Developing highly efficient catalysts for oxygen evolution reactions (OER) is a key step for rechargeable metal− oxygen batteries and water splitting. Usually, binary NiFe or ternary NiCoFe nano-alloys are used as the OER catalysts. Herein, combining the precursor alloy design with chemical etching, a simple dealloying route is developed to controllably incorporate five or more nonprecious metals into one nanostructured alloy with a naturally oxidized surface, that is, nanoporous high entropy alloys (np-HEAs) covered with high-entropy (oxy)hydroxides (HEOs). It is found that the alloy composition plays a dominant role in the OER activity enhancement with the np-AlNiCoFeX (X = Mo, Nb, Cr) combination showing the highest activity. Forming quinary HEAs also greatly enhances the electrochemical cycling stabilities compared with the ternary and quaternary counterparts. The result indicates the significance of synergistically incorporating five or more metal elements in one single-phase nanostructure, which provides more structural and chemical degrees of freedom to boost the catalytic performance, overcoming the restriction of normal binary or ternary alloys. Multinary transition metal-based np-HEA is a new class of promising catalyst for various important reactions.

Developing bifunctional electrocatalysts with high activities and long durability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial toward the practical implementation of rechargeable metal–air batteries. Here, a 3D nanoporous graphene (np‐graphene) doped with both N and Ni single atoms/clusters is reported. The predoping of N by chemical vapor deposition (CVD) dramatically increases the Ni doping amount and stability. The resulting N and Ni codoped np‐graphene has excellent electrocatalytic activities for both the ORR and the OER in alkaline aqueous solutions. The synergetic effects of N and Ni dopants are revealed by density functional theory calculations. The free‐standing Ni,N codoped 3D np‐graphene shows great potential as an economical catalyst/electrode for metal–air batteries.

Heteronuclear double-atom catalysts, unlike single atom catalysts, may change the charge density of active metal sites by introducing another metal single atom, thereby modifying the adsorption energies of reaction intermediates and increasing the catalytic activities. First, density functional theory calculations are used to figure out the best combination by modeling two transition-metal atoms from Fe, Co, and Ni onto N-doped graphene. Generally, Fe and Co sites are highly active for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), respectively. The combination of Co and Fe to form CoFe–N–C not only further improves the Fe’s ORR and Co’s OER activities but also greatly enhances the Co site’s ORR and Fe site’s OER activities. Then, we synthesize the CoFe–N–C by a two-step pyrolysis process and find that the CoFe–N–C exhibits exceptional ORR and OER electrocatalytic activities in alkaline media, significantly superior to Fe–N–C and Co–N–C and even commercial catalysts.

Single‐atom cobalt‐based CoNC are promising low‐cost electrocatalysts for oxygen reduction reaction (ORR). However, further increasing the single cobalt‐based active sites and the ORR activity remain a major challenge. Herein, an acetate (OAc) assisted metal–organic framework (MOF) structure‐engineering strategy is developed to synthesize hierarchical accordion‐like MOF with higher loading amount and better spatial isolation of Co and much higher yield when compared with widely reported polyhedron MOF. After pyrolysis, the accordion‐structured CoNC (CoNC (A)) is loaded with denser CoN4 active sites (Co: 2.88 wt%), approximately twice that of Co in the CoNC reported. The presence of OAc in MOF also induces the generation of big pores (5–50 nm) for improving the accessibility of active sites and mass transfer during catalytic reactions. Consequently, the CoNC (A) catalyst shows an admirable ORR activity with a E1/2 of 0.89 V (40 mV better than Pt/C) in alkaline electrolytes, outstanding durability, and absolute tolerance to methanol in both alkaline and acidic media. The CoNC‐based Zn‐air battery exhibits a high specific capacity (976 mAh g−1Zn), power density (158 mW cm−2), rate capability, and long‐term stability. This work demonstrates a reliable approach to construct single atom doped carbon catalysts with denser accessible active sites through MOF structure engineering.

BackgroundA major constraint affecting the quality and productivity of chrysanthemum is the unusual period of low temperature occurring during early spring, late autumn, and winter. Yet, there has been no systematic investigation on the genes underlying the response to low temperature in chrysanthemum. Herein, we used RNA-Seq platform to characterize the transcriptomic response to low temperature by comparing different transcriptome of Chrysanthemum nankingense plants and subjecting them to a period of sub-zero temperature, with or without a prior low temperature acclimation.ResultsSix separate RNA-Seq libraries were generated from the RNA samples of leaves and stems from six different temperature treatments, including one cold acclimation (CA), two freezing treatments without prior CA, two freezing treatments with prior CA and the control. At least seven million clean reads were obtained from each library. Over 77% of the reads could be mapped to sets of C. nankingense unigenes established previously. The differentially transcribed genes (DTGs) were identified as low temperature sensing and signalling genes, transcription factors, functional proteins associated with the abiotic response, and low temperature-responsive genes involved in post-transcriptional regulation. The differential transcription of 15 DTGs was validated using quantitative RT-PCR.ConclusionsThe large number of DTGs identified in this study, confirmed the complexity of the regulatory machinery involved in the processes of low temperature acclimation and low temperature/freezing tolerance.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-844) contains supplementary material, which is available to authorized users.