Zapping elderly brains with electricity improves short-term memory — for almost an hour

Electric Buses reduce urban emissions and noise, but require charging infrastructure, grid upgrades, and depot redesigns; they offer lower operating costs and simpler maintenance, with range limits influencing routes, schedules, and on-route fast charging.

Key Points

Battery-electric buses cut emissions and noise while lowering operating and maintenance costs for transit agencies.

✅ Lower emissions, noise; improved rider experience

✅ Requires charging, grid upgrades, depot redesigns

✅ Range limits affect routes; on-route fast charging helps

In lots of ways, the electric bus feels like a technology whose time has come. Transportation is responsible for about a quarter of global emissions, and those emissions are growing faster than in any other sector. While buses are just a small slice of the worldwide vehicle fleet, they have an outsize effect on the environment. That’s partly because they’re so dirty—one Bogotá bus fleet made up just 5 percent of the city’s total vehicles, but a quarter of its CO2, 40 percent of nitrogen oxide, and more than half of all its particulate matter vehicle emissions. And because buses operate exactly where the people are concentrated, we feel the effects that much more acutely.

Enter the electric bus. Depending on the “cleanliness” of the electric grid into which they’re plugged, e-buses are much better for the environment. They’re also just straight up nicer to be around: less vibration, less noise, zero exhaust. Plus, in the long term, e-buses have lower operating costs, and related efforts like US school bus electrification are gathering pace too.

So it makes sense that global e-bus sales increased by 32 percent last year, according to a report from Bloomberg New Energy Finance, as the age of electric cars accelerates across markets worldwide. “You look across the electrification of cars, trucks—it’s buses that are leading this revolution,” says David Warren, the director of sustainable transportation at bus manufacturer New Flyer.

Today, about 17 percent of the world’s buses are electric—425,000 in total. But 99 percent of them are in China, where a national mandate promotes all sorts of electric vehicles. In North America, a few cities have bought a few electric buses, or at least run limited pilots, to test the concept out, and early deployments like Edmonton's first e-bus offer useful lessons as systems ramp up. California has even mandated that by 2029 all buses purchased by its mass transit agencies be zero-emission.

But given all the benefits of e-buses, why aren’t there more? And why aren’t they everywhere?

“We want to be responsive, we want to be innovative, we want to pilot new technologies and we’re committed to doing so as an agency,” says Becky Collins, the manager of corporate initiative at the Southeastern Pennsylvania Transportation Authority, which is currently on its second e-bus pilot program. “But if the diesel bus was a first-generation car phone, we’re verging on smartphone territory right now. It’s not as simple as just flipping a switch.”

One reason is trepidation about the actual electric vehicle. Some of the major bus manufacturers are still getting over their skis, production-wise. During early tests in places like Belo Horizonte, Brazil, e-buses had trouble getting over steep hills with full passenger loads. Albuquerque, New Mexico, canceled a 15-bus deal with the Chinese manufacturer BYD after finding equipment problems during testing. (The city also sued). Today’s buses get around 225 miles per charge, depending on topography and weather conditions, which means they have to re-up about once a day on a shorter route in a dense city. That’s an issue in a lot of places.

If you want to buy an electric bus, you need to buy into an entire electric bus system. The vehicle is just the start.

The number one thing people seem to forget about electric buses is that they need to get charged, and emerging projects such as a bus depot charging hub illustrate how infrastructure can scale. “We talk to many different organizations that get so fixated on the vehicles,” says Camron Gorguinpour, the global senior manager for the electric vehicles at the World Resources Institute, a research organization, which last month released twin reports on electric bus adoption. “The actual charging stations get lost in the mix.”

But charging stations are expensive—about $50,000 for your standard depot-based one. On-route charging stations, an appealing option for longer bus routes, can be two or three times that. And that’s not even counting construction costs. Or the cost of new land: In densely packed urban centers, movements inside bus depots can be tightly orchestrated to accommodate parking and fueling. New electric bus infrastructure means rethinking limited space, and operators can look to Toronto's TTC e-bus fleet for practical lessons on depot design. And it’s a particular pain when agencies are transitioning between diesel and electric buses. “The big issue is just maintaining two sets of fueling infrastructure,” says Hanjiro Ambrose, a doctoral student at UC Davis who studies transportation technology and policy.

