Chen Han

Carbon nitride is a scalable and low-cost organic semiconductor with promise for use in photoelectrochemical (PEC) devices, but its poor stability limits its practical use. This study establishes the importance of light intensity and applied electrochemical potential on the stability of cyanamide-functionalized carbon nitride photoanodes used for waste-derived alcohol oxidation. Operating under concentrated sunlight (3 suns) and low bias (0.4 V vs RHE) to irreversible morphological changes and self-oxidation, exacerbated by conductivity loss. These insights enabled the stabilization of carbon nitride photoelectrodes and paved the way for the development of a standalone PEC device with an integrated thermoelectric unit to convert heat into an additional internal bias-voltage, where carbon nitride efficiently drives alcohol oxidation coupled to CO₂-to-CO conversion for over 70 h. This work sets a benchmark for carbon nitride stability and PEC deployment, and highlights the need to revisit PEC testing protocols to unlock the full potential of emerging semiconductors.

The sustainable construction of multiple C–N bonds remains a fundamental challenge, particularly for complex carbon–nitrogen molecules that require multielectron and multistep processes. Hexamethylenetetramine (HMTA) is an essential chemical feedstock, while its conventional synthesis is energy and carbon-emission intensive. Recent studies indicate the promise of Cu-based catalysts for electrochemical HMTA formation, yet a single Cu site is inherently limited in coordinating the multiple hydrogenation and condensation steps necessary for simultaneously forming the two key HMTA precursors (i.e., (CH₂NH)₃ and N(CH₂OH)₃). Herein, we report a sustainable photoelectrocatalytic (PEC) approach for HMTA synthesis via coupling NO₃^– and HCHO using a Si-based photocathode integrated with hierarchical Cu/Co nanoarray cocatalysts (Cu/Co–Si). This architecture decouples light absorption and catalytic reaction, delivering a high HMTA faradaic efficiency of 80.62% at 0.2 V_RHE, over 3.2 times that of Cu–Si, and a yield rate of 5.43 μmol h^–1 cm^–2. Importantly, *NH₂OH generated on Co sites during NO₃^– reduction is identified as a key intermediate that couples directly with *HCHO to form an oxime (*CH₂═NOH), accelerating the formation of (CH₂NH)₃. Meanwhile, Cu sites favor the NH₃–HCHO condensation pathway to generate N(CH₂OH)₃. The rational dual-site strategy and photovoltaic compatibility offer a scalable, sustainable platform for solar-driven C–N coupling toward high-value chemicals.

Converting solar energy into chemicals and fuels through photoelectrocatalytic (PEC) process is challenging but holds significant potential for advancing sustainable development. Here we introduce an innovative system to realize solar-driven NH₃ production from waste nitrate by nano-structured top layer (NSTL) hybrid catalysts modified commercial Si absorber, to bridge the gap from fundamental understanding to the process engineering. Specifically, we employ a rationally designed Si/Cu-NSTL/Co(OH)₂ ternary photocathode featuring a Schottky barrier contact enabling optimized photo-carrier transport pathways and a beneficial co-adsorption configuration of *NO₃–H₂O moieties. This photocathode exhibits the best-known performance in the literature for the PEC conversion of NO₃ to NH₃, boasting an onset potential of approximately 1 V_RHE and a remarkable faradaic efficiency of nearly 100%. Building upon these findings, we develop the first large-scale unbiased PEC device (an artificial leaf) capable of simultaneously producing NH₃ and valorizing biomass, achieving a solar utilization efficiency of approximately 4%. Its scalability and practical feasibility have been further validated through rigorous outdoor testing with an assembled tandem device array. The process techno-economic assessment shows compelling economic viability of this technology across diverse application scenarios in NH₃ production, resulting in substantial savings of fossil fuel and a reduction of CO₂ emissions. We anticipate that this work will serve as a valuable resource for the design of next-generation photoelectrodes and devices, bringing us one step closer to realizing standalone solar-to-sustainable chemical applications.

Oxide‐derived Cu catalysts from Cu₂O microcrystals are capable of electrochemically converting CO₂ into various value‐added chemicals. However, their structural transformation and associated preferred products remain unclear, requiring further investigation. Herein, Cu₂O microcrystals with controllable low‐ and high‐index facets exposure are fabricated to differentiate the effects of initial exposed facets on their structural reconstruction and product selectivity in electrochemical CO₂ reduction reaction. Combined in situ characterizations and theoretical investigation reveal the direct correlations of Cu₂O reconstruction and product selectivity to its initial facet exposure. The Cu₂O low‐index facet, being more stable with a high energy barrier on material reduction, tends to partially maintain its original crystalline structure and larger Cu₂O particle size throughout the transformation. The derived flatter surface and limited Cu₂O/Cu interfaces result in a favorable selectivity toward 2‐electron transfer products. The chemically active Cu₂O high‐index facet (311) is energetically favorable to be reduced owing to the feasible protonation process, thus experiencing a drastic reconstruction with rich newly formed Cu nanoparticles and evolved fine Cu₂O grains; Such a reconstruction creates uncoordinated Cu species and abundant boundaries, benefiting charge transfer and increasing the local pH by confining OH⁻, thus leading to a high selectivity toward C₂₊ products.