Periodic Reporting for period 5 - ReSuNiCo (Inverted Reactive Spray Processes for Sulphide/Nitride High Surface Area Electrode Coatings)
Reporting period: 2025-01-01 to 2025-06-30
The ReSuNiCo Advance ERC project developed the first scalable flame spray pyrolysis (FSP) method for synthesizing complex metal sulfide nanoparticles, merging combustion science with industrial nanomanufacturing. Metal sulfides, especially binary and ternary types, are promising for photocatalysis, energy storage, and electronics, but traditional wet-chemical and solid-state syntheses lack throughput and fine control. FSP offers continuous production but previously faced issues with precursor volatility, sulfidation control, and combustion dynamics. The first work packages of the project (WP1–WP2) focused on developing a single-droplet combustion reactor to screen metal–organic precursors under controlled conditions. Using sulfur-rich solvents like tetrahydrothiophene (THT), copper naphthenate–THT was identified as a model system. It revealed a two-step process: THT ignition formed a sulfur-rich zone, followed by micro-explosions releasing metal–sulfur fragments that completed sulfidation. Low-volatility precursors enabled synchronized metal release and uniform particles, unlike high-volatility ones, which showed staggered release due to flame turbulence. Advanced diagnostics (hyperspectral and filtered emission imaging) mapped flame morphology and confirmed micro-explosions as a general release mechanism. WP3 developed a validated 1D droplet combustion model incorporating heat/mass transfer and reaction kinetics, predicting evaporation, shell formation, and rupture, which guided precursor and reactor design. WP4 applied these insights to build a sulfur-optimized FSP reactor, producing gram-scale binary (MnS, Cu1.8S ZnS, In2S₃, Ag2S, SnS, CoS, Bi2S3), ternary (CuInS2, AgBiS2, AgInS2, CoIn2S4, ZnIn2S4 and MnIn2S4), and hybrid (Pt–Cu1.8S Cu1.8S–ZnS) with controllable phases. The Sn-doped In2S₃ with a narrowed bandgap improved photocurrent and solar-to-hydrogen efficiency. WP5 disseminated findings via publications and patents. Exploratory experiments demonstrated the feasibility of extending the method to nitrides and oxynitrides using NH₃ gas. Overall, this project establishes a scalable, general platform for flame-based synthesis of functional single- and multi-metal sulfide nanoparticles.
The project began with the selection of metal–organic precursors and sulfur-rich solvents to achieve controlled and efficient sulfidation. This was followed by detailed single-droplet combustion screening (WP1 and WP2), where advanced real-time diagnostics, including flame emission spectroscopy and hyperspectral & filtered emission imaging (HIS-FEI) were employed for droplet combustion dynamics and metal release. These findings enabled the development of a robust mathematical combustion model (WP3) that precisely simulated droplet behavior, evaporation, shell formation, and rupture sequences. Building on these foundations, a flame spray pyrolysis reactor was designed to produce first comprehensive library of binary metal sulfides in 2023, which was later expanded to include doped and noble metal-functionalized sulfide nanoparticles (WP4). The project’s achievements were disseminated through over 12 high-impact publications and secured 2 patents (WP5), as detailed below:
Balakrishnan et al., Project Repository J. 2020, 6, 90-93; Li et al., Combustion and Flame, 2020, 215(5), 389-400; Stodt et al., Combustion and Flame, 2022, 240, 112043; Pokhrel et al., Adv. Mater. 2023, 35(28), 2211104; Groneveld et al., Nanoscale Horizon, 2024, 9(6), 875-1054; Pokhrel et al., Powder Technol. 2025, 465, 121318: All these Publications identified exothermic precursor–solvent systems enabling multiple μ-explosions, demonstrated droplet combustion for advanced sulfide synthesis, used FES for real-time combustion mapping, and achieved homogeneous nanoparticle formation via simultaneous metal release.
Balakrishnan et al., Project Repository J. 2020, 6, 90-93; Pokhrel et al., Adv. Mater. 2023, 35(28), 2211104; Pokhrel et al., Adv. Func. Mater. 2024, 2411521; Pokhrel et al., Powder Technol. 2025, 465, 121318; Martuza et al., Small, 2025, 2409993: These high-impact publications demonstrate the successful implementation of the flame spray reactor, developed based on insights gained from single droplet screening. The metal sulfide classes span a broad spectrum, including binary, mixed binary, ternary, and noble metal-functionalized metal sulfides.
Pokhrel et al.; Energy & Fuels, 2020, 34(11), 13209–1322; Balakrishnan et al., Chem.-A Eur. J. 2021, 27, 6390-6406; Pokhrel et al., KONA Powder Part. J., 2025, 42, 170-187; Martuza et al., L. Mädler, S. Pokhrel, Adv. Energy Sust. Res. 2025, 2400448: These review articles highlight the crucial roles of oxides and sulfides in batteries, solar cells, and catalytic applications.
