Although a number of nonprecious materials can exhibit catalytic activity approaching (sometimes even outperforming) that of iridium oxide catalysts for the oxygen evolution reaction, their catalytic lifetimes rarely exceed more than several hundred hours under operating conditions. Here we develop an energy-efficient, cost-effective, scaled-up corrosion engineering method for transforming inexpensive iron substrates (e.g., iron plate and iron foam) into highly active and ultrastable electrodes for oxygen evolution reaction. This synthetic method is achieved via a desired corrosion reaction of iron substrates with oxygen in aqueous solutions containing divalent cations (e.g., nickel) at ambient temperature. This process results in the growth on iron substrates of thin film nanosheet arrays that consist of iron-containing layered double hydroxides, instead of rust. This inexpensive and simple manufacturing technique affords iron-substrate-derived electrodes possessing excellent catalytic activities and activity retention for over 6000 hours at 1000 mA cm-2 current densities.

Developing nonprecious hydrogen evolution electrocatalysts that can work well at large current densities (e.g., at 1000 mA/cm: a value that is relevant for practical, large-scale applications) is of great importance for realizing a viable water-splitting technology. Herein we present a combined theoretical and experimental study that leads to the identification of α-phase molybdenum diboride (α-MoB) comprising borophene subunits as a noble metal-free, superefficient electrocatalyst for the hydrogen evolution reaction (HER). Our theoretical finding indicates, unlike the surfaces of Pt- and MoS-based catalysts, those of α-MoB can maintain high catalytic activity for HER even at very high hydrogen coverage and attain a high density of efficient catalytic active sites. Experiments confirm α-MoB can deliver large current densities in the order of 1000 mA/cm, and also has excellent catalytic stability during HER. The theoretical and experimental results show α-MoB's catalytic activity, especially at large current densities, is due to its high conductivity, large density of efficient catalytic active sites and good mass transport property.

Making highly efficient catalysts for an overall ​water splitting reaction is vitally important to bring solar/electrical‐to‐hydrogen energy conversion processes into reality. Herein, the synthesis of ultrathin nanosheet‐based, hollow MoOx/Ni3S2 composite microsphere catalysts on nickel foam, using ammonium molybdate as a precursor and the triblock copolymer pluronic P123 as a structure‐directing agent is reported. It is also shown that the resulting materials can serve as bifunctional, non‐noble metal electrocatalysts with high activity and stability for the hydrogen evolution reaction (HER) as well as the oxygen evolution reaction (OER). Thanks to their unique structural features, the materials give an impressive water‐splitting current density of 10 mA cm−2 at ≈1.45 V with remarkable durability for >100 h when used as catalysts both at the cathode and the anode sides of an alkaline electrolyzer. This performance for an overall water splitting reaction is better than even those obtained with an electrolyzer consisting of noble metal‐based Pt/C and IrOx/C catalytic couple—the benchmark catalysts for HER and OER, respectively.

Developing nonprecious oxygen evolution electrocatalysts that can work well at large current densities is of primary importance in a viable water-splitting technology. Herein, a facile ultrafast (5 s) synthetic approach is reported that produces a novel, efficient, non-noble metal oxygen-evolution nano-electrocatalyst that is composed of amorphous Ni-Fe bimetallic hydroxide film-coated, nickel foam (NF)-supported, Ni S nanosheet arrays. The composite nanomaterial (denoted as Ni-Fe-OH@Ni S /NF) shows highly efficient electrocatalytic activity toward oxygen evolution reaction (OER) at large current densities, even in the order of 1000 mA cm . Ni-Fe-OH@Ni S /NF also gives an excellent catalytic stability toward OER both in 1 m KOH solution and in 30 wt% KOH solution. Further experimental results indicate that the effective integration of high catalytic reactivity, high structural stability, and high electronic conductivity into a single material system makes Ni-Fe-OH@Ni S /NF a remarkable catalytic ability for OER at large current densities.

