哈佛大学能源系教授丹尼尔·诺塞拉发明了一种能够模仿光合作用的人造叶子。然而，他不只是复制了大自然 – 而是超越了它。即使最高效的植物也只能把接触到的阳光的1%转变成能量，而这个人造版本是它的10倍。不过，它还处于早期研究阶段。要想利用这种方式产生经济效益，科学家们还要进行许多工作。

传统的硅基光伏电池利用光电效应（吸收光释放电子）来产生电流。诺塞拉的方法涉及到利用催化剂来加快化学反应。他说：“植物把氢与二氧化碳结合起来，形成糖分燃料。我们发现，可以从叶片中提取氢，然后利用合成生物学的方法，通过细菌将二氧化碳和氢转变为液态烃燃料和塑料化学前体。”

不幸的是，电池含有的镍合金会损害细菌的DNA。2017年，诺塞拉又发明了一个替代品，即钴催化剂。意外的是，这个新的催化剂不产生碳氢燃料，而是把太阳能源转变成生物质，效率为柳枝稷的10倍。进一步处理可以产生生物醇，碳氢燃料等。

不过，这项技术应用到市场上还需要几年甚至更久的研发。科学家们需要先克服一些问题。现在利用人造叶造氢的成本是利用化石燃料的10倍左右。为了缩小价格差距，技术研发员需要简化系统的制造及安装过程。与此同时，还需要确认这些系统的寿命和其他太阳能系统相近，即20年左右。这做起来可并不容易。

一些常见的问题有，从水中产生的氧气使液体酸化，导致电极和催化剂被损害。对低pH忍耐能力比较强的物质成本要更高。诺塞拉的解决方案是，让催化剂拥有自我修复的能力。另一种可能的解决方案是涂上一层导电氧化薄膜（也是防晒霜的主要成分）来保护电极和催化剂。此外其他方面依然有很多地方需要改良。

在缺乏传统能源设施的地方，利用人造叶制造氢和燃料，从成本上看可能没有太大的问题。在这些地方无论采取什么方式燃料都是昂贵的。国家可以把原本花在烧煤发电场等产生大量污染的地方的钱投资于由人造光合作用供电的分散式系统。也许，人造叶将会成为绿色能源的新潮流。

翻译：凯瑟琳·奥尔森（Katherine Olson）

来源：Mega 2018年7月28日刊

Besting Nature

Harvard University Professor of Energy Daniel Nocera has developed an artificial leaf chip to mimic photosynthesis. But more than just copying nature, Nocera’s technology outdoes it. While the most efficient plants can convert about 1 per cent of sunlight into energy, manmade versions could produce at least 10 times better results—though it’s early days yet. Considerable work remains to be done before the technology could produce power in a commercially useful way.

 Traditional silicon-based photovoltaic cells rely on the photoelectric effect—absorbed light triggering the release of electrons—to generate a current that can power something or charge a battery. Nocera’s method involves speeding up chemical reactions with a catalyst. “Plants take hydrogen in the dark and combine it with carbon dioxide to make fuel” in the form of sugars, he says. “We realised you can take the hydrogen from artificial leaves and then, using the tools of synthetic biology, engineer bacteria“ to convert the hydrogen and carbon dioxide to liquid hydrocarbon fuels as well as plastic chemical precursors.

Unfortunately, the nickel alloy in his cell in effect poisoned the bacteria by damaging its DNA. But 2017, Nocera, came up with a replacement, a new cobalt-based catalyst. Except now, rather than generating hydrocarbons, the solar cell converted solar energy into biomass—at a 10-fold greater efficiency than fast-growing crops like switch grass—that could then be converted into fuels like bioalcohols and hydrocarbon fuels with a further stage.

This technology’s commercial applications are, however, probably years away, if not more. There are several hurdles that must be overcome first. Today’s methods for making hydrogen from an artificial leaf are likely to cost 10 times more than just making it from fossil fuels. To reduce the cost gap, the technology’s developers need to simplify making and installing their systems and to ensure they can last as long as other solar options, which is about 20 years—not always an easy feat.

For instance, producing oxygen from water, makes the solution acidic, which can damage the electrodes and catalysts. Materials that can survive the acidity tend to be expensive. Nocera’s solution was to make his catalysts self-healing. Another possible solution is a thin coating of conducting oxide films—the active ingredient in sunscreen—can protect the electrodes and catalysts, but there’s plenty of work still to be done on other aspects.

The price of making hydrogen from an artificial leaf and fuels from the bionic leaf might not matter as much in places that lack conventional energy infrastructure. In these sorts of places, no matter what approach is taken, fuel will be expensive. Rather than spend on a polluting source of power, like a coal plant, a country could invest in distributed systems powered by artificial photosynthesis. Eventually, artificial leaves could be the new wave of green energy.