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The excessive energy demand of the conventional Haber–Bosch process for ammonia (NH3) generation, coupled with the disruptive effects of nitrate (NO3−) pollution on the global nitrogen cycle, has made the electrocatalytic nitrate reduction reaction (NO3−RR) an essential exit strategy for sustainable NH3 synthesis. However, the intricate multi-step proton and electron transfer process posed a great challenge in achieving high-efficiency electrocatalysts. In this study, we report a selective and highly active NO3−RR electrocatalyst featuring molecular M–Nx sites derived from the immobilization of Fe ions within N-doped graphene quantum dots (NGQDs). We demonstrated that the formation of molecular Fe–Nx coordination activated the NO3−RR of NGQDs-Fe, despite the initial inactivity of NGQDs. In situ Raman analysis revealed that those Fe–Nx sites served as favourable adsorption sites for *NO3. Such catalyst achieved an FE of 93% and a yield rate of 15.41 mmol h−1 cm−2 for NH3 at −0.8 V (vs. RHE) in an alkaline medium. These findings revealed the preferential sequential 2e− and 6e− transfer pathways over the direct 8e− pathway in the NO3−RR, which provides new mechanistic insights into the nitrate reduction reaction. [ABSTRACT FROM AUTHOR]

Rapid interest in identifying specific biomarkers has been sparked by the development of wearable electrochemical sensors for physiological and biological monitoring via noninvasive measurement. During anaerobic metabolic circumstances, monitoring the lactate content become critical for noninvasive diagnostic of hypoxia. To improve the sensitivity of wearable sweat biosensors for detecting lactate concentrations, in this study, metal–organic framework (MOF)-derived NiCo-based layered double hydroxides (m-NiCo LDHs) with N-doped graphene quantum dots (NGQDs) decoration are designed. According to the X-ray absorption spectroscopy (XAS) analysis, the incorporation of NGQDs will alter the local electronic structure of transition metals in m-NiCo LDHs, thereby reducing the charge transfer resistance and accelerating the electron transfer kinetics during electrochemical reactions of lactate detection. After understanding the role of NGQDs in the matrix of m-NiCo LDHs, as-designed NGQD/m-NiCo LDH-based electrochemical biosensors for lactate detection displayed superior sensitivity of 62.63 ± 1.50 μA mM–1 cm–2 under an applied potential of 0.60 V (vs Ag/AgCl/3 M KCl) with the lactate concentration range of 0 to 15 mM in alkaline condition, compared to pristine NiCo LDH (16.77 ± 1.70 μA mM–1 cm–2)- and m-NiCo LDH (45.45 ± 4.39 μA mM–1 cm–2)-based ones. This research provides a potential electrocatalyst of GQD-modified MOF-derived LDHs for using enzyme-free electrochemical lactate sensors with reliable and stable performance in order to implement noninvasive human perspiration monitoring on wearable bioelectronics. [ABSTRACT FROM AUTHOR]

A photoelectrochromic device (PECD) is a combination of a dye-sensitized solar cell (DSSC) and an electrochromic device (ECD) that directly generates transmittance contrast from solar radiation without an additional power source. In terms of application, PECDs have recently been utilized as self-powered smart windows for eco-friendly green buildings. The majority of PECDs have exceptional optical performance in the visible light region, with their electrochromic property regulating the indoor luminance. Nonetheless, indoor temperature regulation is also a potential opportunity that might be examined further for PECDs. As the temperature is highly correlated with the incident flux of infrared light, this study presents a near-infrared photoelectrochromic device (NIR-PECD) with WO3 as the electrochromic material for blocking infrared radiation, realizing indoor thermal management without external power. The NIR-PECD exhibited the ability of thermal modulation and lowered the indoor temperature with a transmittance contrast in the NIR region, demonstrating a transmittance contrast (ΔT) of 40.2% and an outstanding photocoloration efficiency (PhCE) of 55.85 cm2 min−1 W−1 at the wavelength of 1000 nm. In addition, the NIR-PECD also displayed a 5.6 °C temperature difference between the colored and bleached states, indicating the thermal management capabilities of keeping the interior cool in the colored state by blocking the NIR. As a further application, NIR-PECDs can be used as self-powered smart windows in green buildings to achieve internal temperature control without external power. [ABSTRACT FROM AUTHOR]

