To achieve the energy‐effective ammonia (NH3) production via the ambient‐condition electrochemical N2 reduction reaction (NRR), it is vital to ingeniously design an efficient electrocatalyst assembling the features of abundant surface deficiency, good dispersibility, high conductivity, and large surface specific area (SSA) via a simple way. Inspired by the fact that the MXene contains thermodynamically metastable marginal transition metal atoms, the oxygen‐vacancy‐rich TiO2 nanoparticles (NPs) in situ grown on the Ti3C2Tx nanosheets (TiO2/Ti3C2Tx) are prepared via a one‐step ethanol‐thermal treatment of the Ti3C2Tx MXene. The oxygen vacancies act as the main active sites for the NH3 synthesis. The highly conductive interior untreated Ti3C2Tx nanosheets could not only facilitate the electron transport but also avoid the self‐aggregation of the TiO2 NPs. Meanwhile, the TiO2 NPs generation could enhance the SSA of the Ti3C2Tx in return. Accordingly, the as‐prepared electrocatalyst exhibits an NH3 yield of 32.17 µg h−1 mg−1cat. at −0.55 V versus reversible hydrogen electrode (RHE) and a remarkable Faradaic efficiency of 16.07% at −0.45 V versus RHE in 0.1 m HCl, placing it as one of the most promising NRR electrocatalysts. Moreover, the density functional theory calculations confirm the lowest NRR energy barrier (0.40 eV) of TiO2 (101)/Ti3C2Tx compared with Ti3C2Tx or TiO2 (101) alone.

Ammonia (NH 3 ) is essential to human life due to its vital roles in fuel production, agricultural cultivation and industrial manufacture. [1,2] The abundant nitrogen (N 2 ) in the earth's atmosphere is the main raw material for the synthesis of NH 3 , [3] but the large bond energy (940.95 kJ mol −1 ) of NN bond [1,4] makes N 2 reduction reaction (NRR) extremely difficult. [5] At present, the traditionally industrial NH 3 synthesis strongly relies on the Haber-Bosch process, which has to be conducted at high pressures at 200-300 atm and high temperature of ≈500 °C. [6] Furthermore, such production method is energy-intensive that consumes 1-3% of the global energy annually and emit tons of CO 2 correspondingly. [7] Over the last decades, electrochemical NRR has attracted global attention due to its renewable raw materials of N 2 and water as well as ambient synthesis condition. [8] With recent booming development, the study of NRR electrocatalysts has moved from precious metals to cheap and abundant transition metal oxides and metal-free materials, etc. [9] However, due to the lack of rational and target-specific design of the NRR electrocatalyst, it is still a difficult task to reach an ideal electrocatalyst fulfilling with the requirements of high NH 3 yield, excellent selectivity and cost-effectiveness simultaneously. To meet these requirements, it is expected that catalysts contain abundant active sites. [10] Under this context, various low-dimensional catalysts have been extensively investigated, such as 2D nanosheets and 0D quantum dots (QDs) due to their ultrahigh ratio of active sites and defects exposed on the surfaces.QDs, especially derived from 2D materials (2D-QDs), are often with small size of less than 10 nm, enhanced surface defects and large surface specific area, thus offering abundantactive basal and edge sites, together with various functional groups. [8,11,12] As a result, a large space has been generated for advanced rational design for N 2 adsorption and full reduction. [13,17] So far, however, the effect of edge sites and their functional groups on NRR performance of 2D-QDs is poorly known. MXene, an emerging typical 2D material, can be expressed by the chemical formula of M n+1 X n T x (n = 1, 2 and 3), [18,20] where M stands for the transition metal (e.g., Ti, Ta, Nb, V, Mo), the X represents the nitrogen or carbon or carbonitride, while T x represents a large number of surface functional groups (e.g., OH, F). [21,22] Due to the excellent conductivity and stability, To enable an efficient and cost-effective electrocatalytic N 2 reduction reaction (NRR) the development of an electrocatalyst with a high NH 3 yield and good selectivity is required. In this work, Ti 3 C 2 T x MXene-derived quantum dots (Ti 3 C 2 T x QDs) with abundant active sites enable the development of efficient NRR electrocatalysts. Given surface functional groups play a key role on the electrocatalytic performance, density functional theory calculations are first conducted, clarifying that hydroxyl groups on Ti 3 C 2...

Artificial photocatalysis offers a clean approach for producing H2O2. However, the poor selectivity and activity of H2O2 production hamper traditional industrial applications and emerging photodynamic therapy (PDT)/chemodynamic therapy (CDT). Here, we report a well-defined C5N2 photocatalyst with a conjugated C=N linkage for highly selective and efficient non-sacrificial H2O2 production both in normoxic and hypoxic systems. The strengthened delocalization of −electrons by linkers in C5N2 significantly downshifted the band position, which eliminated the side photoreduction reaction of H2 evolution in thermodynamics and promoted water oxidation ability in kinetics. As a result, C5N2 had a competitive overall H2O2 production with solar-tochemical conversion efficiency of 0.55% and more interestingly, exhibited the highest activity so far in hypoxic condition (698 M/h). C5N2 was further applied to hypoxic PDT/CDT, exhibiting outstanding performance in conspicuous cancer cell death and synchronous bioimaging. It shed light on unlocking linker functions in electronic structure engineering of carbon nitrides for highly efficient overall photosynthesis of H2O2 and expanded the scope of their prospective application in health care.

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