Helpful elements: A facile bottom-up method using citric acid and L-cysteine as a precursor has been developed to prepare graphene quantum dots (GQDs) co-doped with nitrogen and sulfur. A new type and high density of surface state of GQDs arises, leading to high yields (more than 70 %) and excitation-independent emission. FLQY = fluorescence quantum yield.

Over the past few decades, the design and development of advanced electrocatalysts for efficient energy conversion technologies have been subjects of extensive study. With the discovery of graphene, two-dimensional (2D) nanomaterials have emerged as some of the most promising candidates for heterogeneous electrocatalysts due to their unique physical, chemical, and electronic properties. Here, we review 2D-nanomaterial-based electrocatalysts for selected electrocatalytic processes. We first discuss the unique advances in 2D electrocatalysts based on different compositions and functions followed by specific design principles. Following this overview, we discuss various 2D electrocatalysts for electrocatalytic processes involved in the water cycle, carbon cycle, and nitrogen cycle from their fundamental conception to their functional application. We place a significant emphasis on different engineering strategies for 2D nanomaterials and the influence these strategies have on intrinsic material performance, such as electronic properties and adsorption energetics. Finally, we feature the opportunities and challenges ahead for 2D nanomaterials as efficient electrocatalysts. By considering theoretical calculations, surface characterization, and electrochemical tests, we describe the fundamental relationships between electronic structure, adsorption energy, and apparent activity for a wide variety of 2D electrocatalysts with the goal of providing a better understanding of these emerging nanomaterials at the atomic level.

This perspective highlights the rational design of efficient electrocatalysts and photo(electro)catalysts for N2 reduction to ammonia (NH3) under ambient conditions.

Developing cost-effective and high-performance electrocatalysts for renewable energy conversion and storage is motivated by increasing concerns regarding global energy security and creating sustainable technologies dependent on inexpensive and abundant resources. Recent achievements in the design and synthesis of efficient non-precious-metal and even non-metal electrocatalysts make the replacement of noble metal counterparts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) with earth-abundant elements, for example, C, N, Fe, Mn, and Co, a realistic possibility. It has been found that surface atomic engineering (e.g., heteroatom-doping) and interface atomic or molecular engineering (e.g., interfacial bonding) can induce novel physicochemical properties and strong synergistic effects for electrocatalysts, providing new and efficient strategies to greatly enhance the catalytic activities. In this Account, we discuss recent progress in the design and fabrication of efficient electrocatalysts based on carbon materials, graphitic carbon nitride, and transition metal oxides or hydroxides for efficient ORR, OER, and HER through surface and interfacial atomic and molecular engineering. Atomic and molecular engineering of carbon materials through heteroatom doping with one or more elements of noticeably different electronegativities can maximally tailor their electronic structures and induce a synergistic effect to increase electrochemical activity. Nonetheless, the electrocatalytic performance of chemically modified carbonaceous materials remains inferior to that of their metallic counterparts, which is mainly due to the relatively limited amount of electrocatalytic active sites induced by heteroatom doping. Accordingly, coupling carbon substrates with other active electrocatalysts to produce composite structures can impart novel physicochemical properties, thereby boosting the electroactivity even further. Although the majority of carbon-based materials remain uncompetitive with state-of-the-art metal-based catalysts for the aforementioned catalytic processes, non-metal carbon hybrids have already shown performance that typically only conventional noble metals or transition metal materials can achieve. The idea of hybridized carbon-based catalysts possessing unique active surfaces and macro- or nanostructures is addressed herein. For metal-carbon couples, the incorporation of carbon can effectively compensate for the intrinsic deficiency in conductivity of the metallic components. Chemical modification of carbon frameworks, such as nitrogen doping, not only can change the electron-donor character, but also can introduce anchoring sites for immobilizing active metallic centers to form metal-nitrogen-carbon (M-N-C) species, which are thought to facilitate the electrocatalytic process. With thoughtful material design, control over the porosity of composites, the molecular architecture of active metal moieties and macromorphologies of the whole catalysts can be a...

No abstract

great potential to meet our ever-growing demand for energy. These devices appear most promising due to their high energyconversion and storage efficiencies, portability, which can mitigate the intermittent distribution of the aforementioned energy in space and time, and environmental benignancy. [6][7][8][9][10] Fundamentally, these electrochemical systems or devices involve different energy-conversion reactions, such as the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and electrochemical CO 2 reduction (ECR), which provide energy by directly converting chemical energy (e.g., methanol, ethanol, zinc, and hydrogen) into electrical energy, or store energy vice versa. [6][7][8][9][10][11][12] The intrinsically sluggish kinetics of these reactions highlights the critical role of electrocatalysts. In this regard, the development of advanced electrocatalysts has always been the technological bottleneck that hinders the practical applications of these energy techniques at any appreciable scale. [7][8][9][10][11][12] Currently, noble-metal-based materials (e.g., Pt, IrO 2 , RuO 2 , and Au) are considered to be state-of-the-art catalysts for a variety of energy devices, [13][14][15][16] such as proton exchange membrane fuel cells (PEMFCs). [13] In spite of their outstanding catalytic performance for many electrochemical reactions, the high cost and scarcity of these noble metals severely hamper their large-scale commercialization. [17] Further, precious metal catalysts face issues with poisoning when exposed to a range of chemical compounds like methaol and carbon monoxide, leading to significant activity loss. [18] Therefore, extensive studies have focused on the development of alternative electrocatalysts with high activity, long stability, low cost, widespread availability, and facile synthesis. [8][9][10]19,20] To replace precious-metal-based catalysts, a wide range of non-noble-metal materials, especially transition-metal-based materials and metal-free carbon materials, have been intensively investigated as electrocatalysts for different applications. [21] Most of these electrocatalyst candidates show great promise in energy-conversion reactions. Nevertheless, very few alternative materials have yet to achieve superior electrochemical properties to those of noble-metal-based catalysts. Fortunately, the accumulation of experimental and theoretical studies have significantly advanced our knowledge on the chemical and physical nature of various candidate materials. [10][11][12] For example, our group has shed light on the activity origin of The key challenge to developing renewable and clean energy technologies lies in the rational design and synthesis of efficient and earth-abundant catalysts for a wide variety of electrochemical reactions. This review presents materials design strategies for constructing improved electrocatalysts based on MOF precursors/templates, with special emphasis on component manipulation, morphology control, and structure engineering. G...

A core-shell Ru@IrO x heterostructured nanocrystal was designed and constructed to be OER electrocatalyst in acidic media. Enhanced by strong charge redistribution across the core-shell heterojunction, this catalyst not only breaks the activity and stability limits of RuO 2 and IrO 2 simultaneously but also outperforms most of the known acidic OER electrocatalysts. This project offers a new idea to simultaneously enhance electrocatalytic activity and stability by inducing charge redistribution within heterostructured electrocatalysts.

No abstract