The development of upscalable oxygen evolving electrocatalysts from earth-abundant metals able to operate in neutral or acidic environments and low overpotentials remains a fundamental challenge for the realization of artificial photosynthesis. In this study, we report a highly active phase of heterobimetallic cyanide-bridged electrocatalysts able to promote water oxidation under neutral, basic (pH < 13), and acidic conditions (pH > 1). Cobalt–iron Prussian blue-type thin films, formed by chemical etching of Co­(OH)1.0(CO3)0.5·nH2O nanocrystals, yield a dramatic enhancement of the catalytic performance toward oxygen production, when compared with previous reports for analogous materials. Electrochemical, spectroscopic, and structural studies confirm the excellent performance, stability, and corrosion resistance, even when compared with state-of-the-art metal oxide catalysts under moderate overpotentials and in a remarkably large pH range, including acid media where most cost-effective water oxidation catalysts are not useful. The origin of the superior electrocatalytic activity toward water oxidation appears to be in the optimized interfacial matching between catalyst and electrode surface obtained through this fabrication method.

Tuning the donor density and the surface state density of hematite multilayer nanowire photoanodes.

A facile and low-cost method is presented to synthesize graphite/PEDOT/MnO2 composites with controlled network structures on commercial supercapacitor separator (CSS) membranes for high-performance supercapacitors, in which pencil lead and a cellulose-based commercial supercapacitor separator membrane were applied as the graphite source and the flexible substrate, respectively. The dependence of PEDOT and MnO2 loading on the structural formation, the electrochemical performance of the hybrid electrode, and the formation mechanism of MnO2 nanowires are systematically investigated. The optimized electrode possesses a high areal capacitance of 316.4 mF/cm(2) at a scan rate of 10 mV/s and specific capacitance of 195.7 F/g at 0.5 A/g. The asymmetric supercapacitor device assembled using optimized CSS/Graphite/PEDOT/MnO2 electrode and activated carbon electrode exhibits a high energy density of 31.4 Wh/kg at a power density of 90 W/kg and maintains 1 Wh/kg at 4500 W/kg. After 2000 cycles, the device retains 81.1% of initial specific capacitance, and can drive a mini DC-motor for ca. 10 s. The enhanced capability of the CSS-based graphite/PEDOT/MnO2 network electrode has high potential for low-cost, high-performance, and flexible supercapacitors.

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For the design of a beneficial device structure, in which both electrodes are exposed to the same medium, and considering that the hydrogen evolution is most efficiently carried out in acidic electrolyte and the advantages of the proton exchange membrane, a robust photoanode would be highly desirable. [10][11][12][13][14][15] Nonetheless the development of an efficient and affordable photoanode, which is stable in acidic electrolyte, imposes a great challenge and limits the large-scale implementation of economically viable PEC water-splitting. In light of this challenge, much attention has been drawn to the development of efficient and affordable photoanode systems adapted to acidic electrolytes.Hematite is arguably the most desirable photoanode material. On one hand, its relatively small bandgap of 1.9-2.1 eV and its suitably aligned valence band level perfectly match the thermodynamic energy requirements needed to drive water oxidation. [4,10] On the other hand, it is made from the most abundant transition metal on Earth crust, iron. Unfortunately, the bare hematite surface is catalytically very poor, and therefore requires modification with water-oxidation catalysts (WOCs) in order to extract the thermodynamic power stored when light is absorbed. State-of-the-art water-oxidation catalysts (WOCs) in acidic electrolytesusually contain expensive noble metals such as ruthenium and iridium. However, they too expensive to be implemented broadly in semiconductor photoanodes for photoelectrochemical (PEC) water splitting devices. Here, an Earth-abundant CoFe Prussian blue analogue (CoFe-PBA) is incorporated with core-shell Fe 2 O 3 /Fe 2 TiO 5 type II heterojunction nanowires as composite photoanodes for PEC water splitting. Those deliver a high photocurrent of 1.25 mA cm −2 at 1.23 V versus reversible reference electrode in acidic electrolytes (pH = 1). The enhancement arises from the synergic behavior between the successive decoration of the hematite surface with nanolayers of Fe 2 TiO 5 and then, CoFe-PBA. The underlying physical mechanism of performance enhancement through formation of the Fe 2 O 3 /Fe 2 TiO 5 / CoFe-PBA heterostructure reveals that the surface states' electronic levels of hematite are modified such that an interfacial charge transfer becomes kinetically favorable. These findings open new pathways for the future design of cheap and efficient hematite-based photoanodes in acidic electrolytes.