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1. Direct Evidence of Local pH Change and the Role of Alkali Cation during CO 2 Electroreduction in Aqueous Media

   https://doi.org/10.1002/anie.201912637  

   Zhang, Fen ; Co, Anne C. ( December 2019 , Angewandte Chemie International Edition)

   We report, for the first time, utilizing a rotating ring‐disc electrode (RRDE) assembly for detecting changes in the local pH during aqueous CO₂reduction reaction (CO₂RR). Using Au as a model catalyst where CO is the only product, we show that the CO oxidation peak shifts by −86±2 mV/pH during CO₂RR, which can be used to directly quantify the change in the local pH near the catalyst surface during electrolysis. We then applied this methodology to investigate the role of cations in affecting the local pH during CO₂RR and find that during CO₂RR to CO on Au in an MHCO₃buffer (where M is an alkali metal), the experimentally measured local basicity decreased in the order Li⁺> Na⁺> K⁺> Cs⁺, which agreed with an earlier theoretical prediction by Singh et al. Our results also reveal that the formation of CO is independent of the cation. In summary, RRDE is a versatile tool for detecting local pH change over a diverse range of CO₂RR catalysts. Additionally, using the product itself (i.e. CO) as the local pH probe allows us to investigate CO₂RR without the interference of additional probe molecules introduced to the system. Most importantly, considering that most CO₂RR products have pH‐dependent oxidation, RRDE can be a powerful tool for determining the local pH and correlating the local pH to reaction selectivity.

    

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2. Direct Evidence of Local pH Change and the Role of Alkali Cation during CO 2 Electroreduction in Aqueous Media

   https://doi.org/10.1002/ange.201912637  

   Zhang, Fen ; Co, Anne C. ( December 2019 , Angewandte Chemie)

   We report, for the first time, utilizing a rotating ring‐disc electrode (RRDE) assembly for detecting changes in the local pH during aqueous CO₂reduction reaction (CO₂RR). Using Au as a model catalyst where CO is the only product, we show that the CO oxidation peak shifts by −86±2 mV/pH during CO₂RR, which can be used to directly quantify the change in the local pH near the catalyst surface during electrolysis. We then applied this methodology to investigate the role of cations in affecting the local pH during CO₂RR and find that during CO₂RR to CO on Au in an MHCO₃buffer (where M is an alkali metal), the experimentally measured local basicity decreased in the order Li⁺> Na⁺> K⁺> Cs⁺, which agreed with an earlier theoretical prediction by Singh et al. Our results also reveal that the formation of CO is independent of the cation. In summary, RRDE is a versatile tool for detecting local pH change over a diverse range of CO₂RR catalysts. Additionally, using the product itself (i.e. CO) as the local pH probe allows us to investigate CO₂RR without the interference of additional probe molecules introduced to the system. Most importantly, considering that most CO₂RR products have pH‐dependent oxidation, RRDE can be a powerful tool for determining the local pH and correlating the local pH to reaction selectivity.

    

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3. Designing CO 2 reduction electrode materials by morphology and interface engineering

   https://doi.org/10.1039/d0ee00900h  

   Pan, Fuping ; Yang, Yang ( August 2020 , Energy & Environmental Science)

   null (Ed.)

   Electrochemical reduction of CO 2 into value-added fuels and chemicals driven by renewable energy presents a potentially sustainable route to mitigate CO 2 emissions and alleviate the dependence on fossil fuels. While tailoring the electronic structure of active components to modulate their intrinsic reactivity could tune the CO 2 reduction reaction (CO 2 RR), their use is limited by the linear scaling relation of intermediates. Due to the high susceptibility of the CO 2 RR to the local CO 2 concentration/pH and mass transportation of CO 2 /intermediates/products near the gas–solid–liquid three-phase interface, engineering catalysts’ morphological and interfacial properties holds great promise to regulate the CO 2 RR, which are irrelevant with linear scaling relation and possess high resistance to harsh reaction conditions. Herein, we provide a comprehensive overview of recent advances in tuning CO 2 reduction electrocatalysis via morphology and interface engineering. The fundamentals of the CO 2 RR and design principles for electrode materials are presented firstly. Then, approaches to build an efficient three-phase interface, tune the surface wettability, and design a favorable morphology are summarized; the relationship between the properties of engineered catalysts and their CO 2 RR performance is highlighted to reveal the activity-determining parameters and underlying catalytic mechanisms. Finally, challenges and opportunities are proposed to suggest the future design of advanced CO 2 RR electrode materials. 

