• Energy Research

The ice-templated method (ITM) has drawn significant attention to the improvement of the electrochemical properties of various materials. The ITM approach is relatively straightforward and can produce hierarchically porous structures that exhibit superior performance in mass transfer, and the unique morphology has been shown to significantly enhance electrochemical performance, making it a promising method for energy storage and conversion applications. In this review, we aim to present an overview of the ITM and its applications in the electrochemical energy storage and conversion field. The fundamental principles underlying the ITM will be discussed, as well as the factors that influence the morphology and properties of the resulting structures. We will then proceed to comprehensively explore the applications of ITM in the fabrication of high-performance electrodes for supercapacitors, batteries, and fuel cells. We intend to find the key advances in the use of ITM and evaluate its potential to overcome the existing challenges in the development of efficient energy storage and conversion systems.

The urea oxidation reaction (UOR), requiring less energy to produce hydrogen, is considered as a potential alternative to the traditional oxygen evolution reaction. Consequently, developing highly efficient UOR catalysts to facilitate H2 production has garnered widespread attention. A promising approach to enhancing the effectiveness of these electrocatalysts is defect engineering. By introducing structural defects, defect engineering can expose more active sites and optimize their electronic structure, thereby improving their activity. This work offers a comprehensive overview of recent progress in defect engineering of nickel-based electrocatalysts for the UOR. It summarizes various strategies for generating defects, including the creation of vacancies, doping, the incorporation of single atoms, amorphization, and achieving high refractivity. Furthermore, we discuss the advanced characterization techniques commonly used to identify the presence of defects in these electrocatalysts, as well as to determine their detailed structures. Finally, we outline the prospects and challenges associated with the systematic design and fabrication of novel UOR electrocatalysts with tunable defects, aiming to further enhance their efficiency and stability.

AbstractUrea is an important chemical in agricultural, biosystem and chemical engineering. It can not only be a fertilizer and feed supplement, but also converted into electricity and hydrogen based on the counterpart half‐reactions. In this concept, we demonstrated the fundamental mechanism of electrochemical urea oxidation reaction (UOR) and its various applications on environmental, energy and healthcare devices with typical examples. UOR providing potential directions for the electrochemical treatment of urea‐contained wastewater were also introduced in this concept. This work is not focused on electrocatalyst design, but rather offers instructive guidance for the UOR developments in environmental, energy, and healthcare devices.

Two-dimensional transition metal borides (MBenes) have emerged as promising electrocatalysts for hydrogen evolution reactions (HERs), attracting significant research interest due to theoretical computations that enhance the understanding and optimization of their performance. This review begins with a comprehensive summary of HER mechanisms, followed by an in-depth examination of the geometric and electronic properties of MBenes. Subsequently, this review explores MBene-based electrocatalysts for HERs, employing free-energy diagrams and an electronic structure analysis to assess both the intrinsic catalytic activity of MBenes and the theoretical performance of single-atom modified MBenes. Finally, the prospects and challenges associated with MBenes are discussed, providing valuable insights to guide future research in this area. Overall, this topic holds significant relevance for researchers in the HER field, and this review aims to deliver theoretical insights for the optimal design of advanced MBene electrocatalysts.

Accurate acetaminophen (APAP) determination using smartphone-based portable sensing hinges on developing sensing interfaces with effective catalytic performance and high electron transfer efficiency. Herein, we report that various Ni-based bimetallic-organic framework materials (MOFs) were synthesized through the hydrothermal method. These MOFs were incorporated with multiwalled carbon nanotubes (MWCNTs) during the synthesis of chitosan-cationic guar gum hydrogels (HG). The resulting composite conductive hydrogel features a distinctive three-dimensional network structure with a large specific surface area, enhancing APAP enrichment and electrocatalytic activity. Among them, CuNi-MOF-based chitosan-cationic guar gum conductive hydrogel (CHG/CuNi-MOF) has the most desirable capability as a signal amplifier. Under optimal conditions, the sensor constructed with the screen-printed electrode (SPE) using CHG/CuNi-MOF (CHG/CuNi-MOF/SPE) has a wide detection range (0.07-1500 μM), a low detection limit (0.023 μM), and a relatively high sensitivity (0.0450 μA·μM-1·cm-2) for the APAP determination. In addition, CHG/CuNi-MOF/SPE has good stability, repeatability and anti-interference properties, which make it possible to achieve selective determination of targets in complex analysis and ultimately obtain satisfactory recoveries (97.6-104.2%). This work successfully proves the feasibility of the application of MOFs-based conductive hydrogel in the electrochemical detection of phenolics in actual samples.

