Among them, the nitrogen-coordinated transition-metal (TM) single-atoms (SAs) supported on carbon substrates have emerged as a new class of ORR electrocatalysts with enormous potentials. [3-5] These SA electrocatalysts (SAECs) anchor TM-SAs to the carbon substrates via TMnitrogen (TMN x) coordination bonds that also act as the ORR active sites. It has been commonly accepted that the ORR activity of such TMN x-coordinated SA sites can be promoted by optimizing the binding strengths of ORR intermediates (e.g., *O 2 , *OOH, *OH, *O) to the active site via the altering of their electronic structures. [6] Various approaches have been reported to alter the electronic structures of TMN x-coordinated SA sites by modulating N types and coordinating numbers, [7] partially replacing N with other nonmetal elements (e.g., O, S, and P), [8] or the chemical compositions of carbon substrates. [9] Recently, the hetero-SAs (h-SAs) involving two different TMs (e.g., Co/Zn, Fe/Co, Fe/ Zn) have been successfully anchored to the carbon substrates as ORR SAECs. [10] Such an approach takes the advantage of the coexistence of two different TM-SA sites, through the pairing The development of oxygen reduction reaction (ORR) electrocatalysts based on earth-abundant nonprecious materials is critically important for sustainable large-scale applications of fuel cells and metal-air batteries. Herein, a hetero-single-atom (h-SA) ORR electrocatalyst is presented, which has atomically dispersed Fe and Ni coanchored to a microsized nitrogen-doped graphitic carbon support with unique trimodal-porous structure configured by highly ordered macropores interconnected through mesopores. Extended X-ray absorption fine structure spectra confirm that Fe-and Ni-SAs are affixed to the carbon support via FeN 4 and NiN 4 coordination bonds. The resultant Fe/Ni h-SA electrocatalyst exhibits an outstanding ORR activity, outperforming SA electrocatalysts with only Fe-or Ni-SAs, and the benchmark Pt/C. The obtained experimental results indicate that the achieved outstanding ORR performance results from the synergetic enhancement induced by the coexisting FeN 4 and NiN 4 sites, and the superior mass-transfer capability promoted by the trimodal-porous-structured carbon support. The development of oxygen reduction reaction (ORR) electrocatalysts based on earth-abundant nonprecious materials to replace the scarce platinum-group-metal-based ones is critically important for sustainable large-scale commercial applications of fuel cells and metal-air batteries. [1] The extensive research efforts over the recent years have led to a variety of The ORCID identification number(s) for the author(s) of this article can be found under

A flexible air electrode (FAE) with both high oxygen electrocatalytic activity and excellent flexibility is the key to the performance of various flexible devices, such as Zn-air batteries. A facile two-step method, mild acid oxidation followed by air calcination that directly activates commercial carbon cloth (CC) to generate uniform nanoporous and super hydrophilic surface structures with optimized oxygen-rich functional groups and an enhanced surface area, is presented here. Impressively, this two-step activated CC (CC-AC) exhibits superior oxygen electrocatalytic activity and durability, outperforming the oxygen-doped carbon materials reported to date. Especially, CC-AC delivers an oxygen evolution reaction (OER) overpotential of 360 mV at 10 mA cm −2 in 1 m KOH, which is among the best performances of metal-free OER electrocatalysts. The practical application of CC-AC is presented via its use as an FAE in a flexible rechargeable Zn-air battery. The bendable battery achieves a high open circuit voltage of 1.37 V, a remarkable peak power density of 52.3 mW cm −3 at 77.5 mA cm −3 , good cycling performance with a small chargedischarge voltage gap of 0.98 V and high flexibility. This study provides a new approach to the design and construction of high-performance selfsupported metal-free electrodes.

The vast majority of the reported hydrogen evolution reaction (HER) electrocatalysts perform poorly under alkaline conditions due to the sluggish water dissociation kinetics. Herein, a hybridization catalyst construction concept is presented to dramatically enhance the alkaline HER activities of catalysts based on 2D transition metal dichalcogenides (TMDs) (MoS and WS ). A series of ultrathin 2D-hybrids are synthesized via facile controllable growth of 3d metal (Ni, Co, Fe, Mn) hydroxides on the monolayer 2D-TMD nanosheets. The resultant Ni(OH) and Co(OH) hybridized ultrathin MoS and WS nanosheet catalysts exhibit significantly enhanced alkaline HER activity and stability compared to their bare counterparts. The 2D-MoS /Co(OH) hybrid achieves an extremely low overpotential of ≈128 mV at 10 mA cm in 1 m KOH. The combined theoretical and experimental studies confirm that the formation of the heterostructured boundaries by suitable hybridization of the TMD and 3d metal hydroxides is responsible for the improved alkaline HER activities because of the enhanced water dissociation step and lowers the corresponding kinetic energy barrier by the hybridized 3d metal hydroxides.

We presented a new type II heterojunction photocatalyst with a strong built-in electric field aligned between the spatially well-defined redox sites to effectively suppress the charge recombination for efficient photocatalytic hydrogen generation via HI splitting. This brings the hydrogen generation performance of the perovskite-based photocatalysts to a new horizon with a champion STH efficiency of 1.09% and a record hydrogen generation activity of 13.6 mmol g À1 h À1 under visible light.