▎ 摘　　要

Developing cost-effective electrocatalysts for proton electrolyte membrane fuel cell electrodes has proven challenging because of the difficulty in finding inexpensive alternatives to platinum that are as catalytically active. A more straightforward approach is to minimize the cost of using platinum by reducing its mass while preserving its active area, that is, by reducing the nanoparticle diameter. However, smaller nanoparticles are especially vulnerable to loss via dissolution and ripening. Here, we combat this degradation by preparing a hybrid graphene-nanocellulose sandwich to securely encapsulate platinum catalysts in a robust and conductive envelope. This securely anchors the nanoparticles, preventing the loss of active area through ripening or detachment. Our nanocellulose hybrid was prepared via the facile and scalable carbonization of a bacterial cellulose feedstock, yielding a high-surface-area, robust, and conductive catalyst support. Cyclic voltammetry and transmission electron microscopy reveal that the graphene-nanocellulose composite significantly reduces the effective surface area losses of ultrafine (<3 nm diameter) nanoparticle catalysts, primarily by preventing Ostwald ripening and dissolution.