As detailed in Table , control and exploitation of nanoscale morphology is currently a heavy focus of green hydrogen production catalysts. Several factors play into this research focus. First, it is desirable in electrocatalysis to maximize the electrochemically active surface area of the catalyst to increase the number of active sites available, and in photocatalysis, to maximize light absorption. In addition, the dispersal of precious metals onto a nanostructured surface can improve the catalytic properties on an atomic metals basis. Finally, in heterostructured semiconductor photocatalysts as well as Schottky junction materials, managing variables such as exciton separation, carrier diffusion, and mass transfer becomes quite complicated. The relative prevalence of the most common nanomaterial types in GHE research are shown in Table , normalized to the number of publications in each respective research area. For green hydrogen production, the "Nanoparticles" concept is the most common, followed by "Nanosheets" and "Nanocomposites". The popularity of nanoparticles is well known, with Pt nanoparticles being considered among the top-performing HER electrocatalysts. Concerning the almost equally popular nanosheets, materials chemistry has been enamored with this 2-dimensional materials for the last 15 years, and a diverse set of products can be convinced to form into atomically thin dimensions to give rise to novel and useful phenomena for catalysis. When combined with other materials (into nanocomposites), high surface area catalysts can be prepared which take advantage of nanoscale effects such as quantum confinement and surface plasmon resonance, as well as interfacial effects including the aforementioned semiconductor heterojunctions and Schottky junctions. In addition to the transition metal dichalcogenides (e.g. MoS2) and graphitic carbon nitride (C3N4) mentioned in Table , nanosheets used for green hydrogen production have thus far included layered double hydroxides, graphene, MXenes, bismuth oxyhalides, halide perovskites, and 2D MOFs 30 and covalent-organic frameworks. The vast selection of electronic materials available and the toolbox of synthetic methods impart control over particle size, shape, doping and defect levels, crystallinity, and material interfaces, thus motivating the large number of observed studies on nanoscale morphology in green hydrogen production.