Closed-Loop Multi-Objective Optimization for Cu-Sb-S Photo-Electrocatalytic Materials' Discovery.

Copper antimony sulfides are regarded as promising catalysts for photo-electrochemical water splitting because of their earth abundance and broad light absorption. The unique photoactivity of copper antimony sulfides is dependent on their various crystalline structures and atomic compositions. Here, a closed-loop workflow is built, which explores Cu-Sb-S compositional space to optimize its photo-electrocatalytic hydrogen evolution from water, by integrating a high-throughput robotic platform, characterization techniques, and machine learning (ML) optimization workflow. The multi-objective optimization model discovers optimum experimental conditions after only nine cycles of integrated experiments-machine learning loop. Photocurrent testing at 0 V versus reversible hydrogen electrode (RHE) confirms the expected correlation between the materials' properties and photocurrent. An optimum photocurrent of -186 µA cm-2 is observed on Cu-Sb-S in the ratio of 9:45:46 in the form of single-layer coating on F-doped SnO2 (FTO) glass with a corresponding bandgap of 1.85 eV and 63.2% Cu1+ /Cu species content. The targeted intelligent search reveals a nonobvious CuSbS composition that exhibits 2.3 times greater activity than baseline results from random sampling.

Machine learning-assisted optimization of multi-metal hydroxide electrocatalysts for overall water splitting.

Green hydrogen produced via electrochemical water splitting is a suitable candidate to replace emission-intensive fuels. However, the successful widespread adoption of green hydrogen is contingent on the development of low-cost, earth-abundant catalysts. Herein, machine learning models built on experimental data were used to optimize the precursor ratios of hydroxide-based electrocatalysts, with the objective of improving the product's electrocatalytic performance for overall water splitting. The Neural Network-based models were found to be the most effective in predicting and minimizing the overpotentials of the catalysts, reaching a minimum in two iterations. The relatively mild reaction conditions of the synthesis procedure, coupled with its scalability demonstrated herein, renders the optimized catalyst relevant for industrial implementation in the future. The optimized catalyst, characterized to be a molybdate-intercalated CoFe LDH, demonstrated overpotentials of 266 and 272 mV at 10 mA cm-2 for oxygen and hydrogen evolution reactions respectively in alkaline electrolyte, alongside unwavering stability for overall water splitting over 50 h. Overall, our results reflect the efficacy and advantages of machine learning strategies to alleviate the time and labour-intensive nature of experimental optimizations, which can greatly accelerate electrocatalysts research.

Surface charge as activity descriptors for electrochemical CO2 reduction to multi-carbon products on organic-functionalised Cu.

Intensive research in electrochemical CO2 reduction reaction has resulted in the discovery of numerous high-performance catalysts selective to multi-carbon products, with most of these catalysts still being purely transition metal based. Herein, we present high and stable multi-carbon products selectivity of up to 76.6% across a wide potential range of 1 V on histidine-functionalised Cu. In-situ Raman and density functional theory calculations revealed alternative reaction pathways that involve direct interactions between adsorbed histidine and CO2 reduction intermediates at more cathodic potentials. Strikingly, we found that the yield of multi-carbon products is closely correlated to the surface charge on the catalyst surface, quantified by a pulsed voltammetry-based technique which proved reliable even at very cathodic potentials. We ascribe the surface charge to the population density of adsorbed species on the catalyst surface, which may be exploited as a powerful tool to explain CO2 reduction activity and as a proxy for future catalyst discovery, including organic-inorganic hybrids.

In Situ Formed Magnesiophilic Sites Guiding Uniform Deposition for Stable Magnesium Metal Anodes.

