Cobalt-Imidazoles Passivated [alpha]-Fe.sub.2O.sub.3 Photoanode for Enhanced Photoelectrochemical Water Oxidation

Two types of cobalt imidazole complexes, e.g. cobalt 2-methylimidazole (Co-MIm) and cobalt 1-ethylimidazole (Co-EIm), are adopted as surface passivation agents to modify the Sn-doped [alpha]-Fe.sub.2O.sub.3 nanorods (Sn-Fe.sub.2O.sub.3 NRs) photoanode by a facile impregnation method. Systematic characterizations are performed and the fabricated photoanodes are applied to photoelectrochemical (PEC) water oxidation. Interestingly, the cobalt imidazoles nanosheets are embedded into the Sn-Fe.sub.2O.sub.3 NRs film to form crack-like gaps and NRs bundles on the surface of the composite photoanodes, e.g. Co-MIm@Sn-Fe.sub.2O.sub.3 and Co-EIm@Sn-Fe.sub.2O.sub.3. With simulated sunlight irradiation and an applied potential of 1.23 V (vs. RHE), the photocurrent densities of the Co-EIm@Sn-Fe.sub.2O.sub.3 and Co-MIm@Sn-Fe.sub.2O.sub.3 reach 0.81 mA/cm.sup.2 and 0.61 mA/cm.sup.2 with enhanced stability, respectively, compared with 0.36 mA/cm.sup.2 of the Sn-Fe.sub.2O.sub.3. The gaps and bundles on the surface of the composite photoanodes make the surface rougher and improve their light absorption ability. Moreover, the cobalt imidazoles as passivation agents can effectively inhibit surface states from capturing charge carriers, reduce charge recombination and facilitate charge transfer, thus improving the PEC performance. Notably, it is found that the cobalt imidazole with a longer alkyl chain, e.g. Co-EIm, is more effective than the Co-MIm. Graphical