Electrochemical reduction of nitrate to ammonia (nitrate reduction reaction, NO3-RR) under ambient conditions, which overcomes the drawbacks of energy-intensive Haber−Bosch reaction and low-efficient N2 electroreduction, is one of the alternatives...

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In this study, low-crystalline CoOOH nanosheet arrays that are grown on carbon fiber cloth (LC-CoOOH NAs/CFC) were prepared using a facile electrochemical strategy for the oxygen evolution reaction (OER). The lowcrystalline CoOOH nanosheets were assembled randomly by numerous short-range (1−5 nm) ordered grains with different orientations, inducing abundant grain boundaries (edge sites of CoOOH). Moreover, a certain number of structural defects (oxygen vacancies) were also engineered on the low-crystalline CoOOH nanosheets. Benefiting from these abundant edge sites of CoOOH and oxygen vacancies, LC-CoOOH NAs/CFC exhibit much improved OER activity compared to the high-crystallinity CoOOH NAs/CFC with a perfect structure. This research provides a new way to synthesize the defective materials with a short-range ordered structure and lays a valuable theoretical foundation for the structure and property of OER catalysts.

Reaction of transition metal formate M(HCOO)(2).2H2O (M = Mn, Co, Ni) with 4,4'-bpy (4,4-bipyridine) has led to four new compounds with the formula M(HCOO)2(4,4'-bpy).nH2O (M = Mn, Co (1.Mn, 2.Co), n = 0; M = Co, Ni (3.Co, 4.Ni), n = 5). Compounds 1.Mn and 2.Co are isomorphous and crystallized in the tetragonal crystal system with the chiral space group P4(1)2(1)2. They are of three-dimensional diamondoid structure connected by anti-anti formate with 4,4'-bpy in the cavities of the framework reinforcing the intermetallic connections; the diamond-like net was observed also in their azide analogue (Mn(N3)2(4,4'-bpy)). Compounds 3.Co and 4.Ni are isomorphous also but crystallized in the monoclinic crystal system with the space group Cc. Both structures are uninterpenetrated 3D "CdSO4" type with big channels, constructed by anti-anti formate and 4,4'-bpy. This type of net was not observed in their azide analogue. Residing in the channels, water molecules form a new type of 1D tape constructed by vertex-sharing cyclic pentamers. Magnetic measurements were performed on all of these four compounds. 1.Mn and 2.Co are weak ferromagnets with the critical temperature Tc = 5.3 and 7.4 K, respectively. 3.Co is an antiferromagnet with Neel temperature TN = 3.0 K, and 4.Ni is a weak ferromagnet below 20 K. Hysteresis loop can be observed for 2.Co and 4.Ni at 1.8 K. As an analogue of azide, formate can be used to construct molecular architectures, which structurally and magnetically have great similarities to and also differences from those of azide. This offers a promising method for the design of new molecular architectures with formate.