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Developing high-efficiency, inexpensive, and steady non-precious metal oxygen reduction reaction (ORR) catalysts to displace Pt-based catalysts is significant for commercial applications of Al-air battery. Here, we have prepared the Cu/Cu2O-NC catalyst with excellent ORR performance and high stability, due to the synergistic effect of Cu and Cu2O nanoparticles. The half-wave potential (0.8 V) and the limiting-current density (5.20 mA/cm2) of the Cu/Cu2O-NC are very close to those of the 20% Pt/C catalyst (0.82 V, 5.10 mA/cm2). Besides, it exhibits excellent performance with a maximal power density of 250 mW/cm2 and a stable continuous discharge for more than 90 h in the Al-air battery test. The promoting effects of Cu2O towards Cu-based ORR catalysts are illustrated as follows: (i) Cu2O is the major ORR active site by the redox of Cu(II)/Cu(I), which provides excellent ORR activities; (ii) Cu can stabilize the location of Cu2O by assisting the electron transfer to Cu(II)/Cu(I) redox, which is conducive to the high stability of the catalyst. This work provides a useful strategy for enhancing the ORR performance of Cu-based catalysts.

Metal oxides with surface protonation exhibit versatile physical and chemical properties suitable for use in many fields. Here, we develop an electrochemical route to directly protonize the physically assembled oxide particles, such as TiO2, Nb2O5, and WO3, in a Na2SO4 neutral electrolyte, which is a result of electrochemically induced oxygen vacancies reacting with water molecules. With no need of electric connection among particles or between particles and conductive substrate, the electrochemical protonation follows a bottom-up particle-by-particle surface protonation mechanism due to the fact that the protonation inducing high surface conductivity creates an efficient electron transfer pathway among particles. Our results show that electrochemical protonation of particles provides a chance to finely functionalize the surface of a single particle by only adjusting electrode potentials. Such a facile, cost-efficient, and green route is easy to run for a large-scale production and unlocks the potential of semiconductor oxides for various applications.

The photoelectrochemical (PEC) water splitting determines by the light absorption and charge extraction/injection. Here, we dispersedly modified the core-shell structured Ni@Niy Fe1-y (OH)2 on Si photoanodes and in-situ electrochemically converted it to Ni@Niy Fe1-y OOH to form a Si/SiOx /Ni@Niy Fe1-y OOH assembly, exhibiting the adjustable band bending and catalytic ability in water oxidation depending closely on the composition of Niy Fe1-y OOH. Combining with the island-like dispersed distribution to maximize the light absorption and the Ni@Niy Fe1-y shell as a high work function and a catalytic layer to simultaneously enlarge charge extraction and injection, the Si/SiOx /Ni@Ni0.7 Fe0.3 OOH assembly achieved an onset potential of 1.0 VRHE , a saturated current density of 35.4 mA cm-2 and a more than 50 h stability in an electrolyte with pH 9 under AM1.5G simulated sunlight irradiation. Our findings suggested that regulating the charge energetics at Si-electrolyte interface by discontinuously modifying a composition-adjustable core-shell structure is a potential route to develop highly efficient PEC devices.

For heterojunction semiconductor photoelectrodes, efficient charge separation is localized in the junction-induced electric field region and charge transfer follows a band-to-band charge-transfer pathway. Here, we found that polaron states at the heterojunction interface have a function of storing and transferring electrons. As a successful demonstration, we verified that the polaron states (Ti3+OH) on TiO2 are not passivated when used to create a CdS/TiO2 heterojunction and function as an efficient pathway for massively capturing, storing, and transferring the electrons from conduction bands of both TiO2 and CdS, thus effectively enhancing the charge separation efficiency of the heterojunction photoanode. The electron throughput of polaron states remains a positive correlation with polaron state density. Interfacial electron transfer through the TiO2 surface polaron states has great potential application in the development of high-performance heterojunction devices based on TiO2.

To break challenges in creating frustrated Lewis pairs (FLPs) on highly stable inorganic materials, an ordering FLPs route is proposed by irradiation of dual-metal hydroxide with alternating light-stable and light-unstable terminal hydroxyls on dual-metal hydroxide. As a successful example, a single-crystal ZnSn(OH)6 cube with a (100) surface of alternating Zn−OH and Sn−OH terminal hydroxyl groups is irradiated under 300 W Xe lamp to create oxygen vacancies (OVs, Lewis acid) via holes oxidizing light-unstable terminal hydroxyls at Sn sites. The FLPs are accordingly constructed between the photo-induced OVs and its proximal light-stable Zn−OH terminal hydroxyls (Lewis base), significantly contributing to the decreased barriers during capture, activation, and reduction of CO2 into CO with the assistance of H2. The present findings are a big leap for designing highly stable FLPs-based inorganic solid catalysts.

Aluminum-air (Al-air) battery has been regarded as one of the most promising next-generation energy storage devices. Manganese oxides (MnOx) are widely studied as non-noble metal oxygen reduction reaction (ORR) electrocatalysts with low cost and high stability. However, they still possess inferior ORR activity for commercial applications. In this study, an architecture of CeO2 nanoparticles decorated MnOOH nanorods (MnOOH@CeO2) is prepared by a simple one-step solvothermal method as an ORR catalyst. Interestingly, the incorporation of CeO2 can significantly strengthen the ORR activities of MnOOH. The half-wave potential of MnOOH@CeO2 reaches 0.80 V vs. RHE, which shows a 30 mV positive shift compared with MnOOH. It has been verified that the significant improvement ORR activity of MnOOH@CeO2 is attributed to their synergistic effect of MnOOH and CeO2, resulting in much better oxygen activation, oxygen enrichment, and H2O2 inhibition. In a practical double-face flow Al-air battery system, MnOOH@CeO2 catalyst even exhibits better electrocatalytic performance (the discharge voltage of 0.65 V at 400 mA cm−2, the higher energy density of 3595.4 Wh kgAl−1 and power density of 302.8 mW cm−2) than the commercial 20% Pt/C, further highlighting the multi-functions of CeO2 nanoparticles attaches to MnOOH nanorods.