An enduring catalyst built from carbon: Splitting water into its constituent elements, hydrogen and oxygen, generally requires the assistance of metal catalysts. Liu et al. now show that a metal-free hybrid material composed of carbon and nitrogen can promote this reaction all on its own, with the help of some visible light. The photocatalyst combines one material (C ₃ N ₄ ) known to split water into hydrogen and peroxide with a second material (CDot) that breaks the peroxide down before it can damage the first. The robust stability of this hybrid bodes well for practical implementation of optimized analogs in solar energy storage schemes. Science , this issue p. 970

Carbon nanodots (C-dots) have generated enormous excitement because of their superiority in water solubility, chemical inertness, low toxicity, ease of functionalization and resistance to photobleaching. In this review, by introducing the synthesis and photo- and electron-properties of C-dots, we hope to provide further insight into their controversial emission origin (particularly the upconverted photoluminescence) and to stimulate further research into their potential applications, especially in photocatalysis, energy conversion, optoelectronics, and sensing.

High quality carbon nanodots (C-dots) with high purity were synthesized through a mild, one-step electrochemical approach, without the assistance of any chemicals but only pure water. This high productivity method makes the synthetic process of C-dots synthesis both economical as well as environment-friendly. The as prepared C-dots are predominantly multi-layer graphene oxide, with luminescence and high up-conversion photoluminescence (emission of light at shorter wavelengths than the excitation wavelength). Meanwhile, C-dots showed peroxidise mimetic function and visible-light-sensitive photocatalytic activity for methyl orange degradation. In addition, a novel photocatalyst (TiO₂/C-dots) was obtained by combining C-dots with TiO₂ through an easy hydrothermal method. Remarkably, TiO₂/C-dots exhibited an excellent visible-light photocatalytic activity.

The hydrogen evolution reaction (HER) based on water electrolysis is a promising strategy for hydrogen energy production, in which the key point is seeking low-cost, high efficiency and stable electrocatalysts. Currently, the most efficient electrocatalysts for the HER are Pt-based catalysts (especially commercial Pt/C), but the low abundance and high cost of Pt hinder their widespread application. Herein, we demonstrate that a cobalt molybdenum phosphide nanocrystal coated by a few-layer N-doped carbon shell (CoMoP@C) is an excellent substitute for the HER. CoMoP@C is prepared by a one-step pyrolysis method on a large scale with polyoxometalate (POM) as a molecular platform. The catalytic activity of CoMoP@C is close to that of commercial 20% Pt/C under pH = 0–1 conditions and superior to that of 20% Pt/C under pH = 2–14 conditions at high overpotential (e.g. η > 240 mV at pH = 2.2). In real seawater, CoMoP@C exhibits stable HER performance with a high Faradaic efficiency (FE) of 92.5%, while the HER activity of 20% Pt/C dramatically decreases after 4 h. The remarkable HER performance of CoMoP@C should be attributed to the low free energy of H on the central CoMoP crystalline core and the multiple functions of the outer N-doped C shell (especially the strong H⁺ absorption behavior). This work may provide new options for the design and preparation of promising HER electrocatalysts superior to Pt/C, which can be used directly in seawater.