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Abstract The Bi-modified MnO2 cathode is an enabling technology for rechargeable alkaline Zn batteries, which are under intense study for low-cost, sustainable, non-flammable grid-scale energy storage. Although the effect of Bi on MnO2 rechargeability has been known for decades, its mechanism has remained a longstanding challenge in the field. Here, we detail an oxidative electrochemical coupling between Bi and Mn in electrodes of commercially relevant areal capacity (12 mAh/cm2). Specifically, operando X-ray absorption spectroscopy and differential capacity analysis reveal that electrochemical capacity associated with Bi oxidation is shifted up into a voltage range where only Mn oxidation is expected. This oxidative coupling occurs precisely when failure by Mn3O4 formation is known to occur in the absence of Bi, and coincides with the potential range at which the β′-MnOOH intermediate exists during charge. The stabilization of β′-MnOOH by Bi-Mn coupling reveals its critical role in rechargeability, as this intermediate is the primary material source of Mn3O4 in unmodified electrodes. Only a small fraction of the total Bi capacity, corresponding to approximately 2 wt % Bi2O3, participates in this coupling, and it is demonstrated that the overall extent of rechargeability is controlled by the diffusion of dissolved Bi ions through the microporous structure of the MnO2 active material. Consistent with this transport-limited scenario, structurally incorporating Bi3+ directly into the MnO2 lattice is shown to be counterproductive, as it pillars the structure and impedes the electrochemical conversion it was intended to assist. 

Electrochemical processes that utilize biomass-derived ethanol as a source of electrons and protons offer a sustainable energy strategy, yet their practical implementation is limited by sluggish ethanol oxidation reaction (EOR) kinetics and catalyst poisoning. Here, we report a modular multi-interface nanocrystal catalyst comprising core/shell Co 2 P/Pd and Pd-Au heterostructured interfaces that exhibit complementary functions for the enhanced EOR catalysis. The Co 2 P/Pd interface boosts Pd atom utilization and lowers the kinetic barriers for ethanol-to-acetate conversion, while the Pd-Au interface effectively alleviates CO poisoning caused by C–C bond cleavage of ethanol. In-depth analyses using in situ attenuated total reflectance-surface-enhanced infrared absorption spectroscopy, differential electrochemical mass spectrometry, and density functional theory calculations elucidate the mechanistic roles of these interfaces. The optimized Co 2 P/Pd-Au 0.08 nanorods achieve an excellent mass activity, underscoring the potential of modular, multi-interface nanocrystals for advancing EOR catalysis and offering a generalizable strategy for broader catalytic innovations. 

Understanding oxide reduction is critical for advancing metal production, catalysis and energy technologies. Although carbon monoxide (CO) and hydrogen (H2) are widely used reductants, the mechanisms by which they work are often presumed to be similar, both involving lattice oxygen removal. However, because of growing interest in replacing CO with H2 to lower CO2 emissions, distinguishing gas-specific reduction pathways is critical. Yet, capturing these atomic-scale processes under reactive gas and high-temperature conditions remains challenging. Here we use environmental transmission electron microscopy, which is capable of real-time, atomic-resolution imaging of gas–solid redox reactions10,11,12,13,14,15,16, to directly visualize the gas-dependent oxide reduction dynamics in NiO. We show that CO drives surface nucleation and the growth of metallic Ni islands, leading to self-limiting surface metallization. Conversely, H2 activates a coupled surface-to-bulk transformation, where protons from dissociated H2 infiltrate the oxide lattice to promote the inward migration of surface-generated oxygen vacancies and enabling bulk metallization. By contrast, oxygen vacancies formed by CO remain confined near the surface, where they rapidly form a metallic Ni layer that inhibits further reduction. These results reveal distinct atomistic pathways for CO and H2 and provide insights that may guide metallurgical processes and catalyst design. 

Operandocharacterization reveals the structural dynamics of PtSn/SiO₂catalysts, hinting at a Pt-rich surface configuration for optimal propane dehydrogenation performance.