Advances of non-precious-metal catalysts for alkaline water electrolysis are reviewed, highlighting operando techniques and theoretical calculations in their development.

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The rational design of highly active and durable electrocatalysts for overall water splitting is a formidable challenge. In this work, a double perovskite oxide, i.e., NdBaMn2O5.5, is proposed as a bifunctional electrode material for water electrolysis. Layered NdBaMn2O5.5 demonstrates significant improvement in catalyzing oxygen and hydrogen evolution reactions (OER and HER, respectively), in contrast to other related materials, including disordered Nd0.5Ba0.5MnO3−δ as well as NdBaMn2O5.5−δ and NdBaMn2O5.5+δ (δ < 0.5). Importantly, NdBaMn2O5.5 has an OER intrinsic activity (∼24 times) and a mass activity (∼2.5 times) much higher than those of the benchmark RuO2 at 1.7 V versus the reversible hydrogen electrode. In addition, NdBaMn2O5.5 achieves a better overall water splitting activity at large potentials (>1.75 V) and catalytic durability in comparison to those of Pt/C–RuO2, making it a promising candidate electrode material for water electrolyzers. The substantially enhanced performance is attributed to the approximately half-filled eg orbit occupancy, optimized O p-band center location, and distorted structure. Interestingly, for the investigated perovskite oxides, OER and HER activity seem to be correlated; i.e., the material achieving a higher OER activity is also more active in catalyzing HER.

The presence of active metal nanoparticles on the surface significantly increases the electrochemical performance of ABO perovskite oxide materials. While conventional deposition methods can improve the activity, in situ exsolution produces nanoparticles with far greater stability. The migration of transition metal atoms toward the surface is expected to affect the exsolution process. To study the energetics, we use ab initio computations combined with experiments in a SrTiO-based model system. Our calculations show that Ni preferentially segregates toward the (100)-oriented and SrTiO-terminated surfaces, note that this orientation is identical to one reported by the Irvine and Gorte groups. Vacancies in the Sr-site and O-site promote the segregation of Ni, while placing La on the Sr-site has an opposite effect. The corresponding experiments are in agreement with the computational predictions. Fast nanoparticle growth and activity enhancement are found in STO system with Sr vacancies and without La. The approach developed in this Letter could be used to study the mechanism of exsolution in other material systems, and possibly lead to the development of new compositions capable of nanoparticle exsolution with higher activity and stability.

Solid‐state electrolytes (SEs) with high anodic (oxidation) stability are essential for achieving all‐solid‐state Li‐ion batteries (ASSLIBs) operating at high voltages. Until now, halide‐based SEs have been one of the most promising candidates due to their compatibility with cathodes and high ionic conductivity. However, the developed chloride and bromide SEs still show limited electrochemical stability that is inadequate for ultrahigh voltage operations. Herein, this challenge is addressed by designing a dual‐halogen Li‐ion conductor: Li3InCl4.8F1.2. F is demonstrated to selectively occupy a specific lattice site in a solid superionic conductor (Li3InCl6) to form a new dual‐halogen solid electrolyte (DHSE). With the incorporation of F, the Li3InCl4.8F1.2 DHSE becomes dense and maintains a room‐temperature ionic conductivity over 10−4 S cm−1. Moreover, the Li3InCl4.8F1.2 DHSE exhibits a practical anodic limit over 6 V (vs Li/Li+), which can enable high‐voltage ASSLIBs with decent cycling. Spectroscopic, computational, and electrochemical characterizations are combined to identify a rich F‐containing passivating cathode‐electrolyte interface (CEI) generated in situ, thus expanding the electrochemical window of Li3InCl4.8F1.2 DHSE and preventing the detrimental interfacial reactions at the cathode. This work provides a new design strategy for the fast Li‐ion conductors with high oxidation stability and shows great potential to high‐voltage ASSLIBs.

Calcium‐ion batteries (CIBs) are considered to be promising next‐generation energy storage systems because of the natural abundance of calcium and the multivalent calcium ions with low redox potential close to that of lithium. However, the practical realization of high‐energy and high‐power CIBs is elusive owing to the lack of suitable electrodes and the sluggish diffusion of calcium ions in most intercalation hosts. Herein, it is demonstrated that calcium‐ion intercalation can be remarkably fast and reversible in natural graphite, constituting the first step toward the realization of high‐power calcium electrodes. It is shown that a graphite electrode exhibits an exceptionally high rate capability up to 2 A g−1, delivering ≈75% of the specific capacity at 50 mA g−1 with full calcium intercalation in graphite corresponding to ≈97 mAh g−1. Moreover, the capacity stably maintains over 200 cycles without notable cycle degradation. It is found that the calcium ions are intercalated into graphite galleries with a staging process. The intercalation mechanisms of the “calciated” graphite are elucidated using a suite of techniques including synchrotron in situ X‐ray diffraction, nuclear magnetic resonance, and first‐principles calculations. The versatile intercalation chemistry of graphite observed here is expected to spur the development of high‐power CIBs.

A perovskite material with in situ exsolved Pt3Ni nanoparticles is applied for oxygen reduction reaction catalysis with dramatically improved activity.