Density functional theory (DFT) calculations were performed to study the mechanism of carbon dioxide (CO 2 ) reduction to carbon monoxide (CO) and methanol (CH 3 OH) on CeO 2 (110) surface. CO 2 dissociates to CO on interacting with the oxygen vacancy on reduced ceria surface.The oxygen atom heals the vacancy site and regenerates the stoichiometric surface via a redox mechanism with intrinsic activation and reaction energies of 259.2 kJ/mole and 238.6 kJ/mole respectively. Lateral interaction of oxygen vacancies were studied by the generation of two oxygen vacancies per unit of CeO 2 surface. Compared to a single isolated vacancy, the activation and reaction energies of CO 2 dissociation on a di-vacancy were approximately reduced to half of its value. Hydrogen atom co-adsorbed on the surface was observed to assist CO 2 dissociation by forming a carboxyl intermediate, CO 2 +H→COOH (∆E act = 39.0 kJ/mole, ∆H = -69.2 kJ/mole) which on subsequent dissociation produces CO via the redox mechanism. On hydrogenation, CO is likely to produce methanol. The energetics of CO hydrogenation to produce methanol showed exothermic steps with activation barriers comparable to the DFT calculations reported for Cu (111) and CeO 2-x /Cu(111) interface. While on the stoichiometric surface, COOH dissociation COOH→CO+OH (∆E act = 55.6 kJ/mole, ∆H =5.7 kJ/mole) is likely to be difficult as compared to rest of the elementary steps, whereas on the reduced surface the energetics of the same step were significantly lowered (∆E act = 47.4 kJ/mole, ∆H = -80.4 kJ/mole). In comparison, hydrogenation of methoxy, H 3 CO+H→H 3 COH, appears to be relatively difficult (∆E act = 58.7 kJ/mole) on the reduced surface.

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Reduced graphene oxide (RGO)-supported bismuth ferrite (BiFeO3) (RGO–BFO) nanocomposite is synthesized via a two-step chemical route for photoelectrochemical (PEC) water splitting and photocatalytic dye degradation. The detailed structural analysis, chemical coupling, and morphology of BFO- and RGO-supported BFO are established through X-ray diffraction, Raman and X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy studies. The modified band structure in RGO–BFO is obtained from the UV–vis spectroscopy study and supported by density functional theory (DFT). The photocatalytic degradation of Rhodamine B dye achieved under 120 min visible-light illumination is 94% by the RGO–BFO composite with a degradation rate of 1.86 × 10–2 min–1, which is 3.8 times faster than the BFO nanoparticles. The chemical oxygen demand (COD) study further confirmed the mineralization of an organic dye in presence of the RGO–BFO catalyst. The RGO–BFO composite shows excellent PEC performance toward water splitting, with a photocurrent density of 10.2 mA·cm–2, a solar-to-hydrogen conversion efficiency of 3.3%, and a hole injection efficiency of 98% at 1 V (vs Ag/AgCl). The enhanced catalytic activity of RGO–BFO is explained on the basis of the modified band structure and chemical coupling between BFO and RGO, leading to the fast charge transport through the interfacial layers, hindering the recombination of the photogenerated electron–hole pair and ensuring the availability of free charge carriers to assist the catalytic activity.

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