Theoretical insights into metal-doped nanostructured hematite catalyst supported by graphene underlayer for photoelectrochemical water splitting applications

Catalysis is pivotal in the production of green hydrogen through water splitting to meet the goal of carbon neutrality. Hematite (Fe2O3) is an excellent catalyst and benchmarked photoanode materials in photoelectrochemical water splitting. Among the metal dopants, aluminum (Al) substitution in hematite is found intrinsically. In this study, we investigate Al doped nanostructured hematite as a photoanode material and a catalyst in water oxidation mechanism using density functional theory+ U methodology. We have found that Al doping in hematite monolayer leads to unfavorable increase in theoretical overpotential value by 0.19 V. To improve the efficiency of oxygen evolution reaction, we consider heterostructuring of Al doped nanostructured hematite with pristine graphene and nitrogen (N) doped graphene as an underlayer material. Nitrogen doped graphene underlayer leads to the lowest overpotential value of 0.54 V compared to Al doped hematite catalyst (0.96 V) and graphene-Al doped hematite catalyst (0.63 V). The work function is notably reduced after nitrogen doping by 1.41 eV and 1.12 eV as compared to graphene-Al doped hematite and Al doped hematite, respectively. Charge density difference and Bader charge analysis confirm that nitrogen doped graphene underlayer induces delocalized charge density and lowers the activity of the surface states in the *O intermediate. Nitrogen doped graphene-Al doped hematite heterostructure has nearly zero band gap and has the highest cumulative probability of charge transport at photoanode’s surface. Our theoretical study provides mechanistic insights into improving the catalytic efficiency of Al doped nanostructured hematite by heterostructuring with pristine and N doped graphene.