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1. Recent advances of nonprecious and bifunctional electrocatalysts for overall water splitting

   https://doi.org/10.1039/D0SE00466A  

   Shang, Xiao; Tang, Jian-Hong; Dong, Bin; Sun, Yujie (June 2020, Sustainable Energy & Fuels)

   null (Ed.)

   Electrocatalytic water splitting to produce clean hydrogen is a promising technique for renewable energy conversion and storage in the future energy portfolio. Aiming at industrial hydrogen production, cost-effective electrocatalysts are expected to be competent in both hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs) to accomplish the overall water splitting. Limited by the low tolerance and/or poor activity of most 1st-row transition metal-based electrocatalysts in strongly acidic media, bifunctional electrocatalysts are currently advocated to work at high pH values. Herein, this review summarizes the recent progress of nonprecious bifunctional electrocatalysts for overall water splitting in alkaline media, including transition metal-based phosphides, chalcogenides, oxides, nitrides, carbides, borides, alloys, and metal-free materials. Besides, some prevalent modification strategies to optimize the activities of catalysts are briefly listed. Finally, the perspective on current challenges and future prospects for overall water splitting driven by advanced nonprecious electrocatalysts are briefly discussed. 

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2. A polymeric hydrogel electrocatalyst for direct water oxidation

   https://doi.org/10.1038/s41467-023-36532-x  

   Pei, Zengxia; Tan, Hao; Gu, Jinxing; Lu, Linguo; Zeng, Xin; Zhang, Tianqi; Wang, Cheng; Ding, Luyao; Cullen, Patrick J.; Chen, Zhongfang; et al (December 2023, Nature Communications)

   Abstract Metal-free electrocatalysts represent a main branch of active materials for oxygen evolution reaction (OER), but they excessively rely on functionalized conjugated carbon materials, which substantially restricts the screening of potential efficient carbonaceous electrocatalysts. Herein, we demonstrate that a mesostructured polyacrylate hydrogel can afford an unexpected and exceptional OER activity – on par with that of benchmark IrO 2 catalyst in alkaline electrolyte, together with a high durability and good adaptability in various pH environments. Combined theoretical and electrokinetic studies reveal that the positively charged carbon atoms within the carboxylate units are intrinsically active toward OER, and spectroscopic operando characterizations also identify the fingerprint superoxide intermediate generated on the polymeric hydrogel backbone. This work expands the scope of metal-free materials for OER by providing a new class of polymeric hydrogel electrocatalysts with huge extension potentials. 

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3. Metal-Nitrogen-Carbon Cluster Decorated Titanium Carbide is a Durable and Inexpensive Oxygen Reduction Reaction Electrocatalyst

   https://doi.org/doi:10.1002/cssc.202101341  

   Cho, S. B. (January 2021, ChemSusChem)

   null (Ed.)

   Clusters of nitrogen- and carbon-coordinated transition metals dispersed in a carbon matrix (e. g., Fe−N−C) have emerged as an inexpensive class of electrocatalysts for the oxygen reduction reaction (ORR). Here, it was shown that optimizing the interaction between the nitrogen-coordinated transition metal clusters embedded in a more stable and corrosion-resistant carbide matrix yielded an ORR electrocatalyst with enhanced activity and stability compared to Fe−N−C catalysts. Utilizing first-principles calculations, an electrostatics-based descriptor of catalytic activity was identified, and nitrogen-coordinated iron (FeN4) clusters embedded in a TiC matrix were predicted to be an efficient platinum-group metal (PGM)-free ORR electrocatalyst. Guided by theory, selected catalyst formulations were synthesized, and it was demonstrated that the experimentally observed trends in activity fell exactly in line with the descriptor-derived theoretical predictions. The Fe−N−TiC catalyst exhibited enhanced activity (20 %) and durability (3.5-fold improvement) compared to a traditional Fe−N−C catalyst. It was posited that the electrostatics-based descriptor provides a powerful platform for the design of active and stable PGM-free electrocatalysts and heterogenous single-atom catalysts for other electrochemical reactions. 

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4. Revised Nitrogen Reduction Scaling Relations from Potential-Dependent Modeling of Chemical and Electrochemical Steps

   https://doi.org/10.1021/acscatal.3c01978  

   Tezak, Cooper R.; Singstock, Nicholas R.; Alherz, Abdulaziz W.; Vigil-Fowler, Derek; Sutton, Christopher A.; Sundararaman, Ravishankar; Musgrave, Charles B. (October 2023, ACS Catalysis)

   The electrochemical nitrogen reduction reaction (NRR) is a promising route to enable carbon-free ammonia production. However, this reaction is limited by the poor activity and selectivity of current catalysts. The rational design of superior NRR electrocatalysts requires a detailed mechanistic understanding of current material limitations to inform how these might be overcome. The current understanding of how scaling limits NRR on metal catalysts is predicated on a simplified reaction pathway that considers only proton-coupled electron transfer (PCET) steps. Here, we apply grand-canonical density functional theory to investigate a more comprehensive NRR mechanism that includes both electrochemical and chemical steps on 30 metal surfaces in solvent under an applied potential. We applied Φmax, a grandcanonical adaptation of the Gmax thermodynamic descriptor, to evaluate trends in catalyst activity. This approach produces a Φmax “volcano” diagram for NRR activity scaling on metals that qualitatively differs from the scaling relations identified when only PCET steps are considered. NH3* desorption was found to limit the NRR activity for materials at the top of the volcano and truncate the volcano’s peak at increasingly reducing potentials. These revised scaling relations may inform the rational design of superior NRR electrocatalysts. This approach is transferable to study other materials and reaction chemistries where both electrochemical and chemical steps are modeled under an applied potential. 

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5. New monoclinic ruthenium dioxide with highly selective hydrogenation activity

   https://doi.org/10.1039/d2cy00815g  

   Yang, Hee Jung; Redington, Morgan; Miller, Daniel P.; Zurek, Eva; Kim, Minseob; Yoo, Choong-Shik; Lim, Soo Yeon; Cheong, Hyeonsik; Chae, Seen-Ae; Ahn, Docheon; et al (October 2022, Catalysis Science & Technology)

   Catalytic hydrogenation of aromatic compounds is an important industrial process, particularly for the production of many petrochemical and pharmaceutical derivatives. This reaction is mainly catalyzed by noble metals, but rarely by metal oxides. Here, we report the development of monoclinic hydrogen-bearing ruthenium dioxide with a nominal composition of H x RuO 2 that can serve as a standalone catalyst for various hydrogenation reactions. The hydrogen-bearing oxide was synthesized through the water gas shift reaction of CO and H 2 O in the presence of rutile RuO 2 . The structure of H x RuO 2 was determined by synchrotron X-ray diffraction and density functional theory (DFT) studies. Solid-state 1 H NMR and Raman studies suggest that this compound possesses two types of isolated interstitial protons. H x RuO 2 is very active in hydrogenation of various arenes, including liquid organic hydrogen carriers, which are completely converted to the corresponding fully hydrogenated products under relatively mild conditions. In addition, high selectivities (>99%) were observed for the catalytic hydrogenation of functionalized nitroarenes to corresponding anilines. DFT simulations yield a small barrier for concerted proton transfer. The facile proton dynamics may be key in enabling selective hydrogenation reactions at relatively low temperature. Our findings inspire the search for hydrogen-containing metal oxides that could be employed as high-performance materials for catalysts, electrocatalysts, and fuel cells. 

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