Three-dimensional open nano-netcage electrocatalysts for efficient pH-universal overall water splitting

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...

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Section: Porous Iridium-based Electrocatalysts For Acidic Oermentioning

confidence: 99%

Active Site Engineering in Porous Electrocatalysts

et al. 2020

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“…To date, various catalysts including Ir‐based, [ 8 ] Ru‐based, [ 9 ] Co‐based, [ 10 ] Ni‐based, [ 11 ] and Mn‐based [ 12 ] oxides have been developed for the OER in neutral electrolytes, and Ru–Ir oxide was reported to possess the highest intrinsic activity among them. [ 9 ] However, even with the use of such Ru–Ir oxide catalysts, as reported so far, the OER overpotentials in neutral electrolyte are much higher than that in acidic or alkaline electrolyte, limiting the overall energy efficiencies of these applications. [ 13 ]…”

Section: Figurementioning

confidence: 99%

Boosting Neutral Water Oxidation through Surface Oxygen Modulation

et al. 2020

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Developing efficient electrocatalysts for oxygen evolution reaction (OER) in pH‐neutral electrolyte is crucial for microbial electrolysis cells and electrochemical CO2 reduction. Unfortunately, the OER kinetics in neutral electrolyte is sluggish due to the low concentration of adsorbed reactants, with overpotentials of neutral OER at present much higher than that in acidic or alkaline electrolyte. Here, hydrated metal cations (Ca2+) are sought to be incorporated into the state‐of‐the‐art Ru–Ir binary oxide to tailor the surface oxygen environments (lattice‐oxygen and adsorbed oxygen species) for efficient neutral OER. Using a sol–gel method, ternary Ru–Ir–Ca oxides are synthesized in atomically homogenous manner, and the obtained catalyst on glassy carbon electrode achieves 10 mA cm−2 at a low overpotential of 250 mV, with no degradation for 200 h of operation. In situ X‐ray absorption spectroscopy, in situ 18O isotope‐labeling differential electrochemical mass spectrometry, and 18O isotope‐labeling secondary ion mass spectroscopy studies are carried out. The results reveal that incorporation of Ca2+ can enhance the covalency of metal–oxygen bonds and the electrophilic nature of surface metal‐bonded oxygen sites; and simultaneously facilitate the adsorption of water molecules on catalyst surface, which accelerates the lattice‐oxygen‐involved reaction, thus improving the overall OER performance of RuIrCaOx catalyst.

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“…The results of underpotentially deposited hydrogen (H upd ) and methanol oxidation experiments unravel that the high intrinsic catalytic activities originate from the optimized hydrogen and oxygen intermediates binding energies, which can accelerate both kinetics of HER and OER. At the atomic level, density functional theory (DFT) and operando X-ray absorption fine structure (XAFS) spectroscopy investigations validate that such optimum binding energies are induced by the unique electronic state and coordination environment of Ir sites bonded with both N and S. Interestingly, the Ir-NSG catalyst displays superb performance when integrated directly as both the anode and cathode electrodes in a water electrolysis cell at all pH values, reaching a geometric current density of 10 mA cm −2 with as low as 300, 190, and 220 mV overpotential for overall water splitting in neutral, acidic, and alkaline electrolyte, respectively, serving as a promising candidate for next-generation water-splitting technologies 21 .…”

Section: Introductionmentioning

confidence: 99%

Coordination engineering of iridium nanocluster bifunctional electrocatalyst for highly efficient and pH-universal overall water splitting

et al. 2020

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Water electrolysis offers a promising energy conversion and storage technology for mitigating the global energy and environmental crisis, but there still lack highly efficient and pHuniversal electrocatalysts to boost the sluggish kinetics for both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Herein, we report uniformly dispersed iridium nanoclusters embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for both HER and OER at all pH conditions, reaching a current density of 10 mA cm −2 with only 300, 190 and 220 mV overpotential for overall water splitting in neutral, acidic and alkaline electrolyte, respectively. Based on probing experiments, operando X-ray absorption spectroscopy and theoretical calculations, we attribute the high catalytic activities to the optimum bindings to hydrogen (for HER) and oxygenated intermediate species (for OER) derived from the tunable and favorable electronic state of the iridium sites coordinated with both nitrogen and sulfur.

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Three-dimensional open nano-netcage electrocatalysts for efficient pH-universal overall water splitting

Cited by 305 publications

References 58 publications

Active Site Engineering in Porous Electrocatalysts

Active Site Engineering in Porous Electrocatalysts

Boosting Neutral Water Oxidation through Surface Oxygen Modulation

Coordination engineering of iridium nanocluster bifunctional electrocatalyst for highly efficient and pH-universal overall water splitting

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