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Using an inexpensive and eco-friendly wood substrate, herein, a one-step calcination method is developed to deposit Co-Ni binary nanoparticles into aligned wood channels and an effective carbonized wood (CW) electrode (termed as Co/Ni-CW) is fabricated. Well distributed Co-Ni nanoparticles are achieved by the coordination bonds between the hydroxyl groups on wood matrix and soaked metal cations. Subsequently, high-temperature calcination promotes the nucleation of Co-Ni nanoparticles and the formation of CW. With the uniform distribution of Co-Ni nanoparticles and porous wood structure, not only is a high active surface area, but also the electron and mass diffusion pathways are enhanced. Thus, the as-prepared Co/Ni-CW affords the current density of 10 mA cm -2 at low overpotentials of 330 and 157 mV for oxygen and hydrogen evolution, respectively. Remarkably, when the wood-based bifunctional electrocatalyst is used as both the anode and cathode, a low cell voltage of 1.64 V is required to reach the current density of 10 mA cm -2 . Compared with most substrates used in bifunctional electrocatalysts, the abundance, low cost, eco-friendliness, and easy operation of woodbased catalysts allow for an active and scalable electrode for water splitting and many other energy storage devices.

The architecture of cellulose nanomaterials is definitized by random deposition and cannot change in response to shifting application requirements. Herein, we present a magnetic field-controlled cellulose film derived from wood that exhibits great magnetic properties and reliable tunability enabled by incorporated Fe3O4 nanoparticles and cellulose nanofibers (CNF) with a large length-diameter ratio. Fe3O4 nanoparticles are dispersed in suspensions of CNF so as to enhance the magnetic response. The plane magnetic CNF can be processed to form a three-dimensional (3D) flower-like structure along the magnetic induction line after applying an external magnet. Inspired by the fluidic transport in natural flowers, a bilayer structure was created using the 3D flower-like film as the solar energy receiver and natural wood as the water pathway in a solar-derived evaporation system. Compared with a planar cellulose film decorated with Fe3O4, the 3D structure design can greatly improve the evaporation rate from 1.19 to 1.39 kg m–2 h–1 and the efficiency from 76.9 to 90.6% under 1 sun. Finite element molding further reveals that the 3D structural top layer is beneficial for the formation of a gradient temperature profile and the improvement of the energy efficiency through the reduction of thermal radiation. The magnetically controlled fabrication represents a promising strategy for designing cellulose nanomaterials with a complicated structure and controllable topography, which has a wide spectrum of applications in energy storage devices and water treatment.