Bias-Free Solar Upcycling of Nitrate and Glycerol with Highly Efficient and Durable Organic Semiconductor-Based Photoelectrodes.

Abstract

The sustainable management of biodiesel byproducts, nitrate (NO₃ ^-) and glycerol, remains a critical environmental challenge, disrupting global nitrogen and carbon cycles. Addressing this issue from a materials science perspective, a bias-free photoelectrochemical (PEC) upcycling system based on the integration of functional energy materials is presented. A nickel-iron-phosphorus (Ni-Fe-P) electrocatalyst exhibits synergistic bi-functional activity for selective NO₃ ^- reduction and glycerol oxidation, driven by the redox dynamics of Ni and Fe and electronic modulation by phosphorus incorporation. Through a metal-foil encapsulation strategy, the catalyst is integrated with organic semiconductor (OS)-based photoanodes and photocathodes, forming a highly efficient OS-based PEC system capable of stable operation under continuous solar illumination. The individual photoelectrodes demonstrate photocurrent densities of +15.7 and-14.8 mA cm^-2 under AM 1.5G conditions, while exhibiting remarkable stability with over 96% of initial performance retained after 60 h. To enable bias-free solar upcycling, a dual-photoelectrode PEC configuration is constructed, delivering a high reaction current of 11.04 mA cm^-2 along with >95% Faradaic efficiencies and excellent selectivity for both ammonia (NH₃) and formic acid (FA) production. This work underscores the potential of materials-driven PEC platforms for selective solar chemical upcycling.