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1. Effect of Carbon Doping on CO ₂ ‐Reduction Activity of Single Cobalt Sites in Graphitic Carbon Nitride

   https://doi.org/10.1002/cnma.202100164  

   Huang, Peipei; Huang, Jiahao; Li, Junying; Zhang, Lei; He, Jie; Caputo, Christine_A; Frenkel, Anatoly_I; Li, Gonghu (June 2021, ChemNanoMat)

   Abstract Single‐atom catalysts have demonstrated interesting activity in a variety of applications. In this study, we prepared single Co²⁺sites on graphitic carbon nitride (C₃N₄), which was doped with carbon for enhanced activity in visible‐light CO₂reduction. The synthesized materials were characterized with a variety of techniques, including microscopy, X‐ray powder diffraction, UV‐vis spectroscopy, infrared spectroscopy, photoluminescence spectroscopy, and X‐ray absorption spectroscopy. Doping C₃N₄with carbon was found to have profound effect on the photocatalytic activity of the single Co²⁺sites. At relatively low levels, carbon doping enhanced the photoresponse of C₃N₄in the visible region and improved charge separation upon photoactivation, thereby enhancing the photocatalytic activity. High levels of carbon doping were found to be detrimental to the photocatalytic activity of the single Co²⁺sites by altering the structure of C₃N₄and generating defect sites responsible for charge recombination. 

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2. Resolving the Carbon‐Climate Feedback Potential of Wetland CO ₂ and CH ₄ Fluxes in Alaska

   https://doi.org/10.1029/2022GB007524  

   Ma, Shuang; Bloom, A. Anthony; Watts, Jennifer D.; Quetin, Gregory R.; Donatella, Zona; Euskirchen, Eugénie S.; Norton, Alexander J.; Yin, Yi; Levine, Paul A.; Braghiere, Renato K.; et al (September 2023, Global Biogeochemical Cycles)

   Abstract Boreal‐Arctic regions are key stores of organic carbon (C) and play a major role in the greenhouse gas balance of high‐latitude ecosystems. The carbon‐climate (C‐climate) feedback potential of northern high‐latitude ecosystems remains poorly understood due to uncertainty in temperature and precipitation controls on carbon dioxide (CO₂) uptake and the decomposition of soil C into CO₂and methane (CH₄) fluxes. While CH₄fluxes account for a smaller component of the C balance, the climatic impact of CH₄outweighs CO₂(28–34 times larger global warming potential on a 100‐year scale), highlighting the need to jointly resolve the climatic sensitivities of both CO₂and CH₄. Here, we jointly constrain a terrestrial biosphere model with in situ CO₂and CH₄flux observations at seven eddy covariance sites using a data‐model integration approach to resolve the integrated environmental controls on land‐atmosphere CO₂and CH₄exchanges in Alaska. Based on the combined CO₂and CH₄flux responses to climate variables, we find that 1970‐present climate trends will induce positive C‐climate feedback at all tundra sites, and negative C‐climate feedback at the boreal and shrub fen sites. The positive C‐climate feedback at the tundra sites is predominantly driven by increased CH₄emissions while the negative C‐climate feedback at the boreal site is predominantly driven by increased CO₂uptake (80% from decreased heterotrophic respiration, and 20% from increased photosynthesis). Our study demonstrates the need for joint observational constraints on CO₂and CH₄biogeochemical processes—and their associated climatic sensitivities—for resolving the sign and magnitude of high‐latitude ecosystem C‐climate feedback in the coming decades. 

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3. Hybrid Organic‐Inorganic Heterogeneous Interfaces for Electrocatalysis: A Theoretical Study of CO ₂ Reduction to C ₂

   https://doi.org/10.1002/cctc.202101224  

   Wan, Mingyu; Gu, Zhiyong; Che, Fanglin (December 2021, ChemCatChem)

