
water oxidation (OER) by altering the calcination temperature of the
nonaqueous sol–gel synthesized nanoparticles (NPs). Our results
show that improved OER activity is the result of a synergism between
its morphology, surface area, electrical conductivity, and spin state
of the active transition metal site. With an eg orbital
occupancy of 1.26, the interconnected ∼90 nm LSCF NPs prepared
at 975 °C (LSCF-975) outperforms the other distinguishable LSCF
morphologies, requiring 440 mV overpotential to achieve 10 mA/cm2, a performance comparable to the best-performing perovskite
oxide electrocatalysts. While the interconnected NP morphology increases
the propensity of electronic conduction across crystalline grain boundaries,
the morphology-tuned high spin Co3+ ions increases the
probability of binding reaction intermediates at the available surface
sites. Density functional theory based work function modeling further
demonstrates that LSCF-975 is the most favorable OER catalyst among
others in terms of a moderate work function and Fermi energy level
facilitating the adsorption and desorption of reaction intermediates.
Five‐fold intertwined AgxNi1−x (x=0.01–0.25) heterogeneous alloy nanocrystal (NC) catalysts, prepared through unique reagent combinations, are presented. With only ca. 5 at % Ag (AgNi‐5), Pt‐like activity has been achieved at pH 14. To reach a current density of 10 mA cm−2 the extremely stable AgNi‐5 requires an overpotential of 24.0±1.2 mV as compared to 20.1±0.8 mV for 20 % Pt/C, both with equal catalyst loading of 1.32 mg cm−2. The turnover frequency (TOF) is as high as 2.1 H2 s−1 at 50 mV (vs. RHE). Site‐specific elemental analyses show the Ag:Ni compositional variation, where the apex and edges of the decahedra are Ag‐rich, thereby exposing Ni onto the faces to achieve maximum charge transport for an exceptional pH universal HER activity. DFT calculations elucidate the relative H‐atom adsorption capability of the Ni centers as a function of their proximity to Ag atom.
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