Cao Na,Chen Zheng,Zang Ketao,Xu Jie,Zhong Jun,Luo Jun,Xu Xin,Zheng Gengfeng
The electrochemical N 2 fixation to produce ammonia is attractive but significantly challenging with low yield and poor selectivity. Herein, we first used density function theory calculations to reveal adjacent bi-Ti 3+ pairs formed on anatase TiO 2 as the most active electrocatalytic centers for efficient N 2 lying-down chemisorption and activation. Then, by doping of anatase TiO 2 with Zr 4+ that has similar d -electron configuration and oxide structure but relatively larger ionic size, the adjacent bi-Ti 3+ sites were induced and enriched via a strained effect, which in turn enhanced the formation of oxygen vacancies. The Zr 4+ -doped anatase TiO 2 exhibited excellent electrocatalytic N 2 fixation performances, with an ammonia production rate (8.90 µg·h −1 ·cm −2 ) and a Faradaic efficiency of 17.3% at −0.45 V versus reversible hydrogen electrode under ambient aqueous conditions. Moreover, our work suggests a viewpoint to understand and apply the same-valance dopants in heterogeneous catalysis, which is generally useful but still poorly understood.
Chunran Zhao,Chenrui Wang,Xujie Ren,Shude Yuan,Leihong Zhao,Lvchao Zhuang,Botao Teng,Ying Wu,Yiming He
Fabricating heterophase junctions proves to be an efficient strategy for achieving efficient charge separation and enhancing the catalytic activity of photocatalysts. Surprisingly, this approach is rarely utilized in the field of piezocatalysis. In this work, a novel ZnSnO 3 heterophase junction catalyst was fabricated by combining rhombohedral (R-ZnSnO 3 ) and orthorhombic (O-ZnSnO 3 ) phases for efficient piezo and piezo-photocatalytic RhB degradation and N 2 fixation. The piezocatalytic RhB degradation rates of ZnSnO 3 heterophase catalysts are 5.6 and 3.6 times higher than those of O-ZnSnO 3 and R-ZnSnO 3 , respectively, with similar enhancements observed in piezocatalytic N 2 fixation. The coupling of R-ZnSnO 3 and O-ZnSnO 3 does not increase the piezoelectric properties; however, an S-scheme structure formed at the interface. Under the combined effects of band bending, interface electric fields, and Coulomb attraction, electrons and holes migrate and achieve effective spatial separation. This result supports the energy band theory over the induction charge theory, contributing to the ongoing debate in piezocatalytic mechanisms. Electrochemical analyses and piezo-photocatalytic tests further indicate that ZnSnO 3 heterophase junctions exhibit a synergistic effect between piezocatalysis and photocatalysis. This synergy can be attributed to the complementary effects of photoinduced carrier generation and piezoelectric field-assisted carrier separation. Hydroxyl radicals, superoxide radicals, and holes serve as the primary active species responsible for piezocatalytic RhB degradation through a mechanism similar to photocatalysis. Theoretical calculations reveal that the Sn site on the surface of O-ZnSnO 3 acts as the active site within the ZnSnO 3 heterophase junction, providing valuable insights for future catalyst development. This work offers a deeper understanding of the synergistic mechanisms in piezo-photocatalysis, presenting a promising route for efficient environmental and energy applications.
Diazotrophic cyanobacteria can fix nitrogen gas (N 2 ) but are usually scarce in nitrogen-limited coastal waters, which poses an apparent ecological paradox. One hypothesis is that high salinities (> 10 g/L NaCl) may inhibit cyanobacterial N 2 fixation. However, here we show that N 2 fixation in a unicellular coastal cyanobacterium exclusively depends on sodium ions and is inhibited at low NaCl concentrations (< 4 g/L). In the absence of Na + , cells of Cyanothece sp. ATCC 51142 (recently reclassified as Crocosphaera subtropica ) upregulate the expression of nifHDK genes and synthesise a higher amount of nitrogenase, but do not fix N 2 and do not grow. We find that the loss of N 2 -fixing ability in the absence of Na + is due to insufficient ATP supply. Additional experiments suggest that N 2 fixation in this organism is driven by sodium energetics and mixed-acid fermentation, rather than proton energetics and aerobic respiration, even though cells were cultured aerobically. Further work is needed to clarify the underlying mechanisms and whether our findings are relevant to other coastal cyanobacteria.
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