“We talk to many different organizations that get so fixated on the vehicles. The actual charging stations get lost in the mix as the American EV boom gathers pace across sectors.”

Then agencies also have to get the actual electricity to their charging stations. This involves lengthy conversations with utilities about grid upgrades, rethinking how systems are wired, occasionally building new substations, and, sometimes, cutting deals on electric output, since electric truck fleets will also strain power systems in parallel. Because an entirely electrified bus fleet? It’s a lot to charge. Warren, the New Flyer executive, estimates it could take 150 megawatt-hours of electricity to keep a 300-bus depot charged up throughout the day. Your typical American household, by contrast, consumes 7 percent of that—per year. “That’s a lot of work by the utility company,” says Warren.

For cities outside of China—many of them still testing out electric buses and figuring out how they fit into their larger fleets—learning about what it takes to run one is part of the process. This, of course, takes money. It also takes time. Optimists say e-buses are more of a question of when than if. Bloomberg New Energy Finance projects that just under 60 percent of all fleet buses will be electric by 2040, compared to under 40 percent of commercial vans and 30 percent of passenger vehicles.

Which means, of course, that the work has just started. “With new technology, it always feels great when it shows up,” says Ambrose. “You really hope that first mile is beautiful, because the shine will come off. That’s always true.”

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Canada Net-Zero Grid Lessons highlight Europe's energy transition risks: Germany's power prices, wind and solar variability, nuclear phaseout, grid reliability, storage, market design, policy reforms, and distributed energy resources for resilient decarbonization.

Key Points

Lessons stress an all-of-the-above mix, robust market design, storage, and nuclear to ensure reliability, affordability.

✅ Diversify: nuclear, hydro, wind, solar, storage for reliability.

✅ Reform markets and grid planning for integration and flexibility.

✅ Build fast: streamline permitting, invest in transmission and DERs.

Europe is currently suffering the consequences of an uncoordinated rush to carbon-free electricity that experts warn could hit Canada as well unless urgent action is taken.

Power prices in Germany, for example, hit a record 91 euros ($135 CAD) per megawatt-hour earlier this month. That is more than triple what electricity costs in Ontario, where greening the grid could require massive investment, even during periods of peak demand.

Experts blame the price spikes in large part on a chaotic transition to a specific set of renewable electricity sources - wind and solar - at the expense of other carbon-free supplies such as nuclear power. Germany, Europe’s largest economy, plans to close its last remaining nuclear power plant next year despite warnings that renewables are not being added to the German grid quickly enough to replace that lost supply.

As Canada prepares to transition its own electricity grid to 100 per cent net-zero supplies by 2035, with provinces like Ontario planning new wind and solar procurement, experts say the European power crisis offers lessons this country must heed in order to avoid a similar fate.

'A CAUTIONARY TALE'
“Some countries have rushed their transition without thinking about what people need and when they need it,” said Chris Bentley, managing director of Ryerson University’s Legal Innovation Zone who also served as Ontario’s Minister of Energy from 2011 to 2013, in an interview. “Germany has experienced a little bit of this issue recently when the wind wasn’t blowing.”

Wind power usually provides between 20 and 30 per cent of Germany’s electricity needs, but the below-average breeze across much of continental Europe in recent months has pushed that figure down.

“There is a cautionary tale from the experience in Europe,” said Francis Bradley, chief executive officer of the Canadian Electricity Association, in an interview. “There was also a cautionary tale from what took place this past winter in Texas,” he added, referring to widespread power failures in Texas spawned by a lack of backup power supplies during an unusually cold winter that led to many deaths.

The first lesson Canada must learn from those cautionary tales, Bradley said, “is the need to pursue an all-of-the-above approach.”

“It is absolutely essential that every opportunity and every potential technology for low-carbon or no-carbon electricity needs to be pursued and needs to be pursued to the fullest,” he said.

The more important lesson for Canada, according to Binnu Jeyakumar, is about the need for a more holistic, nuanced approach to our own net-zero transition.

