Additive Manufacturing: A Paradigm Shift in Revolutionizing Catalysis with 3D Printed Photocatalysts and Electrocatalysts Toward Environmental Sustainability.

Semiconductor-based materials utilized in photocatalysts and electrocatalysts present a sophisticated solution for efficient solar energy utilization and bias control, a field extensively explored for its potential in sustainable energy and environmental management. Recently, 3D printing has emerged as a transformative technology, offering rapid, cost-efficient, and highly customizable approaches to designing photocatalysts and electrocatalysts with precise structural control and tailored substrates. The adaptability and precision of printing facilitate seamless integration, loading, and blending of diverse photo(electro)catalytic materials during the printing process, significantly reducing material loss compared to traditional methods. Despite the evident advantages of 3D printing, a comprehensive compendium delineating its application in the realm of photocatalysis and electrocatalysis is conspicuously absent. This paper initiates by delving into the fundamental principles and mechanisms underpinning photocatalysts electrocatalysts and 3D printing. Subsequently, an exhaustive overview of the latest 3D printing techniques, underscoring their pivotal role in shaping the landscape of photocatalysts and electrocatalysts for energy and environmental applications. Furthermore, the paper examines various methodologies for seamlessly incorporating catalysts into 3D printed substrates, elucidating the consequential effects of catalyst deposition on catalytic properties. Finally, the paper thoroughly discusses the challenges that necessitate focused attention and resolution for future advancements in this domain.

Point-Defect Engineering: Leveraging Imperfections in Graphitic Carbon Nitride (g-C3 N4 ) Photocatalysts toward Artificial Photosynthesis.

Graphitic carbon nitride (g-C3 N4 ) is a kind of ideal metal-free photocatalysts for artificial photosynthesis. At present, pristine g-C3 N4 suffers from small specific surface area, poor light absorption at longer wavelengths, low charge migration rate, and a high recombination rate of photogenerated electron-hole pairs, which significantly limit its performance. Among a myriad of modification strategies, point-defect engineering, namely tunable vacancies and dopant introduction, is capable of harnessing the superb structural, textural, optical, and electronic properties of g-C3 N4 to acquire an ameliorated photocatalytic activity. In view of the burgeoning development in this pacey field, a timely review on the state-of-the-art advancement of point-defect engineering of g-C3 N4 is of vital significance to advance the solar energy conversion. Particularly, insights into the intriguing roles of point defects, the synthesis, characterizations, and the systematic control of point defects, as well as the versatile application of defective g-C3 N4 -based nanomaterials toward photocatalytic water splitting, carbon dioxide reduction and nitrogen fixation will be presented in detail. Lastly, this review will conclude with a balanced perspective on the technical and scientific hindrances and future prospects. Overall, it is envisioned that this review will open a new frontier to uncover novel functionalities of defective g-C3 N4 -based nanostructures in energy catalysis.

Isotype heterojunction: tuning the heptazine/triazine phase of crystalline nitrogen-rich C3N5 towards multifunctional photocatalytic applications.

Photocatalytic technology has been well studied as a means to achieve sustainable energy generation through water splitting or chemical synthesis. Recently, a low C/N atomic ratio carbon nitride allotrope, C3N5, has been found to be highly prospective due to its excellent electronic properties and ample N-active sites compared to g-C3N4. Tangentially, crystalline g-C3N4 has also been a prospective candidate due to its improved electron transport and extended π-conjugated system. For the first time, our group successfully employed a one-step molten salt calcination method to prepare novel N-rich crystalline C3N5 and elucidate the effect of calcination temperature on the heptazine/triazine phase. Calcination temperatures of 500 °C (CC3N5-500) and 550 °C (CC3N5-550) lead to crystalline carbon nitride with both heptazine and triazine phases, forming an intimate isotype heterojunction for robust interfacial charge separation. An excellent photocatalytic hydrogen evolution rate (359.97 µmol h-1; apparent quantum efficiency (AQE): 12.86% at 420 nm) was achieved using CC3N5-500, which was 15-fold higher than that of pristine C3N5. Furthermore, CC3N5-500 exhibited improved activity for simultaneous benzyl alcohol oxidation and hydrogen production, as well as H2O2 production (AQE: 9.49% at 420 nm), signifying its multitudinous photoredox capabilities. Moreover, the recyclability tests of the optimal CC3N5-500 on a 3D-printed substrate also showed a 92% performance retention after 4 cycles (16 h). This highlights that crystalline C3N5 significantly augmented the reaction performance for diverse multifunctional solar-driven applications. As such, these results serve as a guide toward the structural tuning of 2D metal-free carbon nanomaterials with tunable crystallinity toward achieving boosted photocatalysis.

Mechanistic study of the competition between carbon dioxide reduction and hydrogen evolution reaction and selectivity tuning via loading single-atom catalysts on graphitic carbon nitride.