Splitting water to produce hydrogen requires the development of non-noble-metal catalysts that are able to make this reaction feasible and energy efficient. Herein, we show that cobalt pentlandite (Co9S8) nanoparticles can serve as an electrochemically active, noble-metal-free material toward hydrogen evolution reaction, and they work stably in neutral solution (pH 7) but not in acidic (pH 0) and basic (pH 14) media. We, therefore, further present a carbon-armoring strategy to increase the durability and activity of Co9S8 over a wider pH range. In particular, carbon-armored Co9S8 nanoparticles (Co9S8@C) are prepared by direct thermal treatment of a mixture of cobalt nitrate and trithiocyanuric acid at 700 °C in N2 atmosphere. Trithiocyanuric acid functions as both sulfur and carbon sources in the reaction system. The resulting Co9S8@C material operates well with high activity over a broad pH range, from pH 0 to 14, and gives nearly 100% Faradaic yield during hydrogen evolution reaction under acidic (pH 0), neutral (pH 7), and basic (pH 14) media. To the best of our knowledge, this is the first time that a transition-metal chalcogenide material is shown to have all-pH efficient and durable electrocatalytic activity. Identifying Co9S8 as the catalytically active phase and developing carbon-armoring as the improvement strategy are anticipated to give a fresh impetus to rational design of high-performance noble-metal-free water splitting catalysts.

between electrical and chemical energy to store off-peak electricity produced from these resources. The opportunities relate to the fact that electrocatalytic reactions can be employed to convert these excess and off-peak electricity into chemical bonds in molecules. A fascinating prospect is the utilization of renewable electricity for the conversion of abundant resources such as H 2 O, N 2 , and CO 2 into synthetic fuels such as hydrogen, ammonia, hydrocarbons, and alcohols under ambient conditions (Figure 1). Through the reverse processes, clean electricity can be generated from the products, for example, via hydrogen-, ammonia-, or alcohol-powered fuel cells, ultimately resulting in a closed water cycle, nitrogen cycle, or carbon cycle. Hydrogen production via electrocatalytic water splitting, which may enable the hydrogen economy, is a notable example to these. [2] At present, the annual hydrogen production worldwide exceeds more than 65 million tons, mainly for industrial uses such as petroleum refining and ammonia synthesis. Unfortunately, most of the hydrogen is produced from fossil fuels through steam methane reforming and coal gasification and is accompanied by large emission of the greenhouse gas CO 2. Producing hydrogen from water using renewable electricity provides a green and sustainable pathway for future hydrogen energy cycle. In a similar vein, renewable energy-powered electrocatalysis of CO 2 and N 2 reduction produces high-value fuels or fine chemicals such as formic acid (HCOOH), carbon monoxide (CO), methanol (CH 3 OH), and ammonia (NH 3) under ambient conditions. [3] The use of these renewable fuels (e.g., hydrogen and alcohols), instead of petroleum-based fuels, for transportation applications is receiving unprecedented attention because the former are more environmentally friendly and sustainable. Fuel cell technologies based on these fuels can reliably supply electrical energy and are, thus, highly desired for running emerging electric vehicles. [4] To realize the water cycle, carbon cycle, and nitrogen cycle described above, the central reactions are the hydrogen evolution reaction (HER), the CO 2 reduction reaction (CO 2 RR), and the nitrogen reduction reaction (NRR), as well as the oxygenrelated reactions, including the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), which are important half reactions in electrolyzers and fuel cells, respectively. In these energy conversion processes, electrocatalysts are indispensable. The desired electrocatalysts should both Electrocatalysis is at the center of many sustainable energy conversion technologies that are being developed to reduce the dependence on fossil fuels. The past decade has witnessed significant progresses in the exploitation of advanced electrocatalysts for diverse electrochemical reactions involved in electrolyzers and fuel cells, such as the hydrogen evolution reaction (HER), the oxygen reduction reaction (ORR), the CO 2 reduction reaction (CO 2 RR), the nitrogen reduction reaction (NRR), and the oxyge...

Water splitting requires nonprecious materials that can catalyze efficiently both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Here, we report the synthesis of mackinawite FeS nanosheets grown on iron foam, which can serve as an efficient pre-electrocatalyst for both HER and OER in alkaline media. During electrochemical HER testing, core@shell iron@iron oxysulfide nanoparticles as the catalytically active phase are generated in situ on FeS nanosheets. During electrochemical OER testing, FeS nanosheets totally transform into porous amorphous FeO x film that can mediate the OER efficiently. When assembled as the cathode and the anode in a single electrolyzer, the resulting Fe-based catalysts can give a good overall watersplitting output that outperforms the one obtained from a noble-metal-based Pt/C-IrO 2-coupled electrolyzer. These results provide new insights on the active sites of Fe-based catalysts as well as an impetus for further research on low-cost, iron-containing water-splitting electrocatalysts.

Superefficient water-splitting materials comprising sub-nanometric copper clusters and quasi-amorphous cobalt sulfide supported on copper foam are reported. While working together at both the anode and cathode sides of an alkaline electrolyzer, this material gives a catalytic output of overall water splitting comparable with the Pt/C-IrO -coupled electrolyzer.