Platinum diselenide (PtSe2) has shown great potential as a candidate two‐dimensional (2D) material for broadband photodetectors and electrocatalysts because of its unique properties compared to conventional 2D transition metal dichalcogenides. Synthesis of 2D PtSe2 with controlled layer number is critical for engineering the electronic behavior to be semiconducting or semimetallic for targeted applications. Electrochemical exfoliation has been investigated as a promising approach for mass‐producing in a cost‐effective manner, but obtaining high‐quality films with control over electronic properties remains difficult. Here, we demonstrate wafer‐scale 2D PtSe2 films with pre‐determined electronic types based on a facile solution‐based strategy. Semiconducting or semimetallic PtSe2 nanosheets with large lateral sizes are produced via electrochemically driven molecular intercalation, followed by centrifugation‐based thickness sorting. Finally, gate‐tunable broadband visible and near‐infrared photodetector arrays are realized based on semiconducting PtSe2 nanosheet films, while semimetallic films are used to create catalytic electrodes for overall water splitting with long‐term stability.

Nanostructuring of Pt nanocatalysts increases the surface‐to‐volume ratio, thus enabling efficient usage of Pt for hydrogen evolution reaction (HER). Direct electrochemical reduction of Pt on the electrode can produce nanostructured Pt catalysts, which has been time‐consuming for the conventional colloidal synthesis. However, carbon‐based growth templates commonly used to create Pt nanoparticles offer limited control over morphologies and HER performance. Herein, a facile electrochemical synthesis of Pt nanoflowers (NFs) with well‐defined petals is presented. Semiconducting MoS2 nanosheets are solution processed into a film on a carbon paper (CP) to synthesize Pt NFs upon reduction of Pt precursor. The Pt NFs show higher HER activities than spherical or spiky Pt nanoparticles because of their larger active surface area and enable faster release of hydrogen bubbles during HER. By generating sulfur vacancies and MoOx on the MoS2 template using a reactive ion etching, the areal density and spatial uniformity of Pt NFs can be greatly enhanced and a mass activity can be achieved more than 10 times as high as that of the conventional Pt/C electrode. Multiple electrodes with nearly similar electrochemical properties can be repeatedly produced by using a single precursor solution, which highlights the cost‐efficiency and scalability of our synthesis strategy.

Platinum Nanocatalysts In article number http://doi.wiley.com/10.1002/smsc.202200043, Joohoon Kang and co‐workers demonstrate precisely controllable nanostructuring of platinum on various solution‐processed 2D nanomaterials in large scale. This approach allows mass production of platinum nanoflowers, which can maximize catalytic properties and operation stability.