In the context of catalytic CO2 reduction (CO2RR), the interference of the inherent hydrogen evolution reaction (HER) and the possible selectivity towards CO have posed a significant challenge to the generation of formic acid. To address this hurdle, in this work, we have investigated the impact of different single-atom metal catalysts on tuning selectivity by employing density functional theory (DFT) calculations to scrutinize the reaction pathways. Single-atom catalysts supported on carbon-based systems have proven to be pivotal in altering both the activity and selectivity of the CO2RR. In this study, a series of single-atom-metal-loaded g-C3N4 monolayers (MCN, M = Ni, Cu, Zn, Ga, Cd, In, Sn, Pb, Ag, Au, Bi, Pd and Pt) were systematically examined. Through detailed DFT calculations, we explored their influence on reaction selectivity between the *COOH and *OCHO intermediates. Notably, NiCN favors the reaction via the *OCHO route, with a significantly lower rate-determining potential of 0.36 eV, which is approximately 73.5% lower than that of the CN system (1.36 eV). Most importantly, the Ni single-atom catalyst with lower coordination significantly enhances CO2 adsorption, promoting CO2RR over HER. Overall, this study, guided by DFT calculations, provides a theoretical prediction of how the selection of single-atom metal catalysts can effectively modulate the reaction pathway, thereby offering a potential solution for achieving high product selectivity in CO2RR.

A Prospective Life Cycle Assessment of Electrochemical CO2 Reduction to Selective Formic Acid and Ethylene.

Invited for this month's cover is the group of Prof. Dr. Wee-Jun Ong at Xiamen University Malaysia. The image shows a model of Xiamen University and is in celebration of the 5th and 100th anniversary of Xiamen University Malaysia and Xiamen University, respectively. The cover showcases the institutes as a pillar of renewable nanotechnology research and a key player in the ever-growing search for sustainable energy. The Research Article itself is available at 10.1002/cssc.202200857.

A Prospective Life Cycle Assessment of Electrochemical CO2 Reduction to Selective Formic Acid and Ethylene.

Converting CO2 into valuable C1 -C2 chemicals through electrochemical CO2 reduction (ECR) has potential to remedy the ever-increasing climate problems owing to the intensification of industrial activity. In this work, cradle-to-gate life cycle assessment (LCA) was performed to quantify the environmental impacts of formic acid (FA) and ethylene production through ECR benchmarked with the conventional processes. At the midpoint level, global warming potential (GWP) effects of FA and ethylene production through ECR recorded 5.6 and 1.6-times that of the conventional process, respectively. Although ECR currently has limited environmental benefits, the incorporation of hydropower has vast potential after evaluating four sustainable electricity sources, namely hydropower, wind, solar, and biomass. Notably, ECR to FA recorded a 24 % reduction in petrochemical usage. For ethylene production, human health damage, ecosystem damage, and petrochemical use were reduced by 67, 94, and 110 %, respectively. Sensitivity analysis indicated that a sustainable energy supply chain for ECR will accelerate the development of a circular economy.

Life cycle assessment of environmental impacts associated with oxidative desulfurization of diesel fuels catalyzed by metal-free reduced graphene oxide.

This study aimed to analyze the environmental impacts of the oxidative desulfurization (ODS) process catalyzed by metal-free reduced graphene oxide (rGO) through life cycle assessment (LCA). The environmental impacts study containing the rGO production process, the ODS process, the comparison of different oxidants and solvents was developed. This study was performed by using ReCiPe 2016 V1.03 Hierarchist midpoint as well as endpoint approach and SimaPro software. For the production of 1 kg rGO, the results showed that hydrochloric acid (washing), sulfuric acid (mixing), hydrazine (reduction) and electricity were four main contributors in this process, and this process showed a significant impact on human health 14.21 Pt followed by ecosystem 0.845 Pt and resources 0.164 Pt. For the production of 1 kg desulfurized oil (400 ppm), main environmental impacts were terrestrial ecotoxicity (43.256 kg 1,4-DCB), global warming (41.058 kg CO2), human non-carcinogenic toxicity (19.570 kg 1,4-DCB) and fossil resource scarcity (13.178 kg oil), and the main contributors were electricity, diesel oil and acetonitrile. The whole ODS process also showed a greatest effect on human health. For two common oxidants hydrogen peroxide and oxygen used in ODS, hydrogen peroxide showed a greater impact than oxygen. On the other hand, for three common solvents employed in ODS, N-methyl-2-pyrrolidone had a more serious impact on human health followed by acetonitrile and N,N-dimethylformamide. As such, LCA results demonstrated the detailed environmental impacts originated from the catalytic ODS, hence elucidating systematic guidance for its future development toward practicality.

Lithium-Sulfur Battery Cathode Design: Tailoring Metal-Based Nanostructures for Robust Polysulfide Adsorption and Catalytic Conversion.

Lithium-sulfur (Li-S) batteries have a high specific energy capacity and density of 1675 mAh g-1 and 2670 Wh kg-1 , respectively, rendering them among the most promising successors for lithium-ion batteries. However, there are myriads of obstacles in the practical application and commercialization of Li-S batteries, including the low conductivity of sulfur and its discharge products (Li2 S/Li2 S2 ), volume expansion of sulfur electrode, and the polysulfide shuttle effect. Hence, immense attention has been devoted to rectifying these issues, of which the application of metal-based compounds (i.e., transition metal, metal phosphides, sulfides, oxides, carbides, nitrides, phosphosulfides, MXenes, hydroxides, and metal-organic frameworks) as sulfur hosts is profiled as a fascinating strategy to hinder the polysulfide shuttle effect stemming from the polar-polar interactions between the metal compounds and polysulfides. This review encompasses the fundamental electrochemical principles of Li-S batteries and insights into the interactions between the metal-based compounds and the polysulfides, with emphasis on the intimate structure-activity relationship corroborated with theoretical calculations. Additionally, the integration of conductive carbon-based materials to ameliorate the existing adsorptive abilities of the metal-based compound is systematically discussed. Lastly, the challenges and prospects toward the smart design of catalysts for the future development of practical Li-S batteries are presented.