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

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.