“It is very easy to have runaway narratives that just pinpoint the blame on one or two issues, but the lesson here isn’t really about the reliability of renewables as there are failures that occur across all sources of electricity supply,” said Jeyakumar, director of clean energy for the Pembina Institute, in an interview. 

“The takeaway for us is that we need to get better at learning how to integrate an increasingly diverse electricity grid,” she said. “It is not necessarily the technologies themselves, it is about how we do grid planning, how are our markets structured and are we adapting them to the trends that are evolving in the electricity and energy sectors.”
 

'ABSOLUTELY ENORMOUS' CHALLENGE IS 'ALMOST MIND-BENDING'
Canada already gets the vast majority of its electricity from emission-free sources. Hydro provides roughly 60 per cent of our power, nuclear contributes another 15 per cent and renewables such as wind and solar contribute roughly seven per cent more, according to federal government data.

Tempting as it might be to view the remaining 18 per cent of Canadian electricity that is supplied by oil, natural gas and coal as a small enough proportion that it should be relatively easy to replace, with some analyses warning that scrapping coal abruptly can be costly for consumers, the reality is much more difficult.

“It is the law of diminishing returns or the 80-20 rule where the first 80 per cent is easy but the last 20 per cent is hard,” Bradley explained. “We already have an electricity sector that is 80 per cent GHG-free, so getting rid of that last 20 per cent is the really difficult part because the low-hanging fruit has already been picked.”

Key to successfully decarbonizing Canada’s power grid will be the recognition that electricity demand is constantly growing, a point reinforced by a recent power challenges report that underscores the scale. That means Canada needs to build out enough emission-free power sources to replace existing fossil fuel-based supplies while also ensuring adequate supplies for future demand.

“It is one thing to say that by 2035 we are going to have a decarbonized electricity system, but the challenge really is the amount of additional electricity that we are going to need between now and 2035,” said John Gorman, chief executive officer of the Canadian Nuclear Association, which has argued that nuclear is key to climate goals in Canada, and former CEO of the Canadian Solar Industries Association, in an interview. “It is absolutely enormous, I mean, it is almost mind-bending.”

Canada will need to triple the amount of electricity produced nationwide by 2050, according to a report from SNC-Lavalin published earlier this year, and provinces such as Ontario face a shortfall over the next few years, Gorman said. Gorman said that will require adding between five and seven gigawatts of new installed capacity to Canada’s electricity grid every year from 2021 through 2050 or more than twice the amount of new power supply Canada brings online annually right now.

For perspective, consider Ontario’s Bruce Power nuclear facility. It took 27 years to bring that plant to its current 6.4 gigawatt (GW) capacity, but meeting Canada’s decarbonization goals will require adding roughly the equivalent capacity of Bruce Power every year for the next three decades.

“The task of creating enough electricity in the coming years is truly enormous and governments have not really wrapped their heads around that yet,” Gorman said. “For those of us in the energy sector, it is the type of thing that can keep you up at night.”

GOVERNMENT POLICY 'HELD HOSTAGE' BY 'DINOSAURS'
The Pembina Institute’s Jeyakumar agreed “the last mile is often the most difficult” and will require “a concerted effort both at the federal level and the provincial level.”

Governments will “need to be able to support innovation and solutions such as non-wires alternatives,” she said. “Instead of building a massive new transmission line or beefing up an old one, you could put a storage facility at the end of an existing line. Distributed energy resources provide those kinds of non-wires alternatives and they are already cost-effective and competitive with oil and gas.”

For Glen Murray, who served as Ontario’s minister of infrastructure and transportation from early 2013 to mid-2014 before assuming the environment and climate change portfolio until his resignation in mid-2017, that is a key lesson governments have yet to learn.

“We are moving away from a centralized distribution model to distributed systems where individual buildings and homes and communities will supply their own electricity needs,” said Murray, who currently works for an urban planning software company in Winnipeg, in an interview. “Yet both the federal and provincial governments are assuming that we are going to continue to have large, centralized generation of power, but that is simply not going to be the case.”

“Government policy is not focused on driving that because they are held hostage by their own hydro utilities and the big gas companies,” Murray said. “They are controlling the agenda even though they are the dinosaurs.”

