environment each year, an emblem of our increasingly unsustainable economic system in which materials and energy are produced, used and promptly discarded. Photoreforming is a sunlight-driven technology that can help disrupt this linear model by simultaneously reclaiming the value in waste and contributing to renewable hydrogen production. This Review examines the advantages and challenges of photoreforming of real waste streams. By reviewing literature on photoreforming and conducting basic techno-economic and life cycle assessments, we identify key pathways for enhancing the impact of photoreforming for a carbon-neutral future.

The production of clean fuels and chemicals from waste feedstocks is an appealing approach towards creating a circular economy. However, waste photoreforming commonly employs particulate photocatalysts, which display low product yields, selectivity, and reusability. Here, a perovskite-based photoelectrochemical (PEC) device is reported, which produces H 2 fuel and simultaneously reforms waste substrates. A novel Cu 30 Pd 70 oxidation catalyst is integrated in the PEC device to generate value-added products using simulated solar light, achieving 60-90% product selectivity and ≈70-130 µmol cm −2 h −1 product formation rates, which corresponds to 10 2 -10 4 times higher activity than conventional photoreforming systems. The single-light absorber device offers versatility in terms of substrate scope, sustaining unassisted photocurrents of 4-9 mA cm −2 for plastic, biomass, and glycerol conversion, in either a two-compartment or integrated "artificial leaf " configuration. These configurations enable an effective reforming of non-transparent waste streams and facile device retrieval from the reaction mixture. Accordingly, the presented PEC platform provides a proof-ofconcept alternative towards photoreforming, approaching more closely the performance and versatility required for commercially viable waste utilization.

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The chemical inertness of polyethylene makes chemical recycling challenging and motivates the development of new catalytic innovations to mitigate polymer waste. Current chemical recycling methods yield a complex mixture of liquid products, which is challenging to utilize in subsequent processes. Here, we present an oxidative depolymerization step utilizing diluted nitric acid to convert polyethylene into organic acids (40% organic acid yield), which can be coupled to a photo- or electrocatalytic decarboxylation reaction to produce hydrocarbons (individual hydrocarbon yields of 3 and 20%, respectively) with H 2 and CO 2 as gaseous byproducts. The integrated tandem process allows for the direct conversion of polyethylene into gaseous hydrocarbon products with an overall hydrocarbon yield of 1.0% for the oxidative/photocatalytic route and 7.6% for the oxidative/electrolytic route. The product selectivity is tunable with photocatalysis using TiO 2 or carbon nitride, yielding alkanes (ethane and propane), whereas electrocatalysis on carbon electrodes produces alkenes (ethylene and propylene). This two-step recycling process of plastics can use sunlight or renewable electricity to convert polyethylene into valuable, easily separable, gaseous platform chemicals.

Solar-driven reforming uses sunlight and a photocatalyst to generate H 2 fuel from waste at ambient temperature and pressure. However, it faces practical scaling challenges such as photocatalyst dispersion and recyclability, competing light absorption by the waste solution, slow reaction rates and low conversion yields. Here, the immobilisation of a noble-metalfree carbon nitride/nickel phosphide (CN x j Ni 2 P) photocatalyst on textured glass is shown to overcome several of these limitations. The 1 cm 2 CN x j Ni 2 P panels photoreform plastic, biomass, food and mixed waste into H 2 and organic molecules with rates comparable to those of photocatalyst slurries. Furthermore, the panels enable facile photocatalyst recycling and novel photoreactor configurations that prevent parasitic light absorption, thereby promoting H 2 production from turbid waste solutions. Scalability is further verified by preparing 25 cm 2 CN x j Ni 2 P panels for use in a custom-designed flow reactor to generate up to 21 μmol H 2 m À 2 h À 1 under "real-world" (seawater, low sunlight) conditions. The application of inexpensive and readily scalable CN x j Ni 2 P panels to photoreforming of a variety of real waste streams provides a crucial step towards the practical deployment of this technology.