Deeply Rechargeable and Hydrogen-Evolution-Suppressing Zinc Anode in Alkaline Aqueous Electrolyte.

Metallic zinc as a rechargeable anode material for aqueous batteries has gained tremendous attention. Zn-air batteries, which operate in alkaline electrolytes, are promising with the highest theoretical volumetric energy density. However, rechargeable zinc anodes develop slowly in alkaline electrolytes due to passivation, dissolution, and hydrogen evolution issues. In this study, we report the design of a submicron zinc anode sealed with an ion-sieving coating that suppresses hydrogen evolution reaction. The design is demonstrated with ZnO nanorods coated by TiO2, which overcomes passivation, dissolution, and hydrogen evolution issues simultaneously. It achieves superior reversible deep cycling performance with a high discharge capacity of 616 mAh/g and Coulombic efficiency of 93.5% when cycled with 100% depth of discharge at lean electrolyte. It can also deeply cycle ∼350 times in a beaker cell. The design principle of this work may potentially be applied to other battery electrode materials.

Detrimental effects of SO2 on gaseous mercury(II) adsorption and retention by CaO-based sorbent traps: Competition and heterogeneous reduction.

Reliable gaseous Hg(II) measurement is crucial to mercury emissions control from coal-fired flue gas, but Hg(II) sampling under SO2 condition could probably increase the uncertainty of sorbent traps. CaO-AcS synthesized from calcium acetate and porous support were previously demonstrated to be effective for Hg(II) trapping under SO2-free condition. This work further evaluated SO2 influence on its Hg(II) retention ability via integrating experimental and DFT computational studies. Increased breakthrough rate of HgCl2 was found in a two-section CaO-AcS trap under SO2 conditions. Significant basicity and porosity loss of CaO-AcS were attributed to the formation of agglomerate CaSO3. Hg0 release from CaO-AcS samples suggested potential reactions between Hg(II) and SO2. The detected HgO and Hg2SO4 species by Hg-TPD in CaO-AcS further confirmed this speculation. Moreover, both competition and reduction effects of SO2 on surface-bound Hg(II) species were substantiated by DFT calculations. SO2 showed a stronger interaction with CaO than HgCl2 because SO2 has a lower LUMO level and can accept electrons easier. Reaction pathways indicated Hg(II) was partially reduced to Hg2SO4 under SO2-deficient condition, or directly reduced to Hg0 under SO2-rich condition. This work fully proposed the SO2 influence mechanisms and improvement countermeasures for practical gaseous Hg(II) sampling.