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4. A High-Pressure System for Studying Oxygen Reduction During Pt Nanoparticle Collisions

   https://doi.org/10.1149/1945-7111/abcde2  

   Zhang, Yulun ; Robinson, Donald A. ; McKelvey, Kim ; Ren, Hang ; White, Henry S. ; Edwards, Martin A. ( December 2020 , Journal of The Electrochemical Society)

   Here we report measurements of the oxygen reduction reaction (ORR) at single Pt nanoparticles (NPs) through their collision with a Au microdisk electrode of lower electrocatalytic activity. Performing measurements at an elevated pressure (10-atm, pure O₂) raises the O₂concentration ∼50-fold over air-saturated measurements, allowing the ORR activity of smaller Pt NPs to be resolved and quantified, compared to measurements taken at atmospheric pressure. Single-NP ORR current vs potential measurements for 2.6, 16, and 24 nm radius citrate-capped Pt NPs, show the catalytic activity of the smallest Pt NPs to be roughly one order of magnitude greater than the activity of the larger NPs. The particle-by-particle nature of our measurement quantifies the distribution of electrocatalytic activities of individual particles, which we determine to be larger than can be explained by the distribution of particle sizes. Additionally, we report that some of the observed ORR current transients contain multiple sharp peaks per single-NP measurement, indicating multiple collisions of a single Pt NP at the electrode surface.

    

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5. Sub‐6 nm Fully Ordered L 1 0 ‐Pt–Ni–Co Nanoparticles Enhance Oxygen Reduction via Co Doping Induced Ferromagnetism Enhancement and Optimized Surface Strain

   https://doi.org/10.1002/aenm.201803771  

   Wang, Tanyuan ; Liang, Jiashun ; Zhao, Zhonglong ; Li, Shenzhou ; Lu, Gang ; Xia, Zhengcai ; Wang, Chao ; Luo, Jiahuan ; Han, Jiantao ; Ma, Cheng ; et al ( March 2019 , Advanced Energy Materials)

   Engineering the crystal structure of Pt–M (M = transition metal) nanoalloys to chemically ordered ones has drawn increasing attention in oxygen reduction reaction (ORR) electrocatalysis due to their high resistance against M etching in acid. Although Pt–Ni alloy nanoparticles (NPs) have demonstrated respectable initial ORR activity in acid, their stability remains a big challenge due to the fast etching of Ni. In this work, sub‐6 nm monodisperse chemically orderedL1₀‐Pt–Ni–Co NPs are synthesized for the first time by employing a bifunctional core/shell Pt/NiCoO_xprecursor, which could provide abundant O‐vacancies for facilitated Pt/Ni/Co atom diffusion and prevent NP sintering during thermal annealing. Further, Co doping is found to remarkably enhance the ferromagnetism (room temperature coercivity reaching 2.1 kOe) and the consequent chemical ordering ofL1₀‐Pt–Ni NPs. As a result, the best‐performing carbon supportedL1₀‐PtNi_0.8Co_0.2catalyst reveals a half‐wave potential (E_1/2) of 0.951 V versus reversible hydrogen electrode in 0.1mHClO₄with 23‐times enhancement in mass activity over the commercial Pt/C catalyst along with much improved stability. Density functional theory (DFT) calculations suggest that theL1₀‐PtNi_0.8Co_0.2core could tune the surface strain of the Pt shell toward optimized Pt–O binding energy and facilitated reaction rate, thereby improving the ORR electrocatalysis.

    

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