Referencing the SNC-Lavalin report, Gorman noted as many as 45 small, modular nuclear reactors as well as 20 conventional nuclear power plants will be required in the coming decades, with jurisdictions like Ontario exploring new large-scale nuclear as part of that mix: “And that is in the context of also maximizing all the other emission-free electricity sources we have available as well from wind to solar to hydro and marine renewables,” Gorman said, echoing the “all-of-the-above” mindset of the Canadian Electricity Association.

There are, however, “fundamental rules of the market and the regulatory system that make it an uneven playing field for these new technologies to compete,” said Jeyakumar, agreeing with Murray’s concerns. “These are all solvable problems but we need to work on them now.”
 

'2035 IS TOMORROW'
According to Bentley, the former Ontario energy minister-turned academic, “the government's role is to match the aspiration with the means to achieve that aspiration.”

“We have spent far more time as governments talking about the goals and the high-level promises [of a net-zero electricity grid by 2035] without spending as much time as we need to in order to recognize what a massive transformation this will mean,” Bentley said. “It is easy to talk about the end-goal, but how do you get there?”

The Canadian Electricity Assocation’s Bradley agreed “there are still a lot of outstanding questions about how we are going to turn those aspirations into actual policies. The 2035 goal is going to be very difficult to achieve in the absence of seeing exactly what the policies are that are going to move us in that direction.”

“It can take a decade to go through the processes of consultations and planning and then building and getting online,” Bradley said. “Particularly when you’re talking about big electricity projects, 2035 is tomorrow.”

Jeyakumar said “we cannot afford to wait any longer” for policies to be put in place as the decisions governments make today “will then lock us in for the next 30 or 40 years into specific technologies.”

“We need to consider it like saving for retirement,” said Gorman of the Canadian Nuclear Association. “Every year that you don’t contribute to your retirement savings just pushes your retirement one more year into the future.”

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New York Utility Disconnection Ban protects residents during state emergencies, covering electric, gas, water, telecommunications, cable, and internet services, with penalties for noncompliance and options like deferred payment agreements and consumer protections.

Key Points

A proposed law barring shutoffs in state emergencies across electric, gas, water, telecom, cable, and internet.

✅ Applies during declared state and local emergencies statewide.

✅ Covers electric, gas, water, telecom, cable, and internet services.

✅ Noncompliance triggers penalties; payment plans required for arrears.

Governor Andrew M. Cuomo has announced a proposal to prohibit utility disconnections in regions that are under a state of emergency, addressing the energy insecurity many households face, as part of the 2021 State of the State. The Governor will propose legislation that will apply to electric, gas, water, telecommunications, cable and internet services. Utilities that fail to comply will be subject to penalties.

“In a year in which we dealt with an unprecedented pandemic, ferocious storms added insult to injury by knocking out power for hundreds of thousands of New Yorkers,” Governor Cuomo said. “Utility companies provide essential services, and we need to make sure they continue to provide them, rain or shine. That’s why we’re proposing legislation to make sure that New Yorkers, especially those living in regions under states of emergency, have access to these critical services to provide for themselves and their families.”

Governor Cuomo has taken a series of actions to protect New Yorkers’ access to utilities during the COVID-19 pandemic, including a suspension of shut-offs in New York and New Jersey, among other measures. Last year, the Governor signed legislation extending a moratorium that prevents utility companies from disconnecting utilities to residential households that are struggling with their bills due to the COVID-19 pandemic, a move mirrored by reconnection efforts in Ontario by Hydro One. Utility companies must instead offer these individuals a deferred payment agreement on any past-due balance. 

On November 19, Governor Cuomo announced that Con Edison now faces $25 million in penalties and possible license revocation from the New York State Public Service Commission, amid a broader review of retail energy markets by state regulators, following an investigation into the utility’s failed response during large-scale power outages in Manhattan and Brooklyn in July 2019. On November 2, Governor Cuomo announced that more than $328 million in home heating aid is now available, similar to Ontario bill support during the pandemic, for low- and middle-income New Yorkers who need assistance keeping their homes warm during the coming winter season.

