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<jats:sec> <jats:title>BACKGROUND</jats:title> <jats:p> As the world continues to transition toward carbon emissions–free energy technologies, there remains a need to also reduce the carbon emissions of the chemical production industry. Today many of the world’s chemicals are produced from fossil fuel–derived feedstocks. Electrochemical conversion of carbon dioxide (CO <jats:sub>2</jats:sub> ) into chemical feedstocks offers a way to turn waste emissions into valuable products, closing the carbon loop. When coupled to renewable sources of electricity, these products can be made with a net negative carbon emissions footprint, helping to sequester CO <jats:sub>2</jats:sub> into usable goods. Research and development into electrocatalytic materials for CO <jats:sub>2</jats:sub> reduction has intensified in recent years, with advances in selectivity, efficiency, and reaction rate progressing toward practical implementation. A variety of chemical products can be made from CO <jats:sub>2</jats:sub> , such as alcohols, oxygenates, synthesis gas (syngas), and olefins—staples in the global chemical industry. Because these products are produced at substantial scale, a switch to renewably powered production could result in a substantial carbon emissions reduction impact. The advancement of electrochemical technology to convert electrons generated from renewable power into stable chemical form also represents one avenue to long-term (e.g., seasonal) storage of energy. </jats:p> </jats:sec> <jats:sec> <jats:title>ADVANCES</jats:title> <jats:p> The science of electrocatalytic CO <jats:sub>2</jats:sub> reduction continues to progress, with priority given to the need to pinpoint more accurately the targets for practical application, the economics of chemical products, and barriers to market entry. It will be important to scale CO <jats:sub>2</jats:sub> electrolyzers and increase the stability of these catalysts to thousands of hours of continuous operation. Product separation and efficient recycling of CO <jats:sub>2</jats:sub> and electrolyte also need to be managed. The petrochemical industry operates at a massive scale with a complicated global supply chain and heavy capital costs. Commodity chemical markets are difficult to penetrate and are priced on feedstock, which is currently inexpensive as a result of the shale gas boom. CO <jats:sub>2</jats:sub> capture costs from the flue or direct air and product separation from unreacted CO <jats:sub>2</jats:sub> are also important to consider. Assuming that the advancement of electrocatalytic technologies continues apace, what will it take to disrupt the chemical production sector, and what will society gain by doing so? </jats:p> <jats:p> This review presents a technoeconomic and carbon emissions assessment of CO <jats:sub>2</jats:sub> products such as ethylene, ethanol, and carbon monoxide, offering target figures of merit for practical application. The price of electricity is by far the largest cost driver. Electrochemical production costs begin to match those of traditional fossil fuel–derived processes when electricity prices fall below 4 cents per kWh and energy conversion efficiencies reach at least 60%. When powered by renewable electricity, these products can be made with a net negative carbon emissions footprint. A comparative analysis of electrocatalytic, biocatalytic, and fossil fuel–derived chemical production shows that electrocatalytic production has the potential to yield the greatest reduction in carbon emissions, provided that a steady supply of clean electricity is available. Additionally, opportunities exist to combine electrochemical conversion of CO <jats:sub>2</jats:sub> with a range of other thermo- and biocatalytic processes to slowly electrify the existing petrochemical supply chain and further upgrade CO <jats:sub>2</jats:sub> into more useful chemicals. Technical challenges such as operating lifetime, energy efficiency, and product separation are discussed. Supply chain management of products and entrenched industrial petrochemical competition are also considered. </jats:p> </jats:sec> <jats:sec> <jats:title>OUTLOOK</jats:title> <jats:p> There exists increasingly widespread recognition of the need to transition to carbon emissions–free means of chemical production. CO <jats:sub>2</jats:sub> pricing mechanisms are being developed and are seeing increased governmental support. The nascent carbon utilization economy is gaining traction, with startup companies, global prizes, and industrial research efforts all pursuing new carbon conversion technologies. Recent advances in electrochemical CO <jats:sub>2</jats:sub> reduction through the use of gas diffusion electrodes are pushing current densities and selectivities into a realm of industrial use. Despite this progress, there remain technical challenges that must be overcome for commercial application. Additionally, market barriers and cost economics will ultimately decide whether this technology experiences widespread implementation. </jats:p> <jats:fig fig-type="figure" orientation="portrait" position="float"> <jats:caption> <jats:title> Electrochemical CO <jats:sub>2</jats:sub> conversion. </jats:title> <jats:p> Reduction of CO <jats:sub>2</jats:sub> using renewably sourced electricity could transform waste CO <jats:sub>2</jats:sub> emissions into commodity chemical feedstocks or fuels. </jats:p> </jats:caption> <jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" orientation="portrait" position="float" xlink:href="364_aav3506_fa.jpeg" /> </jats:fig> </jats:sec>

<jats:title>Domination in the stem cell world</jats:title> <jats:p> A Nobel Prize–winning discovery showed that specialized cells can be genetically reprogrammed into stem cells, thus gaining the ability to become any cell type in the body. But what happens during reprogramming is not completely understood. Shakiba <jats:italic>et al.</jats:italic> used experimental and mathematical approaches to show that skin cells compete during reprogramming, eliminating one another as the population progresses toward the stem cell state (see the Perspective by Wolff and Purvis). The “winners” are a special class of skin cells originating from the neural crest. Cells of this type normally emerge during embryonic development and migrate into various tissues, including the skin, muscle, and nervous system. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.aan0925">eaan0925</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6438" page="330" related-article-type="in-this-issue" vol="364" xlink:href="10.1126/science.aax1681">330</jats:related-article> </jats:p>

<jats:p>Imagine a world where affordable, quality health care is available to every person, and where infectious disease and infant and maternal mortality are as rare in the poorest parts as they are in wealthier countries. The world has already come a long way toward meeting this goal. But to finish the job, we need to change our thinking.</jats:p>

<jats:p>A roundup of weekly science policy and related news.</jats:p>

<jats:p>MD Anderson's moves stoke fear of ethnic profiling among Asian American scientists.</jats:p>

<jats:p>Telescopes to study gamma rays, gravitational waves, stars, and the sun take shape on the roof of the world.</jats:p>

<jats:p>Organization picks several science projects and helps them raise tens of millions of dollars from a network of donors.</jats:p>

<jats:p>Designer proteins kill soybean rust, a major threat that requires heavy fungicide use.</jats:p>

<jats:p>Warming is finishing off a decline that began 3000 years ago.</jats:p>