人工光合作用,誘人的清潔能源技術

Nature boasts some nifty technology. A leaf is one such miraculous machine, able to turn one form of energy into another: it takes in carbon dioxide, plus water, and uses sunlight to convert it all into carbohydrates.

大自然擁有一些奇妙的科技。葉子就是能將一種形式的能量轉化爲另一種的神奇機器：葉子吸收二氧化碳和水分，並利用陽光將其轉化爲碳水化合物。

For years, scientists have tried to emulate the process of photosynthesis. Finally, those efforts are blooming. The magazine Scientific American, together with experts from the World Economic Forum, has named the artificial leaf one of the breakthrough technologies of 2017.

多年來，科學家們一直試圖模仿光合作用。這些努力終於有了成果。《科學美國人》(Scientific American)雜誌與世界經濟論壇(WEF)的專家們將人工葉子評爲2017年的突破性技術之一。

Laboratory-based efforts are attempting to go one better on nature by generating not plant food but fuels that can be stored for later use. Such projects offer the promise of making new forms of energy while mopping up carbon dioxide, an unwanted greenhouse gas, from the atmosphere. That makes artificial photosynthesis one of the potentially cleanest technologies on the energy horizon.

實驗室研究人員正試圖比自然更勝一籌：不是生成植物養分，而是產生能夠儲存起來供以後使用的燃料。這類項目帶來了一種前景：在生產新型能源的同時，從大氣層吸走二氧化碳這種不受歡迎的溫室氣體。這使人工光合作用有望成爲能源領域最清潔的技術之一。

Daniel Nocera and Pamela Silver, from Harvard University, have taken early steps along this road. Their system — the “leaf” is actually a container — uses a catalyst, activated by sunlight, to split water molecules into hydrogen and oxygen molecules. The container is home to hydrogen-eating bacteria, which feast on the newly liberated molecules plus carbon dioxide to churn out liquid fuel.

哈佛大學(Harvard University)的丹尼爾?諾切拉(Daniel Nocera)和帕梅拉?西爾弗(Pamela Silver)是這條道路上的先行者。他們的系統，或者說“葉子”，實際上是一個容器，該系統利用一種由陽光激活的催化劑，把水分子分解成氫分子和氧分子。這個容器中有以氫爲食的細菌，這些細菌吞噬新釋放出的氫分子，再加上二氧化碳，來產出液體燃料。

While even the fastest-growing plants manage to convert about 1 per cent of sunlight into food, the Harvard scientists managed an efficiency of 10 per cent when using pure carbon dioxide. The efficiency drops to about 4 per cent when pulling carbon dioxide from the air.

即使是生長最快的植物，也只能將大約1%的陽光轉化爲養分，而哈佛大學的這兩位科學家研發的系統在利用純二氧化碳時，達到了10%的能量轉化效率。不過，如果從空氣中抽取二氧化碳，效率就會下降至約4%。

The sun is shining for solar fuels more widely. The US Department of Energy runs a specialist hub, the Joint Center for Artificial Photosynthesis, that brings together a host of academic institutions such as Caltech and the Lawrence Berkeley National Laboratory.

還有其他一些人在進行利用陽光製造太陽能燃料的研究。美國能源部(US Department of Energy)旗下有一個專門進行這方面研究的中心——人工光合作用聯合中心(Joint Center for Artificial Photosynthesis)，彙集了加利福尼亞理工學院(Caltech)和勞倫斯伯克利國家實驗室(Lawrence Berkeley National Laboratory)等一批學術機構。

Its mission is to develop a scalable technology that converts carbon dioxide, water and sunlight into renewable transportation fuels (even in a green future, trucks, planes and ships can’t be plugged into the grid while on the go). There are also a number of start-ups dedicated to transforming light energy into a storable, chemical alter ego; MIT Technology Review lists Opus12, Liquid Light, Joule Unlimited and LanzaTech. One challenge, among many, is to find cheap and plentiful catalysts; some techniques use platinum.

