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1. Computational Analysis of Structure–Activity Relationships in Highly Active Homogeneous Ruthenium−Based Water Oxidation Catalysts

   https://doi.org/10.3390/catal12080863  

   Bury, Gabriel; Pushkar, Yulia (August 2022, Catalysts)

   Linear free−energy scaling relationships (LFESRs) and regression analysis may predict the catalytic performance of heterogeneous and recently, homogenous water oxidation catalysts (WOCs). This study analyses thirteen homogeneous Ru−based catalysts—some, the most active catalysts studied: the Ru(tpy−R)(QC) and Ru(tpy−R)(4−pic)2 complexes, where tpy is 2,2’;6’,2”terpyridine, QC is 8−quinolinecarboxylate and 4−pic is 4−picoline. Typical relationships studied among heterogenous catalysts cannot be applied to homogeneous catalysts. The selected group of structurally similar catalysts with impressive catalytic activity deserves closer computational and statistical analysis of multiple reaction step energetics correlating with measured catalytic activity. We report general methods of LFESR analysis yield insufficiently robust relationships between descriptor variables. However, volcano−plot−based analysis grounded in Sabatier’s principle reveals ideal relative energies of the RuIV = O and RuIV−OH intermediates and optimal changes in free energies of water nucleophilic attack on RuV = O. A narrow range of RuIV−OH to RuV = O redox potentials corresponding with the highest catalytic activities suggests facile access to the catalytically competent high−valent RuV = O state, often inaccessible from RuIV = O. Our work incorporates experimental oxygen evolution rates into approaches of LFESR and Sabatier−principle−based analysis, identifying a narrow yet fertile energetic landscape to bountiful oxygen evolution activity, leading to future rational design. 

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2. Degradation Mechanism of Calcium Iridium Oxide for Oxygen Evolution Reaction in Acid

   https://doi.org/10.1021/acs.energyfuels.3c01743  

   Li, Ruihan; Edgington, Jane; Seitz, Linsey C (September 2023, Energy & Fuels)

   The development of active and acid-stable iridium-based catalysts is crucial to meet the requirements of proton exchange membrane technologies for the sustainable production of hydrogen via water electrolysis. However, long-term stability remains a critical challenge. In this work, we focus on a Ca2IrO4 catalyst to develop a holistic picture of catalyst electronic and geometric structure evolution under various applied potentials by probing electrochemically active surface area, metal dissolution, Ir valence, and surface morphology. We observe an initial activity increase in parallel with increasing capacitance and minor iridium dissolution. Extensive chronoamperometry tests at oxidizing potentials lead to significant activity loss that occurs simultaneously with a dramatic drop in capacitance and a change in impedance. Using a combination of electrochemical and spectroscopic tools, we provide fundamental insights to these material degradation processes to enable future catalyst design with balanced activity and long-term stability. 

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3. Hydrogen peroxide synthesis on porous graphitic carbon nitride using water as a hydrogen source

   https://doi.org/10.1039/C9TA08103H  

   Cao, Yongyong; Zhou, Guobing; Chen, Xianlang; Qiao, Qi; Zhao, Chenxia; Sun, Xiang; Zhong, Xing; Zhuang, Guilin; Deng, Shengwei; Wei, Zhongzhe; et al (January 2020, Journal of Materials Chemistry A)

   null (Ed.)

   Using water as a hydrogen source is a promising strategy for alternative hydrogen peroxide (H 2 O 2 ) synthesis. By a series of ab initio molecular dynamics (AIMD) simulations and reactive molecular dynamics (RxMD) calculations, fundamental details have been revealed regarding how liquid water interacts with oxygen on a metal-free carbon nitride catalyst, and the two-step reaction mechanism of H 2 O 2 synthesis. Metal-free porous graphitic carbon nitride (g-C 5 N 2 ) catalysts are also systematically screened by using a thermodynamics approach through the ab initio density functional theory (DFT) method. Key results include: (a) pristine g-C 5 N 2 is most active to catalyze the H 2 O/O 2 reaction and produce H 2 O 2 ; (b) the adsorption and activation of water at unsaturated carbon sites of g-C 5 N 2 are critical to initiate the H 2 O/O 2 reaction, producing HOO* intermediates; (c) interfacial free water and adsorbed water at g-C 5 N 2 form a synergetic proton transfer cluster to promote HOO* intermediates to form H 2 O 2 . To the best of our knowledge, this work presents long-needed theoretical details of direct H 2 O 2 synthesis via the water/oxygen system, which can guide further optimization of carbon-based catalysts for oxygen reduction reactions. 

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4. Doping-modulated strain control of bifunctional electrocatalysis for rechargeable zinc–air batteries

   https://doi.org/10.1039/D1EE01271A  

   Li, Zhao; Wang, Qi; Bai, Xiaowan; Wang, Maoyu; Yang, Zhenzhong; Du, Yingge; Sterbinsky, George E.; Wu, Duojie; Yang, Zhenzhen; Tian, Huajun; et al (January 2021, Energy & Environmental Science)

   null (Ed.)

   Changes in the local atomic arrangement in a crystal caused by lattice-mismatch-induced strain can efficiently regulate the performance of electrocatalysts for zinc–air batteries (ZABs) in many manners, mainly due to modulated electronic structure configurations that affect the adsorption energies for oxygen-intermediates formed during oxygen reduction and evolution reactions (ORR and OER). However, the application of strain engineering in electrocatalysis has been limited by the strain relaxation caused by structural instability such as dissolution and destruction, leading to insufficient durability towards the ORR/OER. Herein, we propose a doping strategy to modulate the phase transition and formation of self-supported cobalt fluoride–sulfide (CoFS) nanoporous films using a low amount of copper (Cu) as a dopant. This well-defined Cu–CoFS heterostructure overcomes the obstacle of structural instability. Our study of the proposed Cu–CoFS also helps establish the structure–property relationship of strained electrocatalysts by unraveling the role of local strain in regulating the electronic structure of the catalyst. As a proof-of-concept, the Cu–CoFS electrocatalyst with doping-modulated strain exhibited superior onset potentials of 0.91 V and 1.49 V for the ORR and OER, respectively, surpassing commercial Pt/C@RuO 2 and benchmarking non-platinum group metal (non-PGM) catalysts. ZABs with the Cu–CoFS catalyst delivered excellent charge/discharge cycling performance with an extremely low voltage gap of 0.5 V at a current density of 10 mA cm −2 and successively 0.93 V at a high current density of 100 mA cm −2 and afforded an outstanding peak power density of 255 mW cm −2 . 

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5. Tunable Catalytic Performance of Palladium Nanoparticles for H2O2 Direct Synthesis via Surface-Bound Ligands

   https://doi.org/doi.org/10.1021/acscatal.0c01517  

   Lucas F. de L. e Freitas, Begoña Puértolas (April 2020, ACS catalysis)

   There is a critical need for sustainable routes to produce hydrogen peroxide, H2O2. A promising approach involves direct synthesis from molecular hydrogen and oxygen at (sub)ambient temperatures using unmodified supported Pd catalysts, which are limited by low selectivities. Controlling the environment of Pd active sites via surface ligands is shown to enhance selectivity. Trends among a myriad of surface ligands (i.e., phosphines, thiols, weakly bound molecules) suggest that those containing H-bonding groups lead to the highest H2O2 production, potentially by affecting reaction energetics via H-bonding with key intermediates. These insights lay the groundwork for ligand design to achieve the optimal catalyst performance for H2O2 synthesis. 

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