Construction of a 2D lamellar membrane for a combination of photocatalytic hydrogen evolution and photothermal water evaporation

Solar energy can help solve the energy and water shortage crisis. Developing a single material that can exhibit both photocatalytic hydrogen evolution (PHE) and photothermal water evaporation (PWE) represents a new concept to simultaneously realize green energy and fresh water supply. In this study, a series of 2D lamellar membranes (2DLMs) based on a conventional semiconductor BiOCl nanosheet was designed as an ensemble, and its combined application for PHE and PWE was explored, in which cellulose nanofibers (CNFs), carbon nanotubes (CNTs), and a self-assembly of CNF@CNT were also used. The PHE and PWE efficiencies are closely related to the conversion of solar energy and the state of the water molecules. Owing to the high light-to-thermal conversion, enhanced water transfer, and the low evaporation enthalpy of confined water, a composite made of BiOCl and CNF@CNT 2DLM (BOC-CNF@CNT) could rapidly reach a surface temperature of 46.6 °C, with its PWE rate reaching up to 2.05 kg·m−2·h−1. Moreover, owing to the high photogenerated carrier transport, strong photothermal effect, and the action of confined water, the PHE rate of BOC-CNF@CNT is 1.99-fold that of the composite made of BiOCl and CNF 2DLM (BOC-CNF) and 1.42-fold that of the composite made of BiOCl and CNT 2DLM (BOC-CNT). This work provides a new and effective strategy for a comprehensive utilization of solar energy to simultaneously produce clean hydrogen and fresh water.