The Governor has previously enacted some of the strongest and most progressive consumer protection and assistance programs in the country, including smart streetlights in Syracuse that reduce energy costs, and other initiatives. Governor Cuomo established New York’s energy affordability policy in 2016, as states pursue renewable energy ambitions that can affect rates, underscoring the need for affordability. The policy extended energy bill support to more than 152,000 additional New York families, ensuring that more than 920,000 New York families spend no more than 6 percent of their income on energy bills. Through this program, New York commits more than $238 million annually helping to keep the lights and heat on for our most vulnerable New Yorkers, while actively striving to expand coverage to additional families.

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US Control of Ukraine Nuclear Plants sparks debate over ZNPP, Zaporizhzhia, sovereignty, safety, ownership, and international cooperation, as Washington touts utility expertise, investment, and modernization to protect critical energy infrastructure amid conflict.

Key Points

US management proposal for Ukraine's nuclear assets, notably ZNPP, balancing sovereignty, safety, and investment.

✅ Ukraine retains ownership; any transfer requires parliament approval.

✅ ZNPP safety risks persist amid occupation near active conflict.

✅ International reactions split: sovereignty vs. cooperation and investment.

In a recent phone call with Ukrainian President Volodymyr Zelenskyy, U.S. President Donald Trump proposed that the United States take control of Ukraine's nuclear power plants, including the Zaporizhzhia Nuclear Power Plant (ZNPP), which has been under Russian occupation since early in the war and where Russia is reportedly building power lines to reactivate the plant amid ongoing tensions. Trump suggested that American ownership of these plants could be the best protection for their infrastructure, a proposal that has sparked controversy in policy circles, and that the U.S. could assist in running them with its electricity and utility expertise.

Ukrainian Response

President Zelenskyy promptly addressed Trump's proposal, stating that while the conversation focused on the ZNPP, the issue of ownership was not discussed. He emphasized that all of Ukraine's nuclear power plants belong to the Ukrainian people and that any transfer of ownership would require parliamentary approval . Zelenskyy clarified that while the U.S. could invest in and help modernize the ZNPP, ownership would remain with Ukraine.

Security Concerns

The ZNPP, Europe's largest nuclear facility, has been non-operational since its occupation by Russian forces in 2022. The plant's location near active conflict zones raises significant safety risks that the IAEA has warned of in connection with attacks on Ukraine's power grids, and its future remains uncertain. Ukrainian officials have expressed concerns about potential Russian provocations, such as explosions, especially after UN inspectors reported mines at the Zaporizhzhia plant near key facilities, if and when Ukraine attempts to regain control of the plant.

International Reactions

The proposal has elicited mixed reactions both within Ukraine and internationally. Some Ukrainian officials view it as an opportunistic move by the U.S. to gain control over critical infrastructure, while others see it as a potential avenue for modernization and investment, alongside expanding wind power that is harder to destroy in wartime. The international community remains divided on the issue, with some supporting Ukraine's sovereignty over its nuclear assets and others advocating for a possible agreement on power plant attacks to ensure the plant's safety and future operation.

President Trump's proposal to have the U.S. take control of Ukraine's nuclear power plants has sparked significant controversy. While the U.S. offers expertise and investment, Ukraine maintains that ownership of its nuclear assets is a matter of national sovereignty, even as it has resumed electricity exports to bolster its economy. The situation underscores the complex interplay between security, sovereignty, and international cooperation in conflict zones.

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Small Modular Reactors in Canada are advancing through provincial collaboration, offering nuclear energy, clean power and carbon reductions for grids, remote communities, and mines, with factory-built modules, regulatory roadmaps, and pre-licensing by the nuclear regulator.

Key Points

Compact, factory-built nuclear units for clean power, cutting carbon for grids, remote communities, and industry.

✅ Provinces: Ontario, Saskatchewan, New Brunswick collaborate

✅ Targets coal replacement, carbon cuts, clean baseload power

✅ Modular, factory-made units; 5-10 year deployment horizon

The premiers of Ontario, Saskatchewan and New Brunswick have committed to collaborate on developing nuclear reactor technology in Canada. 

Doug Ford, Scott Moe and Blaine Higgs made the announcement and signed a memorandum of understanding on Sunday in advance of a meeting of all the premiers. 

