Conformal Microfluidic‐Blow‐Spun 3D Photothermal Catalytic Spherical Evaporator for Omnidirectional Enhanced Solar Steam Generation and CO2 Reduction

Abstract Solar‐driven water evaporation and valuable fuel generation is an environmentally friendly and sustainable way for clean water and energy production. However, a few bottlenecks for practical applications are high‐cost, low productivity, and severe sunlight angle dependence. Herein, solar evaporation with enhanced photocatalytic capacity that is light direction insensitive and of efficiency breakthrough by virtue of a three‐dimensional (3D) photothermal catalytic spherical isotopic evaporator is demonstrated. A homogeneous layer of microfluidic blow spun polyamide nanofibers loaded with efficient light absorber of polypyrrole nanoparticles conformally wraps onto a lightweight, thermal insulating plastic sphere, featuring favorable interfacial solar heating and efficient water transportation. The 3D spherical geometry not only guarantees the omnidirectional solar absorbance by the light‐facing hemisphere, but also keeps the other hemisphere under shadow to harvest energy from the warmer environment. As a result, the light‐to‐vapor efficiency exceeds the theoretical limit, reaching 217% and 156% under 1 and 2 sun, respectively. Simultaneously, CO2 photoreduction with generated steam reveals a favorable clean fuels production rate using photocatalytic spherical evaporator by secondary growth of Cu2O nanoparticles. Finally, an outdoor demonstration manifests a high evaporation rate and easy‐to‐perform construction on‐site, providing a promising opportunity for efficient and decentralized water and clean fuel production.


g of FeCl
was dissolved in 150 g of DI water. The as-spun PA66 sphere was immersed in

Characterization
The morphology of the as-spun NFs was observed by scanning electron microscope (SEM) with a QUANTA 200 (Philips-FEI, HOLLAND) instrument at 200 kV. X-ray photoelectron spectroscopy (XPS) spectra were obtained on a thermo ESCALAB 250XI X-ray photoelectron spectrometer. Crystallographic information was obtained using X-ray diffraction (XRD, Bruker-AXS D8 ADVANCE X-ray diffractometer). Fourier transform infrared (FT-IR) spectra were recorded on a Nicolet 6700 FT-IR spectrometer. Contact angles were measured with a KRÜSS DSA100 (KRÜSS, Germany) contact-angle test system at ambient temperature. The transmittance and reflectance spectra of PA66/PPy spheres were obtained using a UV-visible spectrophotometer (Lambda 750 S UV Spectrometer). The infrared images were taken by a FLIR E8 infrared camera.

Evaluation of Solar Evaporation in Laboratory
The plastic container with a radius of 5 cm and a height of 6 cm was filled with simulated seawater (3.5 wt% NaCl solution). The PA66/PPy 0.001 , PA66/PPy 0.01 , PA66/PPy 0.05 PA66/PPy 0.1 and PA66/PPy 0.2 spherical evaporators were placed on the polystyrene (PS) foam with the tail contact with the bulk water, respectively. After stabilized for 20 min, a simulated sunlight (by 300 W xenon arc lamp) with a radiation intensity of 1 kW m -2 (1 sun) was used to drive steam generation at room temperature of 24 o C and humidity of 56%. The water mass change of a single spherical evaporator was monitored by an electrical balance and recorded every 10 min. and PA66/PPy/Cu 2 O films were conducted for CO and CH 4 evolution by placing the photocatalysts on the surface of water in the quartz reactor. The reactor was purged with CO 2 for ten minutes to exhaust the air mixtures and CO 2 was filled in the device. Gas samples were analyzed using gas chromatography every hour. The purity of CO 2 used in this experiment is 99.999%.

Water Evaporation Outdoors
A model house of dimensions 40 × 30 × 35 cm (length × width × height) was used to evaluate outdoor evaporation rate. placed on a platform scale was made to load solar evaporators, which was placed in a natural environment to test the evaporation rate of the evaporator. The

Calculation of photothermal conversion efficiency
The evaporation rate and light-to-vapor efficiency of water can be calculated by (1)  is the energy required for the evaporation system to heat from the initial temperature T 1 to the final temperature T 2 . P in is the light intensity on the evaporator.
According to the reported method, we measured the water vaporization enthalpy of PA66/PPy compoiste. The bulk water and PA66/PPy evaporator with the same surface area were placed in a closed space. The experiment was carried out in dark conditions under ambient pressure at room temperature. The mass change is recorded every hour and shown in Table S1.
Where E PA66/PPy is the equivalent vaporization enthalpy of water in PA66/PPy and m PA66/PPy is the solar evaporation rate of PA66/PPy.