S. Pokhrel, J. Stahl, L. Mädler, Method for preparing a metal sulfide material and metal sulfide material obtainable thereby, German patent, U10441DE, 102022126378.9 October 12, 2022; (2) S. Pokhrel, M. Al. Martuza, L. Mädler, Flame synthesis of Ternary Metal Sulfides of the type ABS2 (A = Ag, Cu and B = In, Bi) and AB2S4 (A = Mn, Co, Zn and B = In), German patent submitted to University of Bremen InnoWi, April, 2025: These patents demonstrate, for the first time, the successful synthesis of ternary metal sulfides directly from flame processes.
Balakrishnan et al., Project Repository J. 2020, 6, 90-93; Li et al., Combustion and Flame, 2020, 215(5), 389-400; Stodt et al., Combustion and Flame, 2022, 240, 112043; Pokhrel et al., Adv. Mater. 2023, 35(28), 2211104; Groneveld et al., Nanoscale Horizon, 2024, 9(6), 875-1054; Pokhrel et al., Powder Technol. 2025, 465, 121318: All these Publications identified exothermic precursor–solvent systems enabling multiple μ-explosions, demonstrated droplet combustion for advanced sulfide synthesis, used FES for real-time combustion mapping, and achieved homogeneous nanoparticle formation via simultaneous metal release.
Balakrishnan et al., Project Repository J. 2020, 6, 90-93; Pokhrel et al., Adv. Mater. 2023, 35(28), 2211104; Pokhrel et al., Adv. Func. Mater. 2024, 2411521; Pokhrel et al., Powder Technol. 2025, 465, 121318; Martuza et al., Small, 2025, 2409993: These high-impact publications demonstrate the successful implementation of the flame spray reactor, developed based on insights gained from single droplet screening. The metal sulfide classes span a broad spectrum, including binary, mixed binary, ternary, and noble metal-functionalized metal sulfides.
Pokhrel et al.; Energy & Fuels, 2020, 34(11), 13209–1322; Balakrishnan et al., Chem.-A Eur. J. 2021, 27, 6390-6406; Pokhrel et al., KONA Powder Part. J., 2025, 42, 170-187; Martuza et al., L. Mädler, S. Pokhrel, Adv. Energy Sust. Res. 2025, 2400448: These review articles highlight the crucial roles of oxides and sulfides in batteries, solar cells, and catalytic applications.
S. Pokhrel, J. Stahl, L. Mädler, Method for preparing a metal sulfide material and metal sulfide material obtainable thereby, German patent, U10441DE, 102022126378.9 October 12, 2022; (2) S. Pokhrel, M. Al. Martuza, L. Mädler, Flame synthesis of Ternary Metal Sulfides of the type ABS2 (A = Ag, Cu and B = In, Bi) and AB2S4 (A = Mn, Co, Zn and B = In), German patent submitted to University of Bremen InnoWi, April, 2025: These patents demonstrate, for the first time, the successful synthesis of ternary metal sulfides directly from flame processes.
This project has unlocked the first truly scalable and controllable route to complex metal sulfide nanoparticles via flame spray pyrolysis (FSP), a leap beyond the limits of wet-chemical and solid-state synthesis, which cannot combine throughput, precision, and compositional flexibility. Until now, FSP was hindered by poor control over precursor volatility, incomplete sulfidation, and chaotic droplet combustion. We have bridged these gaps by merging single-droplet combustion diagnostics with advanced modelling, directly linking combustion microphysics to nanostructure formation. We discovered and quantified a universal two-stage “micro-explosion” pathway for metal–sulfur release, using custom hyperspectral/filtered emission imaging to resolve flame morphology, droplet shrinkage, and precursor fragmentation in real time. Our 1D quasi-steady droplet combustion model now predicts evaporation, shell rupture, and reaction sequences, enabling rational design of precursor chemistry and reactor conditions. These insights led to a sulfur-optimized FSP reactor that produces gram-scale binary, ternary, and hybrid sulfides with tunable phase, doping, and heterostructures, including bandgap-engineered systems achieving record photocurrent and ABPE values. Early results show the platform’s versatility for nitrides, oxynitrides, and other non-oxides via ammonia-assisted conversion. While the project has come to an end, we deliver:
• Flame-based synthesis platform for binary/ternary metal sulfides,
• Extensive application-ready metal sulfide libraries for photocatalysis, energy conversion, and electronics;
• Integrated experimental and computational framework enabling industrial-scale design,
• Prototype devices outperforming the state-of the art synthesis and demonstrating step-change performance from tailored nanostructures.
This work will redefine the state of the art in nanoparticle manufacturing, setting the foundation for on-demand, continuous, and sustainable production of non-oxide high-value functional materials.
• Flame-based synthesis platform for binary/ternary metal sulfides,
• Extensive application-ready metal sulfide libraries for photocatalysis, energy conversion, and electronics;
• Integrated experimental and computational framework enabling industrial-scale design,
• Prototype devices outperforming the state-of the art synthesis and demonstrating step-change performance from tailored nanostructures.
This work will redefine the state of the art in nanoparticle manufacturing, setting the foundation for on-demand, continuous, and sustainable production of non-oxide high-value functional materials.