They will be working on the research, development and building of small modular reactors as a way to help their individual provinces reduce carbon emissions and move away from non-renewable energy sources like coal. 

Small modular reactors are easy to construct, are safer than large reactors and are regarded as cleaner energy than coal, the premiers say. They can be small enough to fit in a school gym. 

SMRs are actually not very close to entering operation in Canada, though Ontario broke ground on its first SMR at Darlington recently, signaling early progress. Natural Resources Canada released an "SMR roadmap" last year, with a series of recommendations about regulation readiness and waste management for SMRs.

In Canada, about a dozen companies are currently in pre-licensing with the Canadian Nuclear Safety Commission, which is reviewing their designs.

"Canadians working together, like we are here today, from coast to coast, can play an even larger role in addressing climate change in Canada and around the world," Moe said.  

Canada's Paris targets are to lower total emissions 30 per cent below 2005 levels by 2030, and nuclear's role in climate goals has been emphasized by the federal minister in recent remarks. Moe says the reactors would help Saskatchewan reach a 70 per cent reduction by that year.

The provinces' three energy ministries will meet in the new year to discuss how to move forward and by the fall a fully-fledged strategy for the reactors is expected to be ready.

However, don't expect to see them popping up in a nearby field anytime soon. It's estimated it will take five to 10 years before they're built. 

Ford lauds economic possibilities
The provincial leaders said it could be an opportunity for economic growth, estimating the Canadian market for this energy at $10 billion and the global market at $150 billion.

Ford called it an "opportunity for Canada to be a true leader." At a time when Ottawa and the provinces are at odds, Higgs said it's the perfect time to show unity. 

"It's showing how provinces come together on issues of the future." 

P.E.I. premier predicts unity at Toronto premiers' meeting
No other premiers have signed on to the deal at this point, but Ford said all are welcome and "the more, the merrier."

But developing new energy technologies is a daunting task. Higgs admitted the project will need national support of some kind, though he didn't specify what. The agreement signed by the premiers is also not binding. 

About 8.6 per cent of Canada's electricity comes from coal-fired generation. In New Brunswick that figure is much higher — 15.8 per cent — and New Brunswick's small-nuclear debate has intensified as New Brunswick Premier Blaine Higgs has said he worries about his province's energy producers being hit by the federal carbon tax.

Ontario has no coal-fired power plants, and OPG's SMR commitment aligns with its clean electricity strategy today. In Saskatchewan, burning coal generates 46.6 per cent of the province's electricity.

How would it work?
The federal government describes small modular reactors (SMRs) as the "next wave of innovation" in nuclear energy technology, and collaborations like the OPG and TVA partnership are advancing development efforts, and an "important technology opportunity for Canada."

Traditional nuclear reactors used in Canada typically generate about 800 megawatts of electricity, and Ontario is exploring new large-scale nuclear plants alongside SMRs, or enough to power about 600,000 homes at once (assuming that 1 megawatt can power about 750 homes).

The International Atomic Energy Agency (IAEA), the UN organization for nuclear co-operation, considers a nuclear reactor to be "small" if it generates under 300 megawatts.

Designs for small reactors ranging from just 3 megawatts to 300 megawatts have been submitted to Canada's nuclear regulator, the Canadian Nuclear Safety Commission, for review as part of a pre-licensing process, while plans for four SMRs at Darlington outline a potential build-out pathway that regulators will assess.

Ford rallying premiers to call for large increase in federal health transfers
Such reactors are considered "modular" because they're designed to work either independently or as modules in a bigger complex (as is already the case with traditional, larger reactors at most Canadian nuclear power plants). A power plant could be expanded incrementally by adding additional modules.

Modules are generally designed to be small enough to make in a factory and be transported easily — for example, via a standard shipping container.

In Canada, there are three main areas where SMRs could be used:

Traditional, on-grid power generation, especially in provinces looking for zero-emissions replacements for CO2-emitting coal plants.
Remote communities that currently rely on polluting diesel generation.
Resource extraction sites, such as mining and oil and gas.
 

