A major challenge in the field of water electrolysis is the scarcity of oxygen-evolving catalysts that are inexpensive, highly corrosion-resistant, suitable for large-scale applications and able to oxidize water at high current densities and low overpotentials. Most unsupported, non-precious metals oxygen-evolution catalysts require at least ~350 mV overpotential to oxidize water with a current density of 10 mA/cm2 in 1 M alkaline solution. Here we report on a robust nanostructured porous NiFe-based oxygen evolution catalyst made by selective alloy corrosion. In 1 M KOH, our material exhibits a catalytic activity towards water oxidation of 500 mA/cm2 at 360 mV overpotential and is stable for over eleven days. This exceptional performance is attributed to three factors. First, the small size of the ligaments and pores in our mesoporous catalyst (~10 nm) results in a high BET surface area (43 m2/g) and therefore a high density of oxygen-evolution catalytic sites per unit mass. Second, the open porosity facilitates effective mass transfer at the catalyst/electrolyte interface. Third and finally, the high bulk electrical conductivity of the mesoporous catalyst allows for effective current flow through the electrocatalyst, making it possible to use thick films with a high density of active sites and ~3×104 cm2 of catalytic area per cm2 of electrode area. Our mesoporous catalyst is thus attractive for alkaline electrolyzers where water-based solutions are decomposed into hydrogen and oxygen as the only products, driven either conventionally or by photovoltaics.

We have synthesized nanoporous Au with a dual microscopic length scale by exploiting the crystal structure of the alloy precursor. The synthesized mesoscopic material is characterized by stacked Au layers of submicrometer thickness. In addition, each layer displays nanoporosity through the entire bulk. It is shown that the thickness of these layers can be tailored via the grain size of the alloy precursor. The two-length-scale structure enhances the functional properties of nanoporous gold, leading to charge-induced strains of amplitude up to 6%, which are roughly 2 orders of magnitude larger than in nanoporous Au with the standard one-length-scale porous morphology. A model is presented to describe these phenomena.

Prolonged decomposition of electrolytes forming a thick and unstable solid-electrolyte interphase (SEI) continues to be a major bottleneck in designing sodium-ion batteries (SIBs). We have carried out quantum chemistry simulations to investigate the fundamental mechanisms of reduction-induced decomposition of electrolyte solvents in the vicinity of a sodium ion. Kinetics and thermodynamics of several reaction pathways for one-and two-electron reduction of ethylene carbonate (EC) have been examined. Our calculations indicate that the high reduction potential and low barrier for the ring opening of EC is the main cause for the continuous growth of SEI observed in SIBs. The impact of two well-known electrolyte additives, vinyl carbonate (VC) and fluoroethylene carbonate (FEC), on SEI composition was evaluated by studying decomposition pathways of (1) VC and FEC molecules in the bulk EC solvent and (2) an EC molecule in a supermolecular cluster comprising an EC and the additive molecule. The additive molecules have significantly low barriers for decomposition and therefore decompose first. Additionally, the presence of an additive molecule was also shown to increase the barrier for decomposition of EC. Another observation suggests that the preferred reduction state of an EC molecule changes when it forms a dimer with additive molecules, and these reduction states have different decomposition pathways which leads to formation of different SEI compounds. On the basis of these observations, we predict that not only do the additive molecules protect solvent molecules from reductive decomposition but also they can promote alternate pathways for the decomposition, leading to qualitatively different and potentially stable SEI products.

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There are still many scientific and engineering challenges that need to be addressed before a true sustainable hydrogen economy can be realized. Three of these challenges include sustainable hydrogen generation without CO2 emissions, effective storage of this hydrogen for specific applications, and expanding the limited existing hydrogen infrastructure. Here we demonstrate (i) the fabrication of hierarchical bulk nanoporous aluminum with the coexistence of macroscopic and mesoscopic ligament/pore structures, with the mesoscopic ligaments in the range of 10–20 nm; (ii) the use of this aluminum to produce hydrogen on-site with a yield of ∼52–90% by hydrolysis with “pure” water, without incorporation of any catalyst or reaction promoter in the aluminum-water system; and (iii) the combustion of this aluminum in air under ambient conditions, which implies that this material could be attractive as a combustion fuel catalyst, e.g., to enhance the ignition and combustion of solid propellants. The inclusion of secondary aluminum or carbon-free primary aluminum in our process will make it possible to produce hydrogen with reduced carbon footprint for on-site and on-board applications using only nanoporous aluminum and water.