Biomass-derived carbon dots (CDs) are non-toxic and fluorescently stable, making them suitable for extensive application in fluorescence sensing. The use of cheap and renewable materials not only improves the utilization rate of waste resources, but it is also drawing increasing attention to and interest in the production of biomass-derived CDs. Visual fluorescence detection based on CDs is the focus of current research. This method offers high sensitivity and accuracy and can be used for rapid and accurate determination under complex conditions. This paper describes the biomass precursors of CDs, including plants, animal remains and microorganisms. The factors affecting the use of CDs as fluorescent probes are also discussed, and a brief overview of enhancements made to the preparation process of CDs is provided. In addition, the application prospects and challenges related to biomass-derived CDs are demonstrated.

Schematic of preparation of N-CDs and their sensing mechanism for sunset yellow.

AbstractDeveloping efficient electrocatalysts with low‐cost for the urea oxidation reaction (UOR) is a significant challenge in energy‐saving H2 production owing to its lower thermodynamic potential. Heteroatom incorporation strategy has been proven to boost electrocatalytic activity by altering electronic structures and revealing more active sites on catalysts. Herein, nickel hydroxide nanosheets with various vanadium incorporation (Vx‐Ni(OH)2) were developed through a facile hydrothermal approach. By optimizing the incorporated vanadium contents, V6‐Ni(OH)2 catalyst exhibited easily accessible active sites and enhanced charge transfer with structural advantages, then assembled as the working electrode for urea‐assisted H2 production. Consequently, V6‐Ni(OH)2 catalyst demonstrated superior UOR activity compared with other incorporated samples with an overpotential of 1.33 V and a Tafel slope of 28.3 mV dec−1. Theoretical calculations revealed that the improved UOR activity was attributed to the potential determining step of V‐Ni(OH)2, which exhibited lower energy in comparison with the pristine Ni(OH)2 and increased electronic states density near the Fermi level. Both experimental and theoretical calculations confirmed vanadium incorporation on Ni(OH)2 could modify the electronic structure of Ni(III) species, improving electrical conductivity, and optimizing the adsorption energy for key reaction intermediates. Furthermore, the crucial contribution of vanadium incorporation with optimized electronic structures to the high UOR activity of Ni(OH)2 is demonstrated.image

Heteroatom doping is an effective strategy to regulate electrocatalysts for the oxygen evolution reaction (OER). Nonmetal heteroatoms can effectively engineer geometric and electronic structures and activating surface sites of catalysts due to their unique radius and the electronegativity of nonmetal atoms. Hence, the surface geometric and electronic structure and activity of nonmetal atoms (X, X = B, C, N, O, P)-doped Ni3S2 (X-Ni3S2) were studied to screen high-performance Ni3S2-based OER electrocatalysts through density functional theory calculation. Theoretical results demonstrated that dopants in X-Ni3S2 can alter bond length and charge of surface, modify active sites for intermediates adsorption, and adjust the theoretical overpotential. Among all dopants, C can effectively modulate surface structure, activate surface sites, weaken the adsorption of key intermediates, decrease theoretical overpotential, and enable C-Ni3S2 with the best theoretical OER activity among all X-Ni3S2 with the lowest theoretical overpotential (0.46 eV). Further experimental results verified that the synthesized C-Ni3S2 performed an improved OER activity in the alkaline condition with a considerably enhanced overpotential of 261 mV at 10 mA cm−2 as well as a Tafel slope of 95 mV dec−1 compared to pristine Ni3S2.