該中心的任務是開發一項可以大規模應用的技術，將二氧化碳、水和陽光轉化爲可再生的運輸用燃料（即使在一個綠色未來，卡車、飛機和船舶也不可能插着電線運行）。還有多家初創公司致力於將光能轉化爲可儲存的化學能；《麻省理工科技評論》(MIT Technology Review)列舉了Opus12、Liquid Light、Joule Unlimited和LanzaTech。其中一個挑戰是，找到廉價和取之不盡的催化劑；目前一些技術使用鉑作爲催化劑。

The excitement over artificial photosynthesis stems from its potential to create “dispatchable” renewable fuels, which can be stored and used when needed. In contrast, wind turbines and solar panels generate energy intermittently. That hurdle has hampered the bid to put renewables more firmly into the energy mix: one estimate, from the Cambridge University Science and Policy Exchange, contends that replacing the power supply of one coal-fired power station requires solar or wind substitutes to produce four times the output.

人工光合作用之所以令人振奮，是因爲它有可能製造出能夠儲存並在需要時使用的“可調遣的”可再生能源。與此形成反差的是，風力發電機和太陽能電池板只能斷斷續續地產生能量。這個問題阻礙了使可再生能源成爲能源結構中更可靠組成部分的努力：劍橋大學科學和政策交流中心(Cambridge University Science and Policy Exchange)進行的估測認爲，如果要用太陽能或風力發電來代替一座燃煤電廠的電力供應，前者的裝機容量要達到後者的4倍。

There is another bonus to solar fuels: they need no infrastructure. They can be whisked to even the remotest rural locations, with obvious implications for the developing world. Those advocating more public support of the technology point out it can be deployed quickly in places such as refugee camps and isolated villages undergoing disease outbreaks. For those reasons, Bill Gates declared himself an aficionado of the concept earlier this year. In March, he blogged: “I’ve written before about the need for an energy miracle to halt climate change and provide access to electricity to millions of the poorest families who live without it. Making solar fuel would be one of those miracles.” Mr Gates, among others, founded breakthrough energy ventures to invest $1bn in clean energy.

太陽能燃料還有一個好處：不需要基礎設施。它們可以被迅速送往最偏遠的農村地區，這對發展中國家來說顯然意義重大。呼籲公衆加大支持這種技術的人士指出，這種技術可以快速部署在難民營、疫情爆發的孤村等地方。出於這些理由，比爾?蓋茨(Bill Gates)在今年早些時候宣稱，他本人對這個概念心向神往。他在3月發佈博文稱：“我之前曾撰文說過，我們需要一個能源奇蹟來遏止氣候變化，同時讓數以百萬計目前尚未通電的最貧困家庭用上電。生產太陽能燃料將是這樣的奇蹟之一。”蓋茨和其他人創立了突破性能源風投基金，對清潔能源投資10億美元。

Artificial photosynthesis will also appeal to another class of consumer: those living off-grid. By 2035, Accenture estimates, 12 per cent of people in North America and 11 per cent in Europe will be energy self-sufficient and potentially living off-grid.

人工光合作用還將吸引另一個消費者羣體：過着“脫網”生活的人。埃森哲(Accenture)估計，到2035年，北美12%的人和歐洲11%的人將實現能源自足，可能會脫離電網。

Tesla has already anticipated the trend: the company’s Powerwall battery is designed to store solar power generated during the day so that it can be used at night, and is targeted at the same market. Indeed, a whole movement has sprung up around eco-living, with multiple books and websites offering blueprints for off-grid utopias, often powered by wood-chopping.

特斯拉(Tesla)已經預測到了這種趨勢：該公司的Powerwall電池能夠在白天儲存太陽能電力，以便在夜間使用，該產品瞄準同一個市場。實際上，圍繞着生態生活掀起了一陣浪潮，許多書籍和網站描繪了脫網生活的烏托邦藍圖，方法往往是砍柴。

This has inspired talk of a “death spiral” in the utilities industry: as renewables become cheaper, and with a huge infrastructure being serviced by a decreasing pool of customers, more will go off-grid. Enthusiasm for artificial photosynthesis, as with other renewables, is fuelled by green concerns too — and how fabulously post-modern that the cleanest way of going back to nature might be to fake it.

這引發了有關公用事業“死亡螺旋”的討論：隨着可再生能源變得更廉價，隨着越來越小的客戶羣要支撐起龐大的基礎設施，更多人將選擇“脫網”。對人工光合作用乃至其他可再生能源的熱情，還受到人們對環境憂慮的推波助瀾——要回歸自然，最清潔的方式可能是模仿自然，這是多麼詩意的後現代啊。