   Abstract Hybrid organic‐inorganic heterogeneous catalytic interfaces, where traditional catalytic materials are modified with self‐assembled monolayers (SAMs), create promising features to control a wide range of catalytic processes through the design of dual organic‐inorganic active sites and the induced confinement effect. To provide a fundamental insight, we investigated CO₂electroreduction into valuable C₂chemicals (CO₂RR‐to‐C₂) over SAM‐modulated Cu. Our theoretical results show that 1/4 monolayer aminothiolates improve the stability, activity and selectivity of CO₂RR‐to‐C₂by: (1) decreasing surface energy to suppress surface reconstruction; (2) facilitating CO₂activation and C−C coupling through dual organic‐inorganic (i. e., −NH, Cu) active sites; (3) promoting C−C coupling via confinement effects that enlarge the adsorption energy difference between CO^*and COH^*; (4) inducing local electric fields to Cu surface and changing its dipole moment and polarizability to be in favor of C−C coupling under electrode/electrolyte interfacial electric field. 

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4. ¹ H‐decoupling and Isotopic Labeling for the Measurement of the Longitudinal Relaxation Time of Hyperpolarized ¹³ C‐Methylenes in Choline Analogs

   https://doi.org/10.1002/ijch.201900016  

   Uppala, Sivaranjan; Gamliel, Ayelet; Harris, Talia; Sosna, Jacob; Gomori, J. Moshe; Jerschow, Alexej; Katz‐Brull, Rachel (April 2019, Israel Journal of Chemistry)

   Abstract The T₁of a hyperpolarized site in solution is a key parameter that determines the time‐window in which its NMR signals are observable. For¹³C sites adjacent to protons,¹H‐decoupling has been shown to increase the hyperpolarized signal resolution and SNR. Additionally, polarization transfer to protons has shown utility in increasing the sensitivity of detection. However,¹H‐decoupling could lead to a change in the decay rate of a hyperpolarized¹³C site. Here we tested this possible effect in a case where the protons are directly bound to an sp³hyperpolarized¹³C site (using [1,2‐¹³C₂]choline) and¹H‐decoupling was applied continuously throughout the hyperpolarized decay measurement. We found that¹H‐decoupling did not lead to any significant changes in the¹³C polarization decay time but did result in the expected collapse of J‐coupling and produced sharper signals. This result suggested that¹H‐decoupling did not affect the decay rate of hyperpolarized sp^{3 13}C sites. The deuterium‐substitution approach (using [1,1,2,2‐D₄,1‐¹³C]choline) showed a dramatic prolongation of T₁. Upper bounds on the T₁of all investigated sites were calculated. 

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5. Nonlinear Growth and Physiological Responses of White Spruce at North American Arctic Treeline

   https://doi.org/10.1029/2022JG007096  

   Lévesque, Mathieu; Andreu‐Hayles, Laia; D’Arrigo, Rosanne; Oelkers, Rose; Buckley, Brendan M. (April 2023, Journal of Geophysical Research: Biogeosciences)

   Abstract Much is still unknown about the growth and physiological responses of trees to global change at the northern treeline. We combined tree‐ring width data with century‐long stable carbon and oxygen isotope records to investigate growth and physiological responses of white spruce at two treeline sites in the Canadian Arctic to concurrent increases in temperature, atmospheric CO₂concentration (c_a), and decline in sea ice extent over the past century. The tree‐ring records were assessed during three periods with contrasting climatic conditions: (a) the early 20th century warming, (b) the 1940–1970 cooling period, and (c) the anthropogenic late 20th century warming period. We found opposing growth trends between the two sites, but similar carbon isotope discrimination (Δ¹³C) and intrinsic water‐use efficiency (_iWUE) trajectories. While tree growth (defined as basal area increment) increased at the site nearer to the Arctic Ocean during the 20th century following the rise in temperature and sea ice loss, growth declined after 1950 at the more interior site. At both sites, Δ¹³C slightly increased over these periods. However, trees showed a nonlinear response to increasedc_a, shifting after 1970 from a passive stomatal response (i.e., no changes in_iWUE) to an active response (i.e., a moderate ∼12% increase in_iWUE). Further, our isotope‐based findings do not support the idea that temperature‐induced drought stress caused the divergent growth trends at our treeline sites. This study thus highlights nonlinear and complex physiological and growth adjustments to concomitant changes in temperature, sea ice extent, andc_aover the last century at the northern treeline. 

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