Perovskite solar cells (PSCs) have reached an impressive efficiency over 23%. One of its promising characteristics is the low-cost solution printability, especially for flexible solar cells. However, printing large area uniform electron transport layers on rough and soft plastic substrates without hysteresis is still a great challenge. Herein, we demonstrate slot-die printed high quality tin oxide films for high efficiency flexible PSCs. The inherent hysteresis induced by the tin oxide layer is suppressed using a universal potassium interfacial passivation strategy regardless of fabricating methods. Results show that the potassium cations, not the anions, facilitate the growth of perovskite grains, passivate the interface, and contribute to the enhanced efficiency and stability. The small size flexible PSCs achieve a high efficiency of 17.18% and large size (5 × 6 cm2) flexible modules obtain an efficiency over 15%. This passivation strategy has shown great promise for pursuing high performance large area flexible PSCs.

Single-atom catalysts (SACs) are the smallest entities for catalytic reactions with projected high atomic efficiency, superior activity, and selectivity; however, practical applications of SACs suffer from a very low metal loading of 1-2 wt%. Here, a class of SACs based on atomically dispersed transition metals on nitrogen-doped carbon nanotubes (MSA-N-CNTs, where M = Ni, Co, NiCo, CoFe, and NiPt) is synthesized with an extraordinarily high metal loading, e.g., 20 wt% in the case of NiSA-N-CNTs, using a new multistep pyrolysis process. Among these materials, NiSA-N-CNTs show an excellent selectivity and activity for the electrochemical reduction of CO to CO, achieving a turnover frequency (TOF) of 11.7 s at -0.55 V (vs reversible hydrogen electrode (RHE)), two orders of magnitude higher than Ni nanoparticles supported on CNTs.

Electrocatalytic water splitting is one of the sustainable and promising strategies to generate hydrogen fuel but still remains a great challenge because of the sluggish anodic oxygen evolution reaction (OER). A very effective approach to dramatically decrease the input cell voltage of water electrolysis is to replace the anodic OER with hydrazine oxidation reaction (HzOR) due to its lower thermodynamic oxidation potential. Therefore, developing the low-cost and efficient HzOR catalysts, coupled with the cathodic hydrogen evolution reaction (HER) is tremendously important for energysaving electrolytic hydrogen production. Herein, a new-type copper-nickel nitride (Cu 1 Ni 2 -N) with rich Cu 4 N/Ni 3 N interface is rationally constructed on the carbon fiber cloth. The three-dimensional electrode exhibits extraordinary HER performance with an overpotential of 71.4 mV at 10 mA cm -2 in 1.0 M KOH, simultaneously delivering an ultralow potential of 0.5 mV at 10 mA cm -2 for HzOR in 1.0 M KOH/0.5 M hydrazine electrolyte. Moreover, the electrolytic cell utilizing the synthesized Cu 1 Ni 2 -N electrode as both the cathode and anode displays a cell voltage of 0.24 V at 10 mA cm -2 with an excellent stability over 75 h. The present work develops the promising copper-nickel-based nitride as a bifunctional electrocatalyst through hydrazine-assistance for energy-saving electrolytic hydrogen production.