The electrochemical reduction of CO2 (CO2RR) to produce valuable synthetic fuel like CH3OH not only mitigates the accumulated greenhouse gas from the environment but is also a promising direction toward attenuating our continuous reliance on fossil fuels. However, CO2RR to yield CH3OH suffers because of large overpotential, competitive H2 evolution reaction (HER), and poor product selectivity. In this regard, intermetallic alloy catalysts open up a wide possibility of fine-tuning the electronic property and attain appropriate structures that facilitate selective CO2RR. Here, we report for the first time the CO2RR over carbon-supported PtZn nano-alloys and probed the crucial role of structures and interfaces as active sites. PtZn/C, Pt3Zn/C, and Pt x Zn/C (1 < x < 3) synthesized from the metal–organic framework material were characterized structurally and morphologically. The catalysts demonstrated structure dependency toward CH3OH selectivity, as the mixed-phase Pt x Zn/C outperformed the phase-pure PtZn/C and Pt3Zn/C. The structure-dependent reaction mechanism and the kinetics were elucidated over the synthesized catalysts with the help of detail experiments and associated density functional theory calculations. Results showed that in spite of low electrochemically active surface area, Pt x Zn could not only have facilitated the single electron transfer to adsorbed CO2 but also showed better binding of the intermediate CO2 •– over its surface. Moreover, the lower bond energy between the mixed-phase surface and −OCH3 compared to the phase-pure catalysts has enabled higher CH3OH selectivity over Pt x Zn. This work opens a wide possibility of studying the role of interfaces between phase-pure nano-alloys toward CO2RR.

Substitution of aliovalent N(3-) and F(-) anions in place of O(2-) in ZnO brings about major changes in the electronic structure and properties, the composition, even with 10 atomic percent or less of the two anions, rendering the material yellow colored with a much smaller band gap. We have examined the variation of band gap of ZnO with progressive substitution of N and F and more importantly prepared Zn2NF which is the composition one obtains ultimately upon complete replacement of O(2-) ions. In this article, we present the results of a first complete study of the crystal and electronic structures as well as of properties of a stable metal nitride fluoride, Zn2NF. This material occurs in two crystal forms, tetragonal and orthorhombic, both with a band gap much smaller than that of ZnO. Electronic structures of Zn2NF as well as ZnO0.2N0.5F0.3 investigated by first-principles calculations show that the valence bands of these are dominated by the N (2p) states lying at the top. Interestingly, the latter is a p-type material, a property that has been anticipated for long time. The calculations predict conduction and valence band edges in Zn2NF to be favorable for water splitting. Zn2NF does indeed exhibit good visible-light-induced hydrogen evolution activity unlike ZnO. The present study demonstrates how aliovalent anion substitution can be employed for tuning band gaps of materials.

Thermoelectric (TE) materials are promising in the context of renewable power generation as they can directly convert waste heat into electricity. Although PbTe is the best known TE material, its use is not encouraged due to concerns of environmental toxicity of lead. A combination of modified self-propagating hightemperature synthesis (SHS) and field-assisted sintering technique (FAST) is employed for the very first time to synthesize a solid solution of PbTe and SnTe. We show that doping of Pb 0.6 Sn 0.4 Te with Mg breaks crystal mirror symmetry and opens up band gap. This results in suppression of bipolar diffusion. Also the increase in degeneracy of valence sub-bands improves Seebeck coefficient. Both these synergistically leads to remarkable enhancement in figure of merit ZT (∼2 at 840 K) and ZT avg (∼1.2 between 500 and 840 K) rendering it into highperformance thermoelectric material by successfully engineering electronic structure. Most importantly, the ZT here is comparable to that of Mg-doped PbTe but has lesser lead content and hence is more environment friendly. The most probable configuration of Pb 0.6 Sn 0.4 Te was also determined for the very first time using site occupancy disorder (SOD) technique.

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A novel, highly efficient composite electrode containing earth-abundant elements (Co–Ni) and graphene has been developed for the electrocatalytic hydrogen evolution reaction in an alkaline medium.