Owing to its high volumetric capacity and natural abundance, magnesium (Mg) metal has attracted tremendous attention as an ideal anode material for rechargeable Mg batteries. Despite Mg deposition playing an integral role in determining the cycling lifespan, its exact behavior is not clearly understood yet. Herein, for the first time, we introduce a facile approach to build magnesiophilic In/MgIn sites in situ on a Mg metal surface using InCl3 electrolyte additive for rechargeable Mg batteries. These magnesiophilic sites can regulate Mg deposition behaviors by homogenizing the distributions of Mg-ion flux and electric field at the electrode-electrolyte interphase, allowing flat and compact Mg deposition to inhibit short-circuiting. The as-designed Mg metal batteries achieve a stable cycling lifespan of 340 h at 1.0 mA cm-2 and 1.0 mAh cm-2 using Celgard separators, while the full cell coupled with Mo6S8 cathode maintains a high capacity retention of 95.5% over 800 cycles at 1 C.

High Utilization of Composite Magnesium Metal Anodes Enabled by a Magnesiophilic Coating.

Metallic magnesium is a promising high-capacity anode material for energy storage technologies beyond lithium-ion batteries. However, most reported Mg metal anodes are only cyclable under shallow cycling (≤1 mAh cm-2) and thus poor Mg utilization (<3%) conditions, significantly compromising their energy-dense characteristic. Herein, composite Mg metal anodes with high capacity utilization of 75% are achieved by coating magnesiophilic gold nanoparticles on copper foils for the first time. Benefiting from homogeneous ionic flux and uniform deposition morphology, the Mg-plated Au-Cu electrode exhibits high average Coulombic efficiency of 99.16% over 170 h cycling at 75% Mg utilization. Moreover, the full cell based on Mg-plated Au-Cu anode and Mo6S8 cathode achieves superior capacity retention of 80% after 300 cycles at a low negative/positive ratio of 1.33. This work provides a simple yet effective general strategy to enhance Mg utilization and reversibility, which can be extended to other metal anodes as well.

Sulfurized Cyclopentadienyl Nanocomposites for Shuttle-Free Room-Temperature Sodium-Sulfur Batteries.

A major challenge hindering the practical adoption of room-temperature sodium-sulfur batteries (NaSBs) is polysulfide dissolution and shuttling, which results in irreversible capacity decay and low Coulombic efficiencies. In this work, we demonstrate for the first time NaSBs using a ferrocene-derived amorphous sulfurized cyclopentadienyl composite (SCC) cathode. Polysulfide dissolution is eliminated via covalent bonding between the insoluble short-chain sulfur species and carbon backbone. Control experiments with a metal-free composite analogue determined that the iron species in the SCC does not have a significant role in polysulfide anchoring. Instead, the superior electrochemical performance is attributed to sulfur covalently bonded to carbon and the uniform nanoparticulate morphology of the SCC composite. In the carbonate-based electrolyte, a discharge capacity of 795 mAh g(S)-1 was achieved during early cycling at 0.2 C, and high Coulombic efficiencies close to 100% were maintained with capacity retention of 532 and 442 mAh g(S)-1 after 100 and 200 cycles, respectively.

Tunable Nitrogen-Doping of Sulfur Host Nanostructures for Stable and Shuttle-Free Room-Temperature Sodium-Sulfur Batteries.

Room-temperature sodium-sulfur batteries have potential in stationary applications, but challenges such as loss of active sulfur and low electrical conductivity must be solved. Nitrogen-doped nanocarbon host cathodes have been employed in metal-sulfur batteries: polar interactions mitigate the loss of sulfur, while the conductive nanostructure addresses the low conductivity. Nevertheless, these two properties run contrary to each other as greater nitrogen-doping of nanocarbon hosts is associated with lower conductivity. Herein, we investigate the polarity-conductivity dilemma to determine which of these properties have the stronger influence on cycling performance. Lower carbonization temperatures produce more pyridinic nitrogen and pyrrolic nitrogen, which from density functional theory calculations preferentially bind discharge products (Na2S and short-chain polysulfides). Despite its lower conductivity, the highly doped composite showed better Coulombic efficiency and stability, retaining a high capacity of 980 mAh g(S)-1 after 800 cycles. Our findings represent a paradigm shift where nitrogen-doping should be prioritized in designing shuttle-free, long-life sodium-sulfur batteries.