Pt single-atom materials possess an ideal atom economy but suffer from limited intrinsic activity and side reaction of producing H2O2 in catalyzing the oxygen reduction reaction (ORR); platinum alloys have higher intrinsic activity but weak stability. Here, we demonstrate that anchoring platinum alloys on single-atom Pt-decorated carbon (Pt-SAC) surmounts their inherent deficiencies, thereby enabling a complete four-electron ORR pathway catalysis with high efficiency and durability. Pt3Co@Pt-SAC demonstrates an exceptional mass and specific activities 1 order of magnitude higher than those of commercial Pt/C. They are durable throughout 50000 cycles, showing only a 10 mV decay in half-wave potential. An in situ Raman analysis and theoretical calculations reveal that Pt3Co core nanocrystals modulate electron structures of the adjacent Pt single atoms to facilitate the intermediate absorption for fast kinetics. The superior durability is attributed to the shielding effect of the Pt-SAC coating, which significantly mitigates the dissolution of Pt3Co cores. The hybridizing strategy might promote the development of highly active and durable ORR catalysts.

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Often the choice of semiconductor material for light‐chemical energy conversion in solar cell technology is TiO2 polymorphs. However, quantum‐mechanical phenomena of electron self‐trapping (polaron) in these polar semiconductors present a challenge to optimize their performance for absorption of solar radiation. The electron trapped in the defect site of the lattice may suppress the recombination of charge carriers and improve the efficiency of light‐chemical energy conversion. Therefore, it is crucial to study polarons in transition metal oxides and semiconductors using first‐principles methods to elucidate the nature of charge carriers and trapping sites for ameliorating the performance of energy conversion. In this work, a comprehensive review is presented using selected literature of polaron studies in TiO2 from first‐principles methods. Overview of the Landau–Pekar model to the recent development of ab initio theory of polaron is presented. The popular DFT+U approach and hybrid functional method are discussed to show the general way of studying polaron using ab initio methods. Introduction of electron‐phonon interaction and the ab initio theory of polaron are briefly presented Therefore, this review presents the development of first‐principles methods from Landau theory to the state‐of‐the‐art to study polarons using TiO2 as the toy model. Finally, conclusions and future perspectives are outlined.

Upgrading of biomass wastes to value-added materials has been incessantly pursued worldwide with diverse applications, especially deploying photocatalytic composites encompassing metal oxides with acidic and carbon compounds. Herein, the fabrication of a morphologically unique acidic catalyst encompassing a two-dimensional (2D) TiO2/g-C3N4 heterojunction feature is described for the generation of 5-hydroxymethylfurfural (5-HMF), which exploits the acidic/ionic liquid (IL) bifunctional photocatalysis under visible light. The structural integrity of the synthesized TiO2/g-C3N4/SO3H­(IL) was corroborated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy–energy-dispersive spectroscopy (EDX–EDS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), UV–vis, Tauc plots, transmission electron microscopy (TEM), and Brunauer–Emmett–Teller–Barrett–Joyner–Halenda (BET–BJH) analyses. Keeping environmental impact in mind, there are compelling advantages in the development of bio-derived pathways to access ILs from natural renewable resources. The outcomes of environmental assessments have revealed that the incorporation of TiO2 in g-C3N4 and ClSO3H can reduce the probability of recombination due to ionic charges present, therefore enhancing the photocatalytic activity via the transformation of cellulose and glucose to produce 5-HMF in higher yields, with the optimum conditions being reaction in water under a blue light-emitting diode (LED), at 100 °C, for 1–1.5 h. The main advantages of this production method include minimum number of synthetic steps as well as ample availability of and easy access to primary ingredients. While a significant volume of 5-HMF was produced under blue light-emitting diode (LED) radiation, the selectivity was drastically reduced in the dark. The salient attributes of the catalyst comprise stability in air, robustness, reusability, and its overall superior activity that is devoid of hazardous additives or agents. This inimitable method has uncovered a newer strategy for enhancing the photocatalytic attributes of deployed semiconducting materials for numerous photocatalytic functions while adhering to the tenets of environmental friendliness.

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