The need for cleaner alternative energy to fossil fuels has led to the development of a new realm of highly–efficient photoactive 2D nanostructures. With a thickness of a single or few atomic layers, the 2D nanomaterials (NMs) have high surface area. The strong in-plane chemical bonds along with weak van der Waals interaction make these materials lucrative for surface related applications. Photocatalytic water splitting technique is a promising alternative to produce hydrogen using facile and cost effective methods. In the current review, recent progress made in photocatalytic hydrogen evolution reaction (HER) using 2D nanomaterials and composite heterostructures is described. State of the art protocols designed for the synthesis of 2D NMs is discussed in detail. The review illustrates the DFT based studies against the new set of 2D NMs, which also highlights the importance of structural defects and doping in the electronic structure. Additionally, the review describes the influence of electronic, structural and surface manipulation strategies. These impact the electronic structures, intrinsic conductivity and finally the output towards HER. Moreover, this review also provides a fresh perspective on the prospects and challenges existing behind the application and fabrication strategies.

Ni and NiSn supported on zirconia (ZrO₂) and on indium (In)-incorporated zirconia (InZrO₂) catalysts were prepared by a wet chemical reduction route and tested for hydrogenation of CO₂ to methanol in a fixed-bed isothermal flow reactor at 250 °C. The mono-metallic Ni (5%Ni/ZrO₂) catalysts showed a very high selectivity for methane (99%) during CO₂ hydrogenation. Introduction of Sn to this material with the following formulation 5Ni5Sn/ZrO₂ (5% Ni-5% Sn/ZrO₂) showed the rate of methanol formation to be 0.0417 μmol/(g_cat·s) with 54% selectivity. Furthermore, the combination NiSn supported on InZrO₂ (5Ni5Sn/10InZrO₂) exhibited a rate of methanol formation 10 times higher than that on 5Ni/ZrO₂ (0.1043 μmol/(g_cat·s)) with 99% selectivity for methanol. All of these catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy, CO₂-temperature-programmed desorption, and density functional theory (DFT) studies. Addition of Sn to Ni catalysts resulted in the formation of a NiSn alloy. The NiSn alloy particle size was kept in the range of 10–15 nm, which was evidenced by HRTEM study. DFT analysis was carried out to identify the surface composition as well as the structural location of each element on the surface in three compositions investigated, namely, Ni₂₈Sn₂₇, Ni₁₈Sn₃₇, and Ni₃₇Sn₁₈ bimetallic nanoclusters, and results were in agreement with the STEM and electron energy-loss spectroscopy results. Also, the introduction of “Sn” and “In” helped improve the reducibility of Ni oxide and the basic strength of catalysts. Considerable details of the catalytic and structural properties of the Ni, NiSn, and NiSnIn catalyst systems were elucidated. These observations were decisive for achieving a highly efficient formation rate of methanol via CO₂ by the H₂ reduction process with high methanol selectivity.