© 2020, The Author(s), under exclusive licence to Springer Nature Limited. The use of nitrogen fertilizers has been estimated to have supported 27% of the world's population over the past century. Urea (CO(NH2)2) is conventionally synthesized through two consecutive industrial processes, N2 + H2 → NH3 followed by NH3 + CO2 → urea. Both reactions operate under harsh conditions and consume more than 2% of the world's energy. Urea synthesis consumes approximately 80% of the NH3 produced globally. Here we directly coupled N2 and CO2 in H2O to produce urea under ambient conditions. The process was carried out using an electrocatalyst consisting of PdCu alloy nanoparticles on TiO2 nanosheets. This coupling reaction occurs through the formation of C-N bonds via the thermodynamically spontaneous reaction between *N=N* and CO. Products were identified and quantified using isotope labelling and the mechanism investigated using isotope-labelled operando synchrotron-radiation Fourier transform infrared spectroscopy. A high rate of urea formation of 3.36 mmol g-1 h-1 and corresponding Faradic efficiency of 8.92% were measured at-0.4 V versus reversible hydrogen electrode.

Electrochemically reversible redox couples that embrace more electron transfer at a higher potential are the eternal target for energy storage batteries. Here, we report a four-electron aqueous zinc-iodine battery by activating the highly reversible I2/I+ couple (1.83 V vs. Zn/Zn2+) in addition to the typical I−/I2 couple (1.29 V). This is achieved by intensive solvation of the aqueous electrolyte to yield ICl inter-halogens and to suspend its hydrolysis. Experimental characterization and modelling reveal that limited water activity and sufficient free chloride ions in the electrolyte are crucial for the four-electron process. The merits of the electrolyte also afford to stabilize Zn anode, leading to a reliable Zn-I2 aqueous battery of 6000 cycles. Owing to high operational voltage and capacity, energy density up to 750 Wh kg−1 based on iodine mass was achieved (15–20 wt% iodine in electrode). It pushes the Zn-I2 battery to a superior level among these available aqueous batteries.

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Topological phononic states, facilitating acoustic unique transports immunizing to defects and disorders, have significantly revolutionized our scientific cognition of acoustic wave systems. Up to now, the theoretical and experimental demonstrations of topologically protected one-way transports with pseudospin states in a phononic crystal beyond the graphene lattice with C 6v symmetry are still unexploited. Furthermore, the tunable topological states, in form of robust reconfigurable acoustic pathways, have been evaded in the topological phononic insulators. Here, we realize a topological phase transition in the double Dirac degenerate cone of rotatable triangular phononic crystals with C 3v symmetry, by introducing the zone folding mechanism. Along a topological domain wall between two portions of phononic crystals with distinct topological phases, we experimentally observe the quantum spin Hall (QSH) effect for xiabz2013@hnu.edu.cn (Baizhan Xia) djyu@hnu.edu.cn (Dejie Yu) liujian@hnu.edu.cn (Jian Liu)

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