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Polycrystalline Tin Selenide Thermoelectrics enable waste heat recovery with ZT 3.1, matching single crystals while cutting costs, powering greener car engines, industrial furnaces, and thermoelectric generators via p-type and emerging n-type designs.

Key Points

Low-cost tin selenide devices that turn waste heat into power, achieving ZT 3.1 and enabling p-type and n-type modules.

✅ Oxygen removal prevents heat-leaking tin oxide grain skins.

✅ Polycrystalline ingots match single-crystal ZT 3.1 at lower cost.

✅ N-type tin selenide in development to pair with p-type.

So-called thermoelectric generators turn waste heat into electricity without producing greenhouse gas emissions, providing what seems like a free lunch. But despite helping power the Mars rovers, the high cost of these devices has prevented their widespread use. Now, researchers have found a way to make cheap thermoelectrics that work just as well as the pricey kind. The work could pave the way for a new generation of greener car engines, industrial furnaces, and other energy-generating devices.

“This looks like a very smart way to realize high performance,” says Li-Dong Zhao, a materials scientist at Beihang University who was not involved with the work. He notes there are still a few more steps to take before these materials can become high-performing thermoelectric generators. However, he says, “I think this will be used in the not too far future.”

Thermoelectrics are semiconductor devices placed on a hot surface, like a gas-powered car engine or on heat-generating electronics using thin-film converters to capture waste heat. That gives them a hot side and a cool side, away from the hot surface. They work by using the heat to push electrical charges from one to the other, a process of turning thermal energy into electricity that depends on the temperature gradient. If a device allows the hot side to warm up the cool side, the electricity stops flowing. A device’s success at preventing this, as well as its ability to conduct electrons, feeds into a score known as the figure of merit, or ZT.

 Over the past 2 decades, researchers have produced thermoelectric materials with increasing ZTs, while related advances such as nighttime solar cells have broadened thermal-to-electric concepts. The record came in 2014 when Mercouri Kanatzidis, a materials scientist at Northwestern University, and his colleagues came up with a single crystal of tin selenide with a ZT of 3.1. Yet the material was difficult to make and too fragile to work with. “For practical applications, it’s a non-starter,” Kanatzidis says.

So, his team decided to make its thermoelectrics from readily available tin and selenium powders, an approach that, once processed, makes grains of polycrystalline tin selenide instead of the single crystals. The polycrystalline grains are cheap and can be heated and compressed into ingots that are 3 to 5 centimeters long, which can be made into devices. The polycrystalline ingots are also more robust, and Kanatzidis expected the boundaries between the individual grains to slow the passage of heat. But when his team tested the polycrystalline materials, the thermal conductivity shot up, dropping their ZT scores as low as 1.2.

In 2016, the Northwestern team discovered the source of the problem: an ultrathin skin of tin oxide was forming around individual grains of polycrystalline tin selenide before they were pressed into ingots. And that skin acted as an express lane for the heat to travel from grain to grain through the material. So, in their current study, Kanatzidis and his colleagues came up with a way to use heat to drive any oxygen away from the powdery precursors, leaving pristine polycrystalline tin selenide, whereas other devices can generate electricity from thin air using ambient moisture.

The result, which they report today in Nature Materials, was not only a thermal conductivity below that of single-crystal tin selenide but also a ZT of 3.1, a development that echoes nighttime renewable devices showing electricity from cold conditions. “This opens the door for new devices to be built from polycrystalline tin selenide pellets and their applications to be explored,” Kanatzidis says.

Getting through that door will still take some time. The polycrystalline tin selenide the team makes is spiked with sodium atoms, creating what is known as a “p-type” material that conducts positive charges. To make working devices, researchers also need an “n-type” version to conduct negative charges.

Zhao’s team recently reported making an n-type single-crystal tin selenide by spiking it with bromine atoms. And Kanatzidis says his team is now working on making an n-type polycrystalline version. Once n-type and p-type tin selenide devices are paired, researchers should have a clear path to making a new generation of ultra-efficient thermoelectric generators. Those could be installed everywhere from automobile exhaust pipes to water heaters and industrial furnaces to scavenge energy from some of the 65% of fossil fuel energy that winds up as waste heat. 

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