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An MnNCN-Derived Electrocatalyst for CuWO4 Photoanodes

Davi, Martin, Mann, Markus, Ma, Zili, Schrader, Felix, Drichel, Andreas, Budnyk, Serhiy, Rokicinska, Anna, Kustrowski, Piotr, Dronskowski, Richard, Slabon, Adam
Langmuir 2018 v.34 no.13 pp. 3845-3852
X-ray diffraction, X-ray photoelectron spectroscopy, cobalt, cyanamides, electric current, electrodes, electrolytes, lighting, oxidation, oxygen production, pH, potassium phosphates, prices, toxicity
CuWO₄ is a photoanode candidate in neutral pH, and manganese-based oxygen evolution reaction electrocatalysts are of high interest due to their low price and low toxicity. Considering the unexplored chemistry of transition-metal carbodiimides/cyanamides for the PEC water oxidation, we investigated MnNCN as an electrocatalyst for CuWO₄ under AM 1.5G illumination in potassium phosphate electrolyte (pH 7). Surface functionalization of CuWO₄ photoanodes with MnNCN increased the photocurrent from 22 to 30 μA cm–² at 1.23 V vs RHE. Complementary structural analysis by means of XRD and XPS revealed that MnNCN forms a core–shell structure MnNCN@MnPOₓ in phosphate electrolyte and mimics a manganese phosphate electrocatalyst. As such, the surface chemistry of MnNCN significantly differs from previous studies on the cobalt analogue (CoNCN). A separately prepared MnNCN electrode developed a small but detectable photocurrent due to photogenerated holes inside the semiconducting carbodiimide core of the MnNCN@MnPOₓ structure.