Flower-like phosphorus-doped nickel oxide (P-NiO) is proposed as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). The flower-like nickel oxide essentially serves as the matrix for the CE, which is expected to promote a two-dimensional electron transport pathway. The phosphorus is intended to improve the catalytic ability by creating more active sites in the NiO for the catalysis of triiodide ions (I3−) to iodide ions (I−) on the surface of the CE. The P-NiO is controlled by a sequencing of precursor concentration, which allows the P-NiO to possess different features. The debris aggregation occurs in the P-NiO-1, while the P-NiO-0.75 leads to the incomplete flower-like nanosheets. The complete flower-like morphology can be observed in the P-NiO-0.5, P-NiO-0.25 and P-NiO-0.1 catalytic electrodes. The DSSC with the P-NiO-0.5 CE achieves a power conversion efficiency (η) of 9.05%, which is better than that of the DSSC using a Pt CE (η = 8.51%); it also performs better than that with the Pt CE, even under rear illumination and dim light conditions. The results indicate the promising potential of the P-NiO CE to replace the expensive Pt CE. [ABSTRACT FROM AUTHOR]

Recently, urea electrolysis has been regarded as an up-and-coming pathway for the sustainability of hydrogen fuel production according to its far lower theoretical and thermodynamic electrolytic cell potential (0.37 V) compared to water electrolysis (1.23 V) and rectification of urea-rich wastewater pollution. The new era of the "hydrogen energy economy" involving urea electrolysis can efficiently promote the development of a low-carbon future. In recent decades, numerous inexpensive and fruitful nickel-based materials (metallic Ni, Ni-alloys, oxides/hydroxides, chalcogenides, nitrides and phosphides) have been explored as potential energy saving monofunctional and bifunctional electrocatalysts for urea electrolysis in alkaline solution. In this review, we start with a discussion about the basics and fundamentals of urea electrolysis, including the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER), and then discuss the strategies for designing electrocatalysts for the UOR, HER and both reactions (bifunctional). Next, the catalytic performance, mechanisms and factors including morphology, composition and electrode/electrolyte kinetics for the ameliorated and diminished activity of the various aforementioned nickel-based electrocatalysts for urea electrolysis, including monofunctional (UOR or HER) and bifunctional (UOR and HER) types, are summarized. Lastly, the features of persisting challenges, future prospects and expectations of unravelling the bifunctional electrocatalysts for urea-based energy conversion technologies, including urea electrolysis, urea fuel cells and photoelectrochemical urea splitting, are illuminated. [ABSTRACT FROM AUTHOR]

Emerging wearable devices with noninvasive biosensing technologies have sparked substantial interest for constant monitoring of substances in bodily fluids, which might be used to detect human health issues. Uric acid (UA) is a crucial indicator of a high relationship with gout, hyperuricemia, and Lesch–Nyhan syndrome. Therefore, developing a wearable device to noninvasively monitor the UA levels in sweat has drawn enormous attention. In this work, boron-doped graphene quantum dots anchored to carbon nanotubes (BGQDs/CNTs) were proposed as noble-metal-free electrocatalysts for the design of the enzyme-free wearable sensors to monitor the concentration of UA in human sweat. BGQDs could provide extra active sites to enhance the electrocatalytic ability of the UA oxidation reaction. From the results, BGQDs/CNTs exhibit ultrahigh sensitivity of 8.92 ± 0.22 μA μM–1 cm–2 for UA detection compared to pristine CNTs (4.24 ± 0.24 μA μM–1 cm–2). Moreover, density functional theory calculations indicate that B atoms can strengthen the UA molecule adsorption and enlarge electron transfer from the UA molecule to the B-doped graphene sheet, supporting the high sensitivity of BGQDs for UA detection. Hence, this study offers a promising electrocatalyst for using an enzyme-free electrochemical UA sensor with a dependable and steady performance to further the use of wearable electronics. [ABSTRACT FROM AUTHOR]