Photoelectrocatalysis Synthesis of Ammonia Based on a Ni-Doped MoS2/Si Nanowires Photocathode and Porous Water with High N2 Solubility

Paired Chemical Upgrading in Photoelectrochemical Cells

Photoelectrochemical (PEC) technology has emerged as a promising platform for sustainable energy conversion and chemical synthesis, utilizing solar energy to facilitate redox reactions. While PEC systems have been extensively studied for water splitting, CO2 reduction, nitrogen reduction for value-added compounds synthesis, the sluggish oxygen evolution reaction (OER) on the anode side and the less economic value of O2 limit system efficiency. To address this, researchers have explored paired chemical upgrading strategies, coupling selective anodic organic oxidation reactions (OORs) with cathodic reduction reactions. This approach enabled the simultaneous production of high-value chemicals and fuels, enhancing the PEC system efficiency and economic viability. In this Perspective, we highlight the latest advancements and milestones in coupling anode OORs and cathode reduction reactions within PEC cells. Particular emphasis is placed on the key design principles, catalyst development, reaction mechanisms, and the performance of paired PEC cells. In addition, challenges and perspectives are provided for the future development of this emerging and sustainable technology.

Low-dimensional materials for ammonia synthesis

Ammonia is an essential chemical due to its immense usage in agriculture, energy storage, and transportation. The synthesis of "green" ammonia via carbon-free routes and renewable energy sources is the need of the hour. In this context, photo- and/or electrocatalysis proves to be highly crucial. Low-dimensional materials (LDMs), owing to their unique properties, play a significant role in catalysis. This review presents a vast library of LDMs and broadly categorizes their catalytic performance according to their dimensionality, i.e., zero-, one-, and two-dimensional catalysts. The rational design of LDMs can significantly improve their catalytic performance, particularly in reducing small molecules like dinitrogen, nitrates, nitrites, and nitric oxides to synthesize ammonia via photo- and/or electrocatalysis. Additionally, converting nitrates and nitrites to ammonia can be beneficial in wastewater treatment and be coupled with CO2 co-reduction or oxidative reactions to produce urea and other valuable chemicals, which are also discussed in this review. This review collates the works published in recent years in this field and offers some fresh perspectives on ammonia synthesis. Through this review, we aim to provide a comprehensive insight into the catalytic properties of the LDMs, which are expected to enhance the efficiency of ammonia production and promote the synthesis of value-added products.

A biofuel cell of (methyl violet/AuNPs)25/FTO photoanode and bilirubin oxidase/CuCo2O4 bio-photocathode inspired by the photoelectrochemistry activities of fluorescent materials/molecules

Herein, we discuss the idea that fluorescent materials/molecules should logically show potential photoelectrochemistry (PEC) activity, and, in particular, the PEC of fluorescent small molecules (previously usually acting only as dye sensitizers for conventional semiconductors) is explored. After examining the PEC activities of some typical inorganic or organic fluorescent materials/molecules and by adopting methyl violet (MV) with the highest PEC activity among the examined fluorescent small molecules, a new and efficient (MV/Au nanoparticles (AuNPs))25/fluorine-doped tin oxide (FTO) photoanode without conventional semiconductor(s) is prepared by layer-by-layer alternating the electrodeposition of AuNPs and the adsorption of MV. A bilirubin oxidase (BOD)/CuCo2O4/FTO bio-photocathode is prepared by electrodeposition, calcination and cast-coating. Under optimal conditions, a new photoelectrochemical enzymatic biofuel cell (PEBFC) consisting of this photoanode in 0.1 M phosphate buffer solution (PBS) containing 0.1 M ascorbic acid, this bio-photocathode in 0.1 M PBS containing 0.5 mM 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, and a Nafion membrane gives an open-circuit voltage of 0.73 V and a maximum power output density of 14.1 μW cm-2, outperforming many reported comparable enzymatic biofuel cells. This fluorescence-activity-based PEC research suggests that new PEC and photocatalysis materials/molecules may be found from the huge library of fluorescent substances, and such a fluorescence-based reference criterion is of some general reference value for exploring potential photoelectric materials/molecules and expanding the applications of fluorescent substances.

Key developments in magnesiothermic reduction of silica: insights into reactivity and future prospects

Porous Si (p-Si) nanomaterials are an exciting class of inexpensive and abundant materials within the field of energy storage. Specifically, p-Si has been explored in battery anodes to improve charge storage capacity, to generate clean fuels through photocatalysis and photoelectrochemical processes, for the stoichiometric conversion of CO2 to value added chemicals, and as a chemical H2 storage material. p-Si can be made from synthetic, natural, and waste SiO2 sources through a facile and inexpensive method called magnesiothermic reduction (MgTR). This yields a material with tunable properties and excellent energy storage capabilities. In order to tune the physical properties that affect performance metrics of p-Si, a deeper understanding of the mechanism of the MgTR and factors affecting it is required. In this perspective, we review the key developments in MgTR and discuss the thermal management strategies used to control the properties of p-Si. Additionally, we explore future research directions and approaches to bridge the gap between laboratory-scale experiments and industrial applications.

Modulating band structure through introducing Cu0/CuxO composites for the improved visible light driven ammonia synthesis

The photocatalytic performance of ceria-based materials can be tuned by adjusting the surface structures with decorating the transition-metal, which are considered as the important active sites. Herein, cuprous oxide-metallic copper composite-doped ceria nanorods were assembled through a simple hydrothermal reduction method. The photocatalytic ammonia synthesis rates exhibit an inverted "V-shaped" trend with increasing Cu0/CuxO mole ratio. The best ammonia production rate, approximately 900 or 521 µmol·gcal-1·h-1 under full-spectra or visible light, can be achieved when the Cu0/CuxO ratio is approximately 0.16, and this value is 8 times greater than that of the original sample. The absorption edge of the as-prepared samples shifted towards visible wavelengths, and they also had appropriate ammonia synthesis levels. This research provides a strategy for designing noble metal-free photocatalysts through introducing the metal/metallic oxide compositesto the catalysts.

Frontiers in Photoelectrochemical Catalysis: A Focus on Valuable Product Synthesis

Photoelectrochemical (PEC) catalysis provides the most promising avenue for producing value-added chemicals and consumables from renewable precursors. Over the last decades, PEC catalysis, including reduction of renewable feedstock, oxidation of organics, and activation and functionalization of C─C and C─H bonds, are extensively investigated, opening new opportunities for employing the technology in upgrading readily available resources. However, several challenges still remain unsolved, hindering the commercialization of the process. This review offers an overview of PEC catalysis targeted at the synthesis of high-value chemicals from sustainable precursors. First, the fundamentals of evaluating PEC reactions in the context of value-added product synthesis at both anode and cathode are recalled. Then, the common photoelectrode fabrication methods that have been employed to produce thin-film photoelectrodes are highlighted. Next, the advancements are systematically reviewed and discussed in the PEC conversion of various feedstocks to produce highly valued chemicals. Finally, the challenges and prospects in the field are presented. This review aims at facilitating further development of PEC technology for upgrading several renewable precursors to value-added products and other pharmaceuticals.

Tuning Surface Electronics State of P-Doped In2.77S4/In(OH)3 toward Efficient Photoelectrochemical Water Oxidation

Indium sulfide with a two-dimensional layered structure offers a platform for catalyzing water oxidation by a photoelectrochemical process. However, the limited hole holders hinder the weak intrinsic catalytic activity. Here, the nonmetallic phosphorus atom is coordinated to In2.77S4/In(OH)3 through a bridge-bonded sulfur atom. By substituting the S position by the P dopant, the work function (surface potential) is regulated from 445 to 210 mV, and the lower surface potential is shown to be beneficial for holding the photogenerated holes. In2.77S4/In(OH)3/P introduces a built-in electric field under the difference of Fermi energy, and the direction is from the bulk to the surface. This band structure results in upward band bending at the interface of In2.77S4/In(OH)3 and P-doped sites, which is identified by density functional theory calculations (∼0.8 eV work function difference). In2.77S4/In(OH)3/P stands out with the highest oxidation efficiency (ηoxi = 70%) and charge separation efficiency (ηsep = 69%). Importantly, it delivers a remarkable water oxidation photocurrent density of 2.51 mA cm-2 under one sun of illumination.