Sustainable Lignin‐Liquid Metal Photothermal Coating for Highly Efficient Solar Thermoelectric Generation

ABSTRACT Harvesting sunlight into electricity presents an attractive prospect. Solar thermoelectric generation (STEG) relying on complexity and compactness of optical absorbers and mechanical equipment is only applied in large‐scale power plants. Here, we develop a gradient nanostructured coating based on lignin and liquid metal (LM) that serves as a scalable and recyclable optical absorber. Density differences and surface coordination interactions are used to induce stable, gradient sedimentation of LM within the lignin matrix. This gradient nano‐structure exhibits synergetic mechanism of non‐radiative relaxation and localized surface plasmon resonance, leading to a high and broadband absorption of 96.0% from ultraviolet to near‐infrared region (250–2500 nm), surpassing most renewable and nonrenewable absorbers. Our lignin‐derived coating achieves hundreds kilograms‐scale production. A sequentially aligned stacking strategy is created for a meter‐scale flat‐panel STEG device, to offer a 64.7 V output voltage in outdoor conditions. Environmental and energy assessments further demonstrate that our lignin valorization mode achieves high green electricity productivity and establishes a carbon‐negative process, resulting in annual reduction of 489.63 kg CO ₂ equivalent per 1000 m ² . Our proposed “lignin‐liquid metal synergic photothermal enhancement” strategy represents a sustainable path in transforming industrial lignin into high‐